Vascular endothelial growth factor A is associated with the subsequent development of moderate or severe cardiac allograft vasculopathy in pediatric heart transplant recipients

Pediatric heart transplantation: Looking forward after five decades of learning

Heart transplantation has become the standard of care for pediatric patients with end-stage heart disease throughout the world. Since the first transplant was performed in 1967, the number of transplants has grown dramatically with 13 449 pediatric heart transplants being reported to The International Society of Heart and Lung Transplant (ISHLT) between January 1992 and June 30, 2018. Outcomes have consistently improved over the last few decades, specifically short-term outcomes. Most recent survival data demonstrate that recipients who survive to 1-year post-transplant have excellent long-term survival with more than 60% of those who were transplanted as infants being alive 25 years later. Nonetheless, the rates of graft loss beyond the first year have remained relatively constant over time; driven primarily by our poor understanding and lack of treatments for chronic allograft vasculopathy (CAV). Acute rejection, CAV, graft failure, and infection continue to be the major causes of death within the first 5 years post-transplant. In addition, renal dysfunction, malignancy, and the need for re-transplantation remain as significant issues that require close follow-up. Looking forward, key challenges include improving donor utilization rates (including donation after cardiac death (DCD) and the use of ex vivo perfusion devices), the development of non-invasive biomarkers for rejection, efforts to mitigate the long-term effects of immunosuppression, and prevention of CAV. It is not possible to cover the entire evolution of pediatric heart transplantation over the last five decades, but in this review, we hope to touch on key observations, lessons learned, and practice changes that have advanced the field, as well as glance ahead to the next decade.

Role of genetics in the development of cardiac allograft vasculopathy

BACKGROUND

The association between genetic polymorphisms and early cardiac allograft vasculopathy (CAV) development is relatively unexplored. Identification of genes involved in the CAV process may offer new insights into pathophysiology and lead to a wider range of therapeutic options.

METHODS

This prospective study of 109 patients investigated 44 single nucleotide polymorphisms (SNPs) within the susceptibility loci potentially related to coronary artery disease, carotid artery intima-media thickness (cIMT), and in nitric oxide synthase gene. Genotyping was done by the Fluidigm SNP Type assays and Fluidigm 48.48 Dynamic Array IFC. The intima thickness progression (IT) was evaluated by coronary optical coherence tomography performed 1 month and 12 months after heart transplantation (HTx).

RESULTS

During the first post-HTx year, the mean intima thickness (IT) increased by 24.0 ± 34.2 µm (p < 0.001) and lumen area decreased by ‒0.9 ± 1.8 mm2 (p < 0.001). The rs1570360 (A/G) SNP of the vascular endothelial growth factor A (VEGFA) gene showed the strongest association with intima thickness progression, even in the presence of the traditional CAV risk factors. SNPs previously related to carotid artery intima-media thickness rs11785239 (PRAG1), rs6584389 (PAX2), rs13225723 (LINC02577) and rs17477177 (CCDC71L), were among the five most significantly associated with IT progression but lost their significance once traditional CAV risk factors had been added.

CONCLUSION

Results of this study suggest that genetic variability may play an important role in CAV development. The vascular endothelial growth factor A gene SNP rs1570360 showed the strongest association with intima thickness (IT) progression measured by OCT, even in the presence of the traditional CAV risk factors (Tab. 3, Fig. 3, Ref. 36). Text in PDF www.elis.sk Keywords: cardiac allograft vasculopathy, optical coherence tomography, vascular endothelial growth factor A, intimal thickening, genetic polymorphism.

DDAH1 Promotes Lung Endothelial Barrier Repair by Decreasing Leukocyte Transendothelial Migration and Oxidative Stress in Explosion-Induced Lung Injury

Explosion-induced injury is the most commonly encountered wound in modern warfare and incidents. The vascular inflammatory response and subsequent oxidative stress are considered the key causes of morbidity and mortality among those in blast lung injury. It has been reported dimethylarginine dimethylaminohydrolase 1 (DDAH1) plays important roles in regulating vascular endothelial injury repair and angiogenesis, but its role in explosion-induced injury remains to be explained. To explore the mechanism of vascular injury in blast lung, 40 C57BL/6 wild type mice and 40 DDAH1 knockout mice were randomly equally divided into control group and blast group, respectively. Body weight, lung weight, and dry weight of the lungs were recorded. Diffuse vascular leakage was detected by Evans blue test. The serum inflammatory factors, nitric oxide (NO) contents, and ADMA level were determined through ELISA. Hematoxylin-eosin staining and ROS detection were performed for histopathological changes. Western blot was used to detect the proteins related to oxidative stress, cell adhesion molecules and leukocyte transendothelial migration, vascular injury, endothelial barrier dysfunction, and the DDAH1/ADMA/eNOS signaling pathway. We found that DDAH1 deficiency aggravated explosion-induced body weight reduction, lung weight promotion, diffuse vascular leakage histopathological changes, and the increased levels of inflammatory-related factors. Additionally, DDAH1 deficiency also increased ROS generation, MDA, and IRE-1α expression. Regarding vascular endothelial barrier dysfunction, DDAH1 deficiency increased the expression of ICAM-1, Itgal, Rac2, VEGF, MMP9, vimentin, and N-cadherin, while lowering the expression of occludin, CD31, and dystrophin. DDAH1 deficiency also exacerbated explosion-induced increase of ADMA and decrease of eNOS activity and NO contents. Our results indicated that explosion could induce severe lung injury and pulmonary vascular insufficiency, whereas DDAH1 could promote lung endothelial barrier repair and reduce inflammation and oxidative stress by inhibiting ADMA signaling which in turn increased eNOS activity.

Cardiac allograft vasculopathy: A review

BACKGROUND

Heart transplantation has become the standard of care for pediatric patients with end-stage heart disease, and outcomes have consistently improved over the last few decades. CAV, however, remains a leading cause of morbidity and mortality in heart transplantation and is the leading cause of death beyond 3 years post-transplantation. We sought out to provide an in-depth overview of CAV in the pediatric heart transplant population.

METHODS

Database searches were conducted in both Medline and Embase on the topic of cardiac vasculopathy in pediatric heart transplant recipients. The search used five broad concept terms: heart transplant; pediatric; CAV; diagnosis, prognosis, and risk factors; and guidelines and reviews. References were captured if there was at least one term in each of the concepts. The search was limited to articles in the English language.

RESULTS

A total of 148 articles were identified via the literature search with further articles identified via review of references. Pediatric data regarding the etiology and development of CAV remain limited although knowledge about the immune and non-immune factors playing a role are increasing. CAV continues to be difficult to detect with many invasive and non-invasive methods available, yet their effectiveness in the detection of CAV remains suboptimal. There remains no proven medical intervention to treat or reverse established CAV disease, and CAV is associated with high rates of graft loss once detected. However, several medications are used in hopes of preventing, slowing progression, or modifying the outcomes.

CONCLUSION

This review provides a comprehensive overview of CAV, discusses its clinical presentation, risk factors, diagnostic tools used to identify CAV in the pediatric population, and highlights the current therapeutic options and the need for ongoing research.

The novel proteomic signature for cardiac allograft vasculopathy

AIMS

Cardiac allograft vasculopathy (CAV) is the major long-term complication after heart transplantation, leading to mortality and re-transplantation. As available non-invasive biomarkers are scarce for CAV screening, we aimed to identify a proteomic signature for CAV.

METHODS AND RESULTS

We measured urinary proteome by capillary electrophoresis coupled with mass spectrometry in 217 heart transplantation recipients (mean age: 55.0 ± 14.4 years; women: 23.5%), including 76 (35.0%) patients with CAV diagnosed by coronary angiography. We randomly and evenly grouped participants into the derivation cohort (n = 108, mean age: 56.4 ± 13.8 years; women: 22.2%; CAV: n = 38) and the validation cohort (n = 109, mean age: 56.4 ± 13.8 years; women: 24.8%, CAV: n = 38), stratified by CAV. Using the decision tree-based machine learning methods (extreme gradient boost), we constructed a proteomic signature for CAV discrimination in the derivation cohort and verified its performance in the validation cohort. The proteomic signature that consisted of 27 peptides yielded areas under the curve of 0.83 [95% confidence interval (CI): 0.75-0.91, P < 0.001] and 0.71 (95% CI: 0.60-0.81, P = 0.001) for CAV discrimination in the derivation and validation cohort, respectively. With the optimized threshold of 0.484, the sensitivity, specificity, and accuracy for CAV differentiation in the validation cohort were 68.4%, 73.2%, and 71.6%, respectively. With adjustment of potential clinical confounders, the signature was significantly associated with CAV [adjusted odds ratio: 1.31 (95% CI: 1.07-1.64) for per 0.1% increment in the predicted probability, P = 0.012]. Diagnostic accuracy significantly improved by adding the signature to the logistic model that already included multiple clinical risk factors, suggested by the integrated discrimination improvement of 9.1% (95% CI: 2.5-15.3, P = 0.005) and net reclassification improvement of 83.3% (95% CI: 46.7-119.5, P < 0.001). Of the 27 peptides, the majority were the fragments of collagen I (44.4%), collagen III (18.5%), collagen II (3.7%), collagen XI (3.7%), mucin-1 (3.7%), xylosyltransferase 1 (3.7%), and protocadherin-12 (3.7%). Pathway analysis performed in Reactome Pathway Database revealed that the multiple pathways involved by the signature were related to the pathogenesis of CAV, such as collagen turnover, platelet aggregation and coagulation, cell adhesion, and motility.

CONCLUSIONS

This pilot study identified and validated a urinary proteomic signature that provided a potential approach for the surveillance of CAV. These proteins might provide insights into CAV pathological processes and call for further investigation into personalized treatment targets.

Effects of mTOR inhibitor-related proteinuria on progression of cardiac allograft vasculopathy and outcomes among heart transplant recipients

We have previously described the use of sirolimus (SRL) as primary immunosuppression following heart transplantation (HT). The advantages of this approach include attenuation of cardiac allograft vasculopathy (CAV), improvement in glomerular filtration rate (GFR), and reduced malignancy. However, in some patients SRL may cause significant proteinuria. We sought to investigate the prognostic value of proteinuria after conversion to SRL. CAV progression and adverse clinical events were studied. CAV progression was assessed by measuring the Δ change in plaque volume (PV) and plaque index (PI) per year using coronary intravascular ultrasound. Proteinuria was defined as Δ urine protein ≥300 mg/24 h at 1 year after conversion to SRL. Overall, 137 patients were analyzed (26% with proteinuria). Patients with proteinuria had significantly lower GFR (P = .005) but similar GFR during follow-up. Delta PV (P < .001) and Δ PI (P = .001) were significantly higher among patients with proteinuria after adjustment for baseline characteristics. Multivariate Cox regression analysis showed higher all-cause mortality (hazard ratio 3.8; P = .01) with proteinuria but similar risk of CAV-related events (P = .61). Our results indicate that proteinuria is a marker of baseline renal dysfunction, and that HT recipients who develop proteinuria after conversion to SRL have less attenuation of CAV progression and higher mortality risk.

Angiogenesis Inhibitors as Anti-Cancer Therapy Following Renal Transplantation: A Case Report and Review of the Literature

Solid organ transplant recipients on long-term immunosuppressive medication are at increased risk of developing malignancy, and treatment of advanced cancers with angiogenesis inhibitors in this context has not been widely studied. We present a case of recurrent high-grade serous ovarian carcinoma treated with paclitaxel and bevacizumab in the context of prior renal transplantation where the patient responded well to treatment with controlled toxicities, discussing the potential for increased rates of adverse events and drug interactions in this select population.

Granzymes in cardiovascular injury and disease

Chronic inflammation and impaired wound healing play important roles in the pathophysiology of cardiovascular diseases. Moreover, the aberrant secretion of proteases plays a critical role in pathological tissue remodeling in chronic inflammatory conditions. Human Granzymes (Granule secreted enzymes - Gzms) comprise a family of five (GzmA, B, H, K, M) cell-secreted serine proteases. Although each unique in function and substrate specificities, Gzms were originally thought to share redundant, intracellular roles in cytotoxic lymphocyte-induced cell death. However, an abundance of evidence has challenged this dogma. It is now recognized, that individual Gzms exhibit unique substrate repertoires and functions both intracellularly and extracellularly. In the extracellular milieu, Gzms contribute to inflammation, vascular dysfunction and permeability, reduced cell adhesion, release of matrix-sequestered growth factors, receptor activation, and extracellular matrix cleavage. Despite these recent findings, the non-cytotoxic functions of Gzms in the context of cardiovascular disease pathogenesis remain poorly understood. Minimally detected in tissues and bodily fluids of normal individuals, GzmB is elevated in patients with acute coronary syndromes, coronary artery disease, and myocardial infarction. Pre-clinical animal models have exemplified the importance of GzmB in atherosclerosis, aortic aneurysm, and cardiac fibrosis as animals deficient in GzmB exhibit reduced tissue remodeling, improved disease phenotypes and increased survival. Although a role for GzmB in cardiovascular disease is described, further work to elucidate the mechanisms that underpin the remaining human Gzms activity in cardiovascular disease is necessary. The present review provides a summary of the pre-clinical and clinical evidence, as well as emerging areas of research pertaining to Gzms in tissue remodeling and cardiovascular disease.

Surveillance for cardiac allograft vasculopathy: Practice variations among 50 pediatric heart transplant centers

BACKGROUND

Coronary allograft vasculopathy (CAV) is a leading cause of mortality after heart transplantation (HT) in children. Variation in CAV screening practices may impact detection rates and patient outcomes.

METHODS

Among 50 Pediatric Heart Transplant Society (PHTS) sites from 2001 to 2016, coronary evaluations were classified as angiography or non-invasive testing, and angiograms were designated as routine or symptom based. CAV detection rates stratified by routine vs symptom-based angiograms were calculated. Freedom from CAV and mortality after CAV diagnosis, stratified by study indication, were calculated.

RESULTS

A total of 3,442 children had 13,768 coronary evaluations; of these, 97% (n = 13,012) were for routine surveillance, and only 3% (n = 333) were for cause. Over the study period, CAV was detected in 472 patients (14%). Whereas 58% (n = 29) of PHTS sites evaluate by angiography alone, 42% reported supplementing with a non-invasive test, although only 423 non-invasive studies were reported. Angiographic detection of CAV was higher for symptom-based testing than for routine testing (29% vs 4%, p < 0.0001), although routine testing identified a majority of cases (88%; n = 414). The 10-year freedom from CAV was 77% overall. Once CAV is detected, 5-year graft survival was 58%, with lower survival for patients diagnosed after symptoms angiogram than after routine angiogram (30% vs 62%; p < 0.0001).

CONCLUSIONS

Development of a robust model for CAV risk should allow low-risk patients to undergo less frequent invasive angiography without adverse impact on CAV detection rates or outcomes.

Early immune biomarkers and intermediate-term outcomes after heart transplantation: Results of Clinical Trials in Organ Transplantation-18

Clinical Trials in Organ Transplantation-18 (CTOT-18) is a follow-up analysis of the 200-subject multicenter heart transplant CTOT-05 cohort. CTOT-18 aimed to identify clinical, epidemiologic, and biologic markers associated with adverse clinical events past 1 year posttransplantation. We examined various candidate biomarkers including serum antibodies, angiogenic proteins, blood gene expression profiles, and T cell alloreactivity. The composite endpoint (CE) included death, retransplantation, coronary stent, myocardial infarction, and cardiac allograft vasculopathy. The mean follow-up was 4.5 ± SD 1.1 years. Subjects with serum anti-cardiac myosin (CM) antibody detected at transplantation and at 12 months had a higher risk of meeting the CE compared to those without anti-CM antibody (hazard ratio [HR] = 2.9, P = .046). Plasma VEGF-A and VEGF-C levels pretransplant were associated with CE (odds ratio [OR] = 13.24, P = .029; and OR = 0.13, P = .037, respectively). Early intravascular ultrasound findings or other candidate biomarkers were not associated with the study outcomes. In conclusion, anti-CM antibody and plasma levels of VEGF-A and VEGF-C were associated with an increased risk of adverse events. Although this multicenter report supports further evaluation of the mechanisms through which anti-CM antibody and plasma angiogenesis proteins lead to allograft injury, we could not identify additional markers of adverse events or potential novel therapeutic targets.

Elevated serum vascular endothelial growth factor and development of cardiac allograft vasculopathy in children

BACKGROUND

Cardiac allograft vasculopathy (CAV) is a leading cause of retransplantation and death in pediatric heart transplant recipients. Our aim was to evaluate the association between serum vascular endothelial growth factor-A (VEGF) and CAV development in the pediatric heart transplant population.

METHODS

In this retrospective study performed at a university hospital, VEGF concentrations were measured by enzyme-linked immunosorbent assay in banked serum from pediatric heart transplant recipients undergoing routine cardiac catheterization. In subjects with CAV (n = 29), samples were obtained at 2 time-points: before CAV diagnosis (pre-CAV) and at the time of initial CAV diagnosis (CAV). In subjects without CAV (no-CAV, n = 16), only 1 time-point was used. VEGF concentrations (n = 74) were assayed in duplicate.

RESULTS

Serum VEGF is elevated in pediatric heart transplant recipients before catheter-based diagnosis of CAV (no-CAV mean: 144.0 ± 89.05 pg/ml; pre-CAV mean: 316.2 ± 118.3 pg/ml; p = 0.0002). Receiver-operating characteristic curve analysis of pre-CAV VEGF levels demonstrated an area under the curve of 87.7% (p = 0.0002), with a VEGF level of 226.3 pg/ml predicting CAV development with 77.8% sensitivity and 91.7% specificity. VEGF is similarly elevated in subjects with angiographically diagnosed CAV and in those with normal angiography but intravascular ultrasound (IVUS) evidence of CAV.

CONCLUSIONS

The increase in serum VEGF before onset of detectable CAV is fundamental to its utility as a predictive biomarker and suggests further investigations of VEGF in the pathogenesis of CAV are warranted in the pediatric heart transplant population.

Cardiopulmonary, biomarkers, and vascular responses to acute hypoxia following cardiac transplantation

Previous studies have suggested good adaptation of cardiac transplant (CTx) recipients to exposure to a high altitude. No studies have investigated the cardiopulmonary and biomarker responses to acute hypoxic challenges following CTx. Thirty-six CTx recipients and 17 age-matched healthy controls (HC) were recruited. Sixteen (16) patients (42%) had cardiac allograft vasculopathy (CAV). Cardiopulmonary responses to maximal and submaximal exercise at 21% O₂ , 20-minutes hypoxia (11.5% O₂ ), and following a 10-minute exposure to 11.5% O₂ using 30% of peak power output were completed. Vascular endothelial growth factor (VEGF), interleukin-6 (IL-6), suppression of tumorigenicity 2 (ST2) were measured at baseline and at peak stress. Endothelial peripheral function was assessed using near-infrared spectroscopy. Compared with HC, CTx presented a lesser O₂ desaturation both at rest (-19.4 ± 6.8 [CTx] vs -24.2 ± 6.0% O₂ [HC], P < 0.05) and following exercise (-23.2 ± 4.9 [CTx] vs -26.2 ± 4.7% O₂ [HC], P < 0.05). CTx patients exhibited a significant decrease in peak oxygen uptake. IL-6 and VEGF levels were significantly higher in CTx recipients in basal conditions but did not change in response to acute stress. CTx patients exhibit a favorable ventilatory and overall response to hypoxic stress. These data provide further insights on the good adaptability of CTx to exposure to high altitude.

Angiogenesis on coronary angiography is a marker for accelerated cardiac allograft vasculopathy as assessed by intravascular ultrasound

BACKGROUND

Errant neovascularization and coronary artery fistulae (CAF) are frequently observed after cardiac transplantation. The relationship between angiographic neovascularization/CAF and coronary plaque progression is unknown.

METHODS

Angiography and intravascular ultrasound were routinely performed at 4-6 weeks and 1-year post-transplant. Pts were divided into three groups: no angiographic angiogenesis (Group 1), neovascularization only (Group 2), and CAF (Group 3). First-year changes in maximal intimal thickness (MIT), maximal intimal area (MIA), and percent atheroma volume (PAV) were compared between groups.

RESULTS

The 106 pts were included, 40/106 in Group 1, 42/106 in Group 2, and 24/106 in Group 3. Respectively, first-year ΔMIT was 0.14 ± 0.13 mm, 0.32 ± 0.26 mm, and 0.50 ± 0.34 mm, P < .001. ΔMIA was 0.6 ± 0.6 mm² , 1.7 ± 1.8 mm² , and 3.0 ± 2.6 mm² , P < .001. ΔPAV was 2.3 ± 2.5%, 6.0 ± 5.1%, and 9.6 ± 9.0%, P < .001. Rapid plaque progression occurred in 1/40 (2.5%) pts in Group 1, 12/42 (28.6%) in Group 2, and 12/24 (50%) in Group 3, P < .001. Multivariate analysis identified both antithymocyte globulin and presence of CAF as independently associated with rapid plaque progression: OR 0.29 (P = .038) and 4.04 (P = .014).

CONCLUSION

Neovascularization and CAF are commonly present on surveillance angiography after cardiac transplantation and may signify amplified angiogenesis. Their presence is associated with accelerated coronary plaque progression by IVUS.

The intragraft microenvironment as a central determinant of chronic rejection or local immunoregulation/tolerance

PURPOSE OF REVIEW

Chronic rejection is associated with persistent mononuclear cell recruitment, endothelial activation and proliferation, local tissue hypoxia and related biology that enhance effector immune responses. In contrast, the tumor microenvironment elicits signals/factors that inhibit effector T cell responses and rather promote immunoregulation locally within the tissue itself. The identification of immunoregulatory check points and/or secreted factors that are deficient within allografts is of great importance in the understanding and prevention of chronic rejection.

RECENT FINDINGS

The relative deficiency of immunomodulatory molecules (cell surface and secreted) on microvascular endothelial cells within the intragraft microenvironment, is of functional importance in shaping the phenotype of rejection. These regulatory molecules include coinhibitory and/or intracellular regulatory signals/factors that enhance local activation of T regulatory cells. For example, semaphorins may interact with endothelial cells and CD4 T cells to promote local tolerance. Additionally, metabolites and electrolytes within the allograft microenvironment may regulate local effector and regulatory cell responses.

SUMMARY

Multiple factors within allografts shape the microenvironment either towards local immunoregulation or proinflammation. Promoting the expression of intragraft cell surface or secreted molecules that support immunoregulation will be critical for long-term graft survival and/or alloimmune tolerance.