Histopathology of aortic complications in bicuspid aortic valve versus Marfan syndrome: relevance for therapy?

The role of transforming growth factor beta in bicuspid aortic valve aortopathy

A bicuspid aortic valve (BAV) is the most prevalent congenital cardiac deformity, which is associated with an increased risk to develop a thoracic aortic aneurysm and/or an aortic dissection as compared to persons with a tricuspid aortic valve. Due to the high prevalence of a BAV in the general population and the associated life-long increased risk for adverse vascular events, BAV disease places a considerable burden on the public health. The aim of the present review is to discuss the role of transforming growth factor beta (TGF-β) signaling in the development of the vascular wall and on how this complex signaling pathway may be involved in thoracic aortic aneurysm formation in tricuspid and BAV patients.

Coronary artery dilation associated with bicuspid and unicuspid aortic valve disease in children: a series of 17 patients

INTRODUCTION

Coronary artery dilation associated with bicuspid/unicuspid aortic valves is described in adults with limited data in children. We aimed to describe the clinical course of children with bicuspid/unicuspid aortic valves and coronary dilation including coronary Z-score changes over time, association of coronary changes with aortic valve anatomy/function, and complications.

MATERIALS AND METHODS

Institutional databases were searched for children ≤18 years with both bicuspid/unicuspid aortic valves and coronary dilation (1/2006-6/2021). Kawasaki disease and isolated supra-/subvalvar aortic stenosis were excluded. Statistics were descriptive with associations measured by Fisher's exact test and overlapping 83.7% confidence intervals.

RESULTS

Of 17 children, bicuspid/unicuspid aortic valve was diagnosed at birth in 14 (82%). Median age at coronary dilation diagnosis was 6.4 years (range: 0-17.0). Aortic stenosis was present in 14 (82%) [2 (14%) moderate, 8 (57%) severe]; 10 (59%) had aortic regurgitation; 8 (47%) had aortic dilation. The right coronary was dilated in 15 (88%), left main in 6 (35%), and left anterior descending in 1 (6%) with no relationship between leaflet fusion pattern or severity of aortic regurgitation/stenosis on coronary Z-score. Follow-up evaluations were available for 11 (mean 9.3 years, range 1.1-14.8) with coronary Z-scores increasing in 9/11 (82%). Aspirin was used in 10 (59%). There were no deaths or coronary artery thrombosis.

DISCUSSION

In children with bicuspid/unicuspid aortic valves and coronary dilation, the right coronary artery was most frequently involved. Coronary dilation was observed in early childhood and frequently progressed. Antiplatelet medication use was inconsistent, but no child died nor developed thrombosis.

The Importance of Aortic Valve Bicuspid Phenotype in Valvular Evolution in Pediatric Patients: A Case Report and Literature Mini-Review

Bicuspid aortic valve (BAV) is the most commonly encountered congenital malformation in the pediatric population, associated with aortic leaflet degeneration and aortopathy. However, studies on BAV and its complications in children are limited. We present the case of a 16-year-old with type 1B BAV with a raphe with fusion between the right and non-coronary cusps who exhibited severe aortic stenosis, regurgitation, and progressive dilatation of the ascending aorta. Surgical intervention, including aortic valve and aortic root replacement, was performed due to the patient's deteriorating condition. Histopathological examination revealed degenerative changes and calcifications in the aortic valve and mucoid fibrosis in the ascending aorta. The results are consistent with BAV patients being predisposed to aortic stenosis and regurgitation due to increased mechanical stress and hemodynamic abnormalities. Although more common in adults and a rare complication in pediatric patients, calcification was previously observed concurrently with rapid valve degeneration in our daily practice. Further studies are needed to improve our understanding of the mechanisms underlying BAV-related complications and refine treatment strategies for pediatric patients.

Intrinsic histological and morphological abnormalities of the pediatric thoracic aorta in bicuspid aortic valve patients are predictive for future aortopathy

BACKGROUND

Patients with a bicuspid aortic valve (BAV) have an increased risk to develop aortic complications. Many studies are pointing towards a possible embryonic explanation for the development of both a bicuspid aortic valve as well as a defective ascending aortic wall in these patients. The fetal and newborn ascending aortic wall has however scarcely been studied in bicuspid aortic valve patients. We hypothesize that early histopathological defects might already be visible in the fetal and pediatric ascending aortic wall of bicuspid aortic valve patients, indicating at an early embryonic defect.

METHODS

Non-dilated BAV ascending aortic wall samples were collected (n = 40), categorized in five age groups: premature (age range 17.5 weeks + days GA till 37.6 weeks + days GA) 2. neonate (age range 1 - 21 days) 3. infant (age range 1 month - 4 years) 4. adolescent (age range 12 years - 15 years) and 5. adult (age range 41 - 72 years). Specimen were studied for intimal and medial histopathological features.

RESULTS

The premature ascending aortic wall has a significantly thicker intimal and significantly thinner medial layer as compared to all other age categories (p < 0.05). After birth the intimal thickness decreases significantly. The medial layer increases in thickness before adulthood (p < 0.05) with an increasing number of elastic lamellae (p < 0.01) and interlamellar mucoid extracellular matrix accumulation (p < 0.0001). Intimal atherosclerosis was scarce and medial histopathological features such as overall medial degeneration, smooth muscle cell nuclei loss and elastic fiber fragmentation were not appreciated in the BAV ascending aortic wall of any age.

CONCLUSIONS

The main characteristics of a bicuspid ascending aortic wall are already present before adulthood, albeit not before birth. Considering the early manifestations of ascending aortic wall pathology in bicuspid aortic valve patients, the pediatric population should be considered while searching for markers predictive for future aortopathy.

Adventitial adaptive immune cells are associated with ascending aortic dilatation in patients with a bicuspid aortic valve

Background

Bicuspid aortic valve (BAV) is associated with ascending aorta aneurysms and dissections. Presently, genetic factors and pathological flow patterns are considered responsible for aneurysm formation in BAV while the exact role of inflammatory processes remains unknown.

Methods

In order to objectify inflammation, we employ a highly sensitive, quantitative immunohistochemistry approach. Whole slides of dissected, dilated and non-dilated ascending aortas from BAV patients were quantitatively analyzed.

Results

Dilated aortas show a 4-fold increase of lymphocytes and a 25-fold increase in B lymphocytes in the adventitia compared to non-dilated aortas. Tertiary lymphoid structures with B cell follicles and helper T cell expansion were identified in dilated and dissected aortas. Dilated aortas were associated with an increase in M1-like macrophages in the aorta media, in contrast the number of M2-like macrophages did not change significantly.

Conclusion

This study finds unexpected large numbers of immune cells in dilating aortas of BAV patients. These findings raise the question whether immune cells in BAV aortopathy are innocent bystanders or contribute to the deterioration of the aortic wall.

Can transforming growth factor beta and downstream signalers distinguish bicuspid aortic valve patients susceptible for future aortic complications?

Patients with a bicuspid aortic valve have an extreme high risk to develop a thoracic aortic aneurysm and dissection (TAAD). TAADs form a leading cause of death worldwide, with the majority of deaths being preventable if individuals at risk are identified and properly managed. Risk stratification for TAADs in bicuspidy is so far solely based on the aortic diameter. Exclusive use of aortic wall dimension, as in the current guidelines, is however not sufficient in selecting patients vulnerable for future aortic wall complications. Moreover, there are no effective medical treatments for TAADs to retain progressive aortic dilatation and thus prevent or delay aortic complications. Only surgical replacement of the aorta increases life expectancy in patients with a risk for a TAAD. Therefore, the next major challenge in the management of TAADs is the development of a personalized patient-tailored risk stratification for early detection of patients with an increased risk for TAADs, who will benefit from surgical resection of the aorta. Several signaling pathways have been studied in recent times to develop a patient specific risk stratification model. In this paper we discuss TGF-β signaling and downstream signalers as potential markers for future aortic complications in bicuspid aortic valve patients.

Risk for acquired coronary artery disease in genetic vs. congenital thoracic aortopathy

Objective

Patients with Marfan syndrome (MFS) and patients with a bicuspid aortic valve (BAV) have a significantly increased risk to develop thoracic aortopathy. Both conditions share many pathophysiological mechanisms leading to aortic complications. Bicuspidy is known to have a low risk for acquired coronary artery sclerosis. The aim of this study is to determine the risk of coronary sclerosis in MFS patients.

Methods

Marfan syndrome patients with an aortic root dilatation, which were surgically treated between 1999 and 2017, were included and matched with BAV and tricuspid aortic valves (TAV) patients based on sex and age. Cardiovascular risk profiles were determined in all three groups. Coronary sclerosis was graded in all patients on coronary imaging (coronary angiography or computed tomography) using a coronary artery scoring method, which divides the coronaries in 28 segments and scores non-obstructive (20-49% sclerosis) and obstructive coronary sclerosis (>49% sclerosis) in each segment.

Results

A total of 90 matched patients (30 within each group) were included. MFS patients showed less cardiovascular risk factors compared to BAV and TAV patients. TAV patients had higher amounts of obstructive coronary sclerosis as compared to BAV patients (p = 0.039) and MFS patients (p = 0.032). No difference in non- and obstructive coronary artery disease (CAD) was found between the MFS and BAV population.

Conclusion

Marfan syndrome and bicuspid aortic valve patients have a significantly lower risk for, and prevalence of CAD as compared to TAV individuals.

Monocyte-to-HDL-cholesterol ratio is associated with Ascending Aorta Dilatation in Patients with Bicuspid Aortic Valve

BACKGROUND

The importance of monocyte count-to-HDL-cholesterol ratio (MHR) in cardio- vascular diseases has been shown in various studies. Ascending aortic dilatation (AAD) is a common complication in the patients with bicuspid aortic valve. In this study, we aimed to investigate the relationship between MHR and the presence of aortic dilatation in the patients with bicuspid aortic valve.

METHODS

The study population included totally 347 patients with bicuspid aortic valve.169 patients with aortic dilatation (ascending aorta diameter ≥ 4.0 cm) and 178 patients with no aortic dilatation. Echocardiographic and laboratory measurement was done and compared between groups.

RESULTS

The mean age of the participants was 44.7 ± 15.4 years and average ascending aorta diameter was 3.2 ± 0.3 cm in dilatation negative group and 4.4 ± 0.4 cm in positive group. MHR was significantly increased in in patients with aortic dilatation. MHR and uric acid level was independently associated with the presence of aortic dilatation in the patients with bicuspid aortic valve.

CONCLUSION

We found a significant relationship between MHR and aortic dilatation in the patients with bicuspid aortic valve.

A Systematic Histopathologic Evaluation of Type-A Aortic Dissections Implies a Uniform Multiple-Hit Causation

(1) Background: The pathophysiologic basis of an acute type A aortic dissection (TAAD) is largely unknown. In an effort to evaluate vessel wall defects, we systematically studied aortic specimens in TAAD patients. (2) Methods: Ascending aortic wall specimens (n = 58, mean age 63 years) with TAAD were collected. Autopsy tissues (n = 17, mean age 63 years) served as controls. All sections were studied histopathologically. (3) Results: Pathomorphology in TAAD showed predominantly moderate elastic fiber fragmentation/loss, elastic fiber thinning, elastic fiber degeneration, mucoid extracellular matrix accumulation, smooth muscle cell nuclei loss, and overall medial degeneration. The control group showed significantly fewer signs of those histopathological features (none-mild, p = 0.00). It was concluded that the dissection plane consistently coincides with the vasa vasorum network, and that TAAD associates with a significantly thinner intimal layer p = 0.005). (4) Conclusions: On the basis of the systematic evaluation and the consistent presence of diffuse, pre-existing medial defects, we hypothesize that TAAD relates to a developmental defect of the ascending aorta and is caused by a triple-hit mechanism that involves (I) an intimal tear; and (II) a diseased media, which allows (III) propagation of the tear towards the plane of the vasa vasorum where the dissection further progresses.

Aortic Regurgitation Is Associated With Ascending Aortic Remodeling in the Nondilated Aorta

OBJECTIVE

The probability of aortic complications in patients with bicuspid aortic valve is higher in association with aortic regurgitation (AR) compared with aortic stenosis (AS) or normally functioning valves. The objective of this study was to determine whether this is related to the specific characteristics of aneurysmatic dilatation that includes AR or whether AR itself has a negative impact on the aortic wall, independent of aneurysmatic dilatation. Approach and Results: Nondilated aortic specimens were harvested intraoperatively from individuals with tricuspid aortic valves and either AS (n=10) or AR (n=16). For controls, nondilated aortas were harvested during autopsies from individuals with tricuspid aortic valves and no evidence of aortic valve disease (n=10). Histological and immunohistochemical analyses revealed that compared with control aortas, overall medial degeneration was more severe in AR-aortas (P=0.005) but not AS-aortas (P=0.23). This pathological remodeling included mucoid extracellular matrix accumulation (P=0.005), elastin loss (P=0.003), elastin fragmentation (P=0.008), and decreased expression of fibrillin (P=0.003) and collagen (P=0.008). Furthermore, eNOS (endothelial nitric oxide synthase) expression was decreased in the intima (P=0.0008) and in vasa vasorum (P=0.004) of AR-aortas but not AS-aortas (all P>0.05). Likewise, subendothelial apoptosis was increased in AR-aortas (P=0.03) but not AS-aortas (P=0.50).

CONCLUSIONS

AR has a negative effect on the nondilated ascending aortic wall. Accordingly, our results support the need for more detailed studies of the aortic wall in relation to aortic valve disease and may ultimately lead to more aggressive clinical monitoring and/or surgical criteria for patients with relevant AR. Graphic Abstract: A graphic abstract is available for this article.

Retinal and Choroidal Vasculature in Patients with Marfan Syndrome

Purpose

To assess the retinal and choroidal vasculature in patients with genetically confirmed Marfan syndrome (MfS).

Methods

This prospective, case-control, observational study included 48 eyes of 24 patients with a genetic diagnosis of MfS and compared them with 52 eyes of 26 healthy controls. Best-corrected visual acuity, choroidal and retinal thickness measured by spectral domain-optical coherence tomography, retinal and choroidal vasculature characterized by optical coherence tomography angiography, were collected. A genetic counseling was carried out. A transthoracic echocardiogram was performed to evaluate the dimension of the aortic root, the ascending aorta and the left ventricle function and dimensions.

Results

A significant decrease in the superficial and deep retinal capillary plexi vessel density (VD) was evident, such as a decrease in the choriocapillaris plexus VD. In patients with MfS, a negative correlation between left ventricular diameter and the VD of the superficial and deep plexi was observed. Patients with MfS with greater posterior wall and interventricular septum dimensions had lower VD in both plexi (P < 0.05). Moreover, there was a negative correlation between the dimension of the ascending aorta and foveal choriocapillary VD. In patients with MfS, increasing diameter of the ascending aorta was associated with a lower foveal choriocapillary VD (P < 0.05).

Conclusions

The severity of MfS correlates with the impairment of the retinal and choroidal vasculature.

Translational Relevance

Optical coherence tomography angiography may be a reproducible and noninvasive tool to study retinal blood flow in patients with MfS, with potential diagnostic and prognostic value.

Marfan Syndrome Versus Bicuspid Aortic Valve Disease: Comparative Analysis of Obstetric Outcome and Pregnancy-Associated Immediate and Long-Term Aortic Complications

Pregnancy poses a threat to women with aortopathy. Conclusive data on the obstetric and aortic outcome in this risk collective, especially when it comes to aortic complications in the long term, are still missing. This study offers a comparative analysis of pregnancy-associated outcome in 113 consecutive women with Marfan syndrome or bicuspid aortic valve disease, including 46 ever-pregnant and 37 never-pregnant women with Marfan syndrome, and 23 ever-pregnant and 7 never-pregnant females with bicuspid aortic valve disease. The overall obstetric outcome was comparable between ever-pregnant women with Marfan syndrome and with bicuspid aortic valve disease (p = 0.112). Pregnancy-associated aortic dissection occurred in two women with Marfan syndrome (3%) during a total of 62 completed pregnancies, whereas no single case of aortic event occurred in women with bicuspid aortic valve disease during a total of 36 completed pregnancies (p = 0.530). In the long-term follow-up, aortic dissection occurred in 21% of ever-pregnant women with Marfan syndrome, but in none of the women with bicuspid aortic valve disease (p = 0.022). Proximal aortic surgery was performed with similar frequency in ever-pregnant women with Marfan syndrome and with bicuspid aortic valve disease in the long term (p = 0.252). However, ever-pregnant women with Marfan syndrome were younger when surgery was performed (44 ± 9 vs. 59 ± 7 years; p = 0.041). In Marfan syndrome, long-term growth of the aorta was comparable between ever-pregnant and never-pregnant women. Pregnancy thus exhibited an increased immediate aortic risk only in women with Marfan syndrome, but not in women with bicuspid aortic valve disease. Previous pregnancy did not relate to an increased long-term risk of adverse aortic events in women with Marfan syndrome or with bicuspid aortic valve disease.

The Development of the Ascending Aortic Wall in Tricuspid and Bicuspid Aortic Valve: A Process from Maturation to Degeneration

Background: Patients with a bicuspid aortic valve (BAV) have an increased risk for aortic dilation and dissection. In this study, we provide a histological stratification of the developing aorta in the tricuspid aortic valve (TAV) and the BAV populations as a reference for future studies on aortopathy and related syndromes. Methods: Non-dilated TAV and BAV ascending aortic wall samples were collected, including 60 TAV (embryonic–70 years) and 32 BAV specimens (fetal–72 years, categorized in eight age groups. Results: In TAV, intimal development starts in the neonatal phase. After birth, the thickness of the medial layer increases significantly by increase of elastic lamellae up to and including the “young child” phase stabilizing afterwards. The BAV shows already prenatal intimal thickening becoming significantly thinner after birth subsequently stabilizing. In BAV, increase in elastic lamellae is seen between the young child and the adolescent phases, stabilizing afterwards. Conclusions: Vascular development in TAV is described in three phases: maturation, stabilization, and degeneration. For BAV, the development can be described in two phases: maturation (already prenatally) and degeneration. After birth, the development of the aorta is characterized by degeneration, leading to weakening of the ascending aortic wall and increasing the risk of aortopathy.

Endothelial/Epithelial Mesenchymal Transition in Ascending Aortas of Patients With Bicuspid Aortic Valve

Thoracic aortic aneurysm (TAA) is the progressive enlargement of the aorta due to destructive changes in the connective tissue of the aortic wall. Aneurysm development is silent and often first manifested by the drastic events of aortic dissection or rupture. As yet, therapeutic agents that halt or reverse the process of aortic wall deterioration are absent, and the only available therapeutic recommendation is elective prophylactic surgical intervention. Being born with a bicuspid instead of the normal tricuspid aortic valve (TAV) is a major risk factor for developing aneurysm in the ascending aorta later in life. Although the pathophysiology of the increased aneurysm susceptibility is not known, recent studies are suggestive of a transformation of aortic endothelium into a more mesenchymal state i.e., an endothelial-to-mesenchymal transition in these individuals. This process involves the loss of endothelial cell features, resulting in junction instability and enhanced vascular permeability of the ascending aorta that may lay the ground for increased aneurysm susceptibility. This finding differentiates and further emphasizes the specific characteristics of aneurysm development in individuals with a bicuspid aortic valve (BAV). This review discusses the possibility of a developmental fate shared between the aortic endothelium and aortic valves. It further speculates about the impact of aortic endothelium phenotypic shift on aneurysm development in individuals with a BAV and revisits previous studies in the light of the new findings.

The American Association for Thoracic Surgery consensus guidelines on bicuspid aortic valve-related aortopathy: Full online-only version

Bicuspid aortic valve disease is the most common congenital cardiac disorder, being present in 1% to 2% of the general population. Associated aortopathy is a common finding in patients with bicuspid aortic valve disease, with thoracic aortic dilation noted in approximately 40% of patients in referral centers. Several previous consensus statements and guidelines have addressed the management of bicuspid aortic valve-associated aortopathy, but none focused entirely on this disease process. The current guidelines cover all major aspects of bicuspid aortic valve aortopathy, including natural history, phenotypic expression, histology and molecular pathomechanisms, imaging, indications for surgery, surveillance, and follow-up, and recommendations for future research. It is intended to provide clinicians with a current and comprehensive review of bicuspid aortic valve aortopathy and to guide the daily management of these complex patients.

Aortic root surgery in Marfan syndrome

Marfan syndrome (MFS) is an autosomal dominant connective disease etiologically related with FBN-1 gene mutation. The altered microfibril protein structure result in characteristic cardiovascular abnormalities including aortic root dilatation, aortic root aneurysms, and aortic dissections. Aortic root aneurysms and subsequent dissection are the major causes of reduced life expectancy in MFS patients. Prophylactic aortic root replacement has improved the survival of patients with MFS. Elective root replacement carries very low mortality and morbidity. Emergency root replacement for dissection is accompanied with higher early mortality and late deaths/interventions. Both the techniques of aortic root replacement, total root replacement (TRR) with a prosthetic valved conduit, and valve-sparing root replacement (VSRR) yield excellent early and late results. Considering the low risk of prosthetic valve-related events, the improved long-term survival, and event-free survival, TRR continues to be a very effective surgical option. VSSR also seems to be a good option for the first 10 to 15 years following surgery in MFS patients. The choice of procedure depends upon available expertise, patients' choice, feasibility of anticoagulation, possibility of pregnancy, and lifestyle of the patient. Aortic root morphology and state of valve cusps also affect the decision making. In recent times, personalized external aortic root support (PEARS) with a macroporous mesh sleeve has also emerged as a promising alternative to aortic root replacement. All these patients need close monitoring for whole life after surgical intervention.

Histopathological evaluation of aortic dissection: a comparison of congenital versus acquired aortic wall weakness

OBJECTIVES

The aim of this study was to identify pathological changes of aortic dissection based on histopathological evaluation of aortic wall weakness by comparing patients with and without congenital abnormalities.

METHODS

We reviewed records of patients who underwent repair for dissection-related aortic disease between 2008 and 2015. Fifty patients (20 men and 30 women; mean age 66.9 ± 14.0 years) who underwent surgery with subsequent histopathological examination of the aortic wall were divided into 2 groups. Group 1 had congenital abnormalities, including Marfan syndrome and bicuspid aortic valve (n = 5), and Group 2 had no congenital abnormalities (n = 45). We compared the histopathological characteristics of the aortic wall in these patients.

RESULTS

There were significant differences in age and body surface area between the 2 groups. Although 80% of Group 1 patients developed dissection at the middle of the media, all Group 2 patients developed dissection at the outer one-third of the media, which is along the pathway of the vasa vasorum of the aortic wall. Both groups showed the same extent of degeneration of the vasa vasorum. Group 1 showed a severe score of mucoid extracellular matrix accumulation in the aortic media.

CONCLUSIONS

Although it may be multifactorial, congenital maldevelopment of the media tends to result in dissection of the centre of the media, and acquired aortic wall weakness is concentrated in the outer third of the media. Degeneration of the vasa vasorum may be an important emerging substrate for developing aortic dissection.

Seno-destructive smooth muscle cells in the ascending aorta of patients with bicuspid aortic valve disease

Background

Ascending aortic aneurysms constitute an important hazard for individuals with a bicuspid aortic valve (BAV). However, the processes that degrade the aortic wall in BAV disease remain poorly understood.

Methods

We undertook in situ analysis of ascending aortas from 68 patients, seeking potentially damaging cellular senescence cascades. Aortas were assessed for senescence-associated-ß-galactosidase activity, p16^Ink4a and p21 expression, and double-strand DNA breaks. The senescence-associated secretory phenotype (SASP) of cultured-aged BAV aortic smooth muscle cells (SMCs) was evaluated by transcript profiling and consequences probed by combined immunofluorescence and circular polarization microscopy. The contribution of p38 MAPK signaling was assessed by immunostaining and blocking strategies.

Findings

We uncovered SMCs at varying depths of cellular senescence within BAV- and tricuspid aortic valve (TAV)-associated aortic aneurysms. Senescent SMCs were also abundant in non-aneurysmal BAV aortas but not in non-aneurysmal TAV aortas. Multivariable analysis revealed that BAV disease independently associated with SMC senescence. Furthermre, SMC senescence was heightened at the convexity of aortas associated with right-left coronary cusp fusion. Aged BAV SMCs had a pronounced collagenolytic SASP. Moreover, senescent SMCs in the aortic wall were enriched with surface-localized MMP1 and surrounded by weakly birefringent collagen fibrils. The senescent-collagenolytic SMC phenotype depended on p38 MAPK signaling, which was chronically activated in BAV aortas.

Interpretation

We have identified a cellular senescence-collagen destruction axis in at-risk ascending aortas. This novel “seno-destructive” SMC phenotype could open new opportunities for managing BAV aortopathy.

Fund

Canadian Institutes of Health Research, Lawson Health Research Institute, Heart and Stroke Foundation of Ontario/Barnett-Ivey Chair.

An Exploratory Look at Bicuspid Aortic Valve (Bav) Aortopathy: Focus on Molecular and Cellular Mechanisms

Bicuspid aortic valve (BAV) is the most common congenital heart malformation. BAV patients are at increased risk for aortic valve disease (stenosis/regurgitation), infective endocarditis, thrombi formation and, in particular, aortic dilatation, aneurysm and dissection. This review aims at exploring the possible interplay among genetics, extracellular matrix remodeling, abnormal signaling pathways, oxidative stress and inflammation in contributing to BAV-associated aortopathy (BAV-A-A). Novel circulating biomarkers have been proposed as diagnostic tools able to improve risk stratification in BAV-A-A. However, to date, the precise molecular and cellular mechanisms that lead to BAV-A-A remain unknown. Genetic, hemodynamic and cardiovascular risk factors have been implicated in the development and progression of BAV-A-A. Oxidative stress may also play a role, similarly to what observed in atherosclerosis and vulnerable plaque formation. The identification of common pathways between these 2 conditions may provide a platform for future therapeutic solutions.

Aortic Wall Elastic Properties in Case of Bicuspid Aortic Valve

Purpose of the Review

Bicuspid aortic valve (BAV) is associated with a significant risk of development of aneurysm and dissection of the ascending thoracic aorta. Development of what is called BAV associated aortopathy is particularly heterogeneous with an uncertain prognosis and with no prognostic biomarkers except for the aortic diameter. This situation leads to an important variability of the therapeutic strategy of this aortopathy. By reviewing the literature on aortic stiffness in the case of BAV, we aimed at evaluating its potential prognostic role in the development of aortic dilatation.

Recent Findings

Studies evaluating aortic stiffness, with ultrasound or magnetic resonance imaging, converge toward the description of an increased segmental aortic stiffness in BAV patients regardless of age, diameter or aortic level, from the root to the arch. Even though there is a lack of longitudinal studies evaluating the progression of aortic dilatation, new data have recently shown the potential prognostic role of the maximal rate of systolic distension of the aortic wall with magnetic resonance imaging.

Summary

Although the use of aortic distensibility calculation is a simple evaluation of stiffness that could be easily transposed in daily practice, its interpretation remains uncertain. New arterial stiffening indicators seem more promising but need a stronger validation.

The role of hemodynamics in bicuspid aortopathy: a histopathologic study

BACKGROUND

A bicuspid aortic valve (BAV) is the most common congenital cardiac malformation and is associated with ascending aortic dilation in 60%-80% of patients. In this study, we aimed to address the role of hemodynamic influences on the development of aortopathy in BAV patients.

PATIENT AND METHODS

BAV (n=36) and tricuspid aortic valve (TAV) patients (n=17) undergoing aortic valve replacement underwent preoperative flow magnetic resonance imaging (MRI) assessment to detect the area of maximal flow-induced stress in the proximal aorta. Based on these MRI data, paired ascending aortic wall samples [i.e., area of maximal jet impact (jet sample) and the opposite aortic wall (nonjet sample)] were collected during surgery. To study and describe the effects of jet stream on the complete vascular wall, a pathology score was developed based on the recently published aortic consensus paper statement on surgical pathology of the aorta using routine histologic stainings (resorcin fuchsin, hematoxylin-eosin, and Movat) and immunohistochemistry (alpha smooth muscle actin, smooth muscle 22 alpha, platelet endothelial cell adhesion molecule).

RESULTS

Comparing the jet and nonjet samples in both BAV and TAV, regions of maximal jet impact did not show any difference in the pathology score in the adventitia and the middle and outer media. In the jet samples, the inner media however showed loss of actin expression in both BAV (P<.0001) and the TAV (P=.0074), and the intimal thickness was significantly enlarged in both patient groups (BAV P=.0005, TAV P=.0041), which was not accompanied by loss of elastic lamellae or vascular smooth muscle cell nuclei.

CONCLUSIONS

In our study population, we could not demonstrate a potential distinct role for hemodynamics in the development of aortopathy in BAV patients even if corrected for aortic diameter, raphe position, or whether the valve is stenotic or regurgitant. The intimal layer and inner media however showed alterations in all jet specimens.

The Potential Beneficial Effects of Resveratrol on Cardiovascular Complications in Marfan Syndrome Patients⁻Insights from Rodent-Based Animal Studies

Marfan syndrome (MFS) patients are at risk for cardiovascular disease. In particular, for aortic aneurysm formation, which ultimately can result in a life-threatening aortic dissection or rupture. Over the years, research into a sufficient pharmacological treatment option against aortopathy has expanded, mostly due to the development of rodent disease models for aneurysm formation and dissections. Unfortunately, no optimal treatment strategy has yet been identified for MFS. The biologically-potent polyphenol resveratrol (RES), that occurs in nuts, plants, and the skin of grapes, was shown to have a positive effect on aortic repair in various rodent aneurysm models. RES demonstrated to affect aortic integrity and aortic dilatation. The beneficial processes relevant for MFS included the improvement of endothelial dysfunction, extracellular matrix degradation, and smooth muscle cell death. For the wide range of beneficial effects on these mechanisms, evidence was found for the following involved pathways; alleviating oxidative stress (change in eNOS/iNOS balance and decrease in NOX4), reducing protease activity to preserve the extracellular matrix (decrease in MMP2), and improving smooth muscle cell survival affecting aortic aging (changing the miR21/miR29 balance). Besides aortic features, MFS patients may also suffer from manifestations concerning the heart, such as mitral valve prolapse and left ventricular impairment, where evidence from rodent models shows that RES may aid in promoting cardiomyocyte survival directly (SIRT1 activation) or by reducing oxidative stress (increasing superoxide dismutase) and increasing autophagy (AMPK activation). This overview discusses recent RES studies in animal models of aortic aneurysm formation and heart failure, where different advantageous effects have been reported that may collectively improve the aortic and cardiac pathology in patients with MFS. Therefore, a clinical study with RES in MFS patients seems justified, to validate RES effectiveness, and to judge its suitability as potential new treatment strategy.

Enlightening the Association between Bicuspid Aortic Valve and Aortopathy

Bicuspid aortic valve (BAV) patients have an increased incidence of developing aortic dilation. Despite its importance, the pathogenesis of aortopathy in BAV is still largely undetermined. Nowadays, intense focus falls both on BAV morphology and progression of valvular dysfunction and on the development of aortic dilation. However, less is known about the relationship between aortic valve morphology and aortic dilation. A better understanding of the molecular pathways involved in the homeostasis of the aortic wall, including the extracellular matrix, the plasticity of the vascular smooth cells, TGFβ signaling, and epigenetic dysregulation, is key to enlighten the mechanisms underpinning BAV-aortopathy development and progression. To date, there are two main theories on this subject, i.e., the genetic and the hemodynamic theory, with an ongoing debate over the pathogenesis of BAV-aortopathy. Furthermore, the lack of early detection biomarkers leads to challenges in the management of patients affected by BAV-aortopathy. Here, we critically review the current knowledge on the driving mechanisms of BAV-aortopathy together with the current clinical management and lack of available biomarkers allowing for early detection and better treatment optimization.

Participation of Arachidonic Acid Metabolism in the Aortic Aneurysm Formation in Patients with Marfan Syndrome

Marfan syndrome (MFS) is a pleiotropic genetic disease involving the cardiovascular system where a fibrillin-1 mutation is present. This mutation is associated with accelerated activation of transforming growth factor β (TGFβ1) which contributes to the formation of aneurysms in the root of the aorta. There is an imbalance in the synthesis of thromboxane A₂ (TXA₂) and prostacyclin, that is a consequence of a differential protein expression of the isoforms of cyclooxygenases (COXs), suggesting an alteration of arachidonic acid (AA) metabolism. The aim of this study was to analyze the participation of AA metabolism associated with inflammatory factors in the dilation and dissection of the aortic aneurysm in patients with MFS. A decrease in AA (p = 0.02), an increase in oleic acid (OA), TGFβ1, tumor necrosis factor alpha (TNFα), prostaglandin E₂ (PGE₂) (p < 0.05), and COXs activity (p = 0.002) was found. The expressions of phospholipase A₂ (PLA₂), cytochrome P450 (CYP450 4A), 5-lipoxygenase (5-LOX), COX2 and TXA2R (p < 0.05) showed a significant increase in the aortic aneurysm of patients with MFS compared to control subjects. COX1, 6-keto-prostaglandin 1 alpha (6-keto-PG_1α) and 8-isoprostane did not show significant changes. Histological examination of the aortas showed an increase of cystic necrosis, elastic fibers and collagen in MFS. The results suggest that there are inflammatory factors coupled to genetic factors that predispose to aortic endothelial dysfunction in the aortic tissue of patients with MFS. There is a decrease in the percentage of AA, associated with an increase of PLA₂, COX2/TXA2R, CYP450 4A, and 5-LOX which leads to a greater synthesis of PGE₂ than of 6-keto-PGF_1α, thus contributing to the formation of the aortic aneurysm. The evident loss of the homeostasis in these mechanisms confirms that there is a participation of the AA pathway in the aneurysm progression in MFS.

Pathogenesis of aortic wall complications in Marfan syndrome

BACKGROUND

Patients with Marfan (MFS) syndrome and patients with a bicuspid aortic valve (BAV) are more prone to develop aortic dilation and dissection compared to persons with a tricuspid aortic valve (TAV). To elucidate potential common as well as distinct pathways of clinical relevance, we compared the histopathological substrates of aortic pathology.

PATIENT AND METHODS

Ascending aortic wall specimen were divided in five groups: BAV (n=36) and TAV (n=23) without and with dilation and non-dilated MFS (n=8). We performed routine histology to study aortic wall features based on the aortic consensus statement. Immunohistological markers for vascular smooth muscle cell (VSMC) maturation, and expression of fibrillin-1 were additionally investigated for the underlying pathogenesis.

RESULTS

On basis of the routine histology the aorta in MFS was similar to the aorta in dilated TAVs (overall medial degeneration, elastic fiber fragmentation, loss and disorganization, , and VSMC nuclei loss). The other markers aided in clustering the MFS and BAV patients with a significantly lower fibrillin-1 expression as compared to the TAVs (p<0.05), a lower level of differentiated VSMC markers (p<0.05) and elastic fiber thinning.

CONCLUSIONS

Pathogenesis of aortopathy in MFS overlaps with mechanisms seen in BAV and TAV, leading to a so called double hit hypothesis for aortic complications in MFS. The ascending aortic wall in MFS is immature with undifferentiated VSMCs and low levels of fibrillin-1. The immature media becomes even more vulnerable for aortopathy due to other degenerative features which develop probably as a direct consequence of the fibrillin-1 mutation.

Biomechanical properties of the thoracic aorta in Marfan patients

Background

Marfan syndrome (MFS), a genetic disorder of the connective tissue, has been strongly linked to dilation of the thoracic aorta, among other cardiovascular complications. As a result, MFS patients frequently suffer from aortic dissection and rupture, contributing to the high rate of mortality and morbidity among MFS patients. Despite the significant effort devoted to the investigation of mechanical and structural properties of aneurysmal tissue, studies on Marfan aneurysmal biomechanics are scarce. Ex vivo mechanical characterization of MFS aneurysmal tissue can provide a better insight into tissue strength outside the physiologic loading range and serve as a basis for improved risk assessment and failure prediction.

Methods

The mechanical and microstructural properties of MFS aneurysmal thoracic aorta (MFS, n=15, 39.5±3.91 years), non-MFS aneurysmal thoracic aorta (TAA, n=8, 52.8±4.9 years), healthy human thoracic aorta (HH, n=8, 75.4±6.1 years), and porcine thoracic aorta (n=10) are investigated. Planar biaxial tensile testing and uniaxial failure testing were utilized to characterize the mechanical and failure properties of the tissue, respectively. Verhoeff-Van Gieson (VVG) and PicroSirius Red stains were utilized to visualize the elastin and collagen fiber architecture, respectively.

Results

MFS tissue was found to have age-dependent but diameter-independent mechanical, structural, and morphological properties, also showing extensive elastin fiber degradation. Non-MFS thoracic aneurysmal aorta was thicker and stiffer than age-matched MFS tissue. Moreover, non-MFS thoracic aneurysmal mechanics resembled closely the mechanics of older healthy human tissue. Younger MFS tissue (<40 years) exhibited similar mechanical and structural properties to aged porcine tissue.

Conclusions

Both age and aneurysmal presence were found to be factors associated with increased stiffness in aortic tissue, and aortic diameter was not a significant determinant of mechanical property deterioration. Additionally, the presence of MFS was found to induce stiffening of the thoracic aorta, although not to the extent of the non-MFS aneurysm.

Metabolomic profiling of ascending thoracic aortic aneurysms and dissections - Implications for pathophysiology and biomarker discovery

Objective

Our basic understanding of ascending thoracic aortic aneurysm (ATAA) pathogenesis is still very limited, hampering early diagnosis, risk prediction, and development of treatment options. “Omics”-technologies, ideal to reveal tissue alterations from the normal physiological state due to disease have hardly been applied in the field. Using a metabolomic approach, with this study the authors seek to define tissue differences between controls and various forms of ATAAs.

Methods

Using a targeted FIA-MS/MS metabolomics approach, we analysed and compared the metabolic profiles of ascending thoracic aortic wall tissue of age-matched controls (n = 8), bicuspid aortic valve-associated aneurysms (BAV-A; n = 9), tricuspid aortic valve-associated aneurysms (TAV-A; n = 14), and tricuspid aortic valve-associated aortic dissections (TAV-Diss; n = 6).

Results

With sphingomyelin (SM) (OH) C22:2, SM C18:1, SM C22:1, and SM C24:1 only 4 out of 92 detectable metabolites differed significantly between controls and BAV-A samples. Between controls and TAV-Diss samples only phosphatidylcholine (PC) ae C32:1 differed. Importantly, our analyses revealed a general increase in the amount of total sphingomyelin levels in BAV-A and TAV-Diss samples compared to controls.

Conclusions

Significantly increased levels of sphingomyelins in BAV-A and TAV-Diss samples compared to controls may argue for a repression of sphingomyelinase activity and the sphingomyelinase-ceramide pathway, which may result in an inhibition of tissue regeneration; a potential basis for disease initiation and progression.

Year in review: bicuspid aortopathy

PURPOSE OF REVIEW

This article outlines the key research contribution to bicuspid aortic valve (BAV) aortopathy over the past 18 months.

RECENT FINDINGS

Investigators have further defined the current gaps in knowledge and the scope of the clinical problem of BAV aortopathy. Support for aggressive resection strategies is waning as evidence mounts to suggest that BAV is not similar to genetic connective tissue disorders with respect to aortic risks. The role of cusp fusion patterns and valve-mediated hemodynamics in disease progression is a major area of discovery. Molecular and cellular mechanisms remain elusive and contradictory.

SUMMARY

BAV aortopathy is a major public health problem that remains poorly understood. New insights on valve-mediated hemodynamics using novel imaging modalities may lead to more individualized resection strategies and improved clinical guidelines.

Marfan syndrome associated aortic disease in neonates and children: a clinical-morphologic review

BACKGROUND

Marfan syndrome (MFS) is a multisystem connective tissue disorder that can lead to aortic dilation requiring aortic root replacement. Neonatal MFS (nMFS) is a rare and severe form of MFS compared to classic MFS (cMFS). Aortic root histology in MFS is thought to demonstrate predominantly medial degeneration (MD) of a translamellar mucoid extracellular matrix accumulation (MEMA-T) vs. the intralamellar mucoid extracellular matrix accumulation (MEMA-I) seen in other aortopathies. The objective of this study was to describe the clinical and histopathologic features of nMFS and cMFS patients undergoing aortic root replacement.

METHODS

Children with MFS who underwent aortic root replacement between 2000 and 2012 at a single institution were included. Medical records including clinical details, aortic dimensions (Z scores), and histology including MD type were obtained. Statistics were descriptive with univariate analysis of age at surgery and type of MD.

RESULTS

Eleven patients, 3 (27%) with nMFS, were included. Root dilation at time of surgery was greater in nMFS compared to cMFS (Z=12.8 vs. 7.6, P=.005), and nMFS patients were younger at time of surgery (7.3 vs. 18.8 years, P=.002). Histology in the nMFS group demonstrated MEMA-I in one and no MD in two. In the cMFS group, there were three with MEMA-T, four with MEMA-I, and one with both types.

CONCLUSION

In summary, nMFS has earlier root dilation often in the absence of MD. Both forms of MD were present in our cohort, and there was no correlation between age at surgery and type of MD.

Generation and Characterization of Vascular Smooth Muscle Cell Lines Derived from a Patient with a Bicuspid Aortic Valve

Thoracic aortic dilation is the most common malformation of the proximal aorta and is responsible for 1%-2% of all deaths in industrialized countries. In approximately 50% of patients with a bicuspid aortic valve (BAV), dilation of any or all segments of the aorta occurs. BAV patients with aortic dilation show an increased incidence of cultured vascular smooth muscle cell (VSMC) loss. In this study, VSMC, isolated from the ascending aorta of BAV, was treated with Simian virus 40 to generate a BAV-originated VSMC cell line. To exclude any genomic DNA or cross-contamination, highly polymorphic short tandem repeats of the cells were profiled. The cells were then characterized using flow cytometry and karyotyping. The WG-59 cell line created is the first reported VSMC cell line isolated from a BAV patient. Using an RT² Profiler PCR Array, genes within the TGFβ/BMP family that are dependent on losartan treatment were identified. Endoglin was found to be among the regulated genes and was downregulated in WG-59 cells following treatment with different losartan concentrations, when compared to untreated WG-59 cells.

Variable severity of cardiovascular phenotypes in patients with an early-onset form of Marfan syndrome harboring FBN1 mutations in exons 24-32

A subgroup of patients with Marfan syndrome (MFS) who have mutations in exons 24-32 of the FBN1 gene manifests severe atrioventricular valve insufficiency and skeletal problems as early as the neonatal period. These patients usually die in the first 2 years of life, thus a region between exons 24 and 32 of FBN1 is recognized as a critical region for this neonatal form of MFS (nMFS). Here, we report five consecutive patients who manifested a cardiovascular phenotype until infancy with mutations in the critical region for nMFS. Although three of these patients showed severe mitral regurgitation and died before reaching 1 year of age, the remaining two patients survived for over 5 years under medical and/or surgical interventions. Two splicing mutations and one missense mutation were identified in the three deceased patients, whereas two missense mutations were found in the two survivors. Currently, the clinical severity of patients with early-onset MFS harboring mutations in the critical region for nMFS seem to be more variable than ever thought, and intensive treatments are recommended even in this subgroup of patients with MFS.