Rationale and design of a randomized clinical trial (Marfan Sartan) of angiotensin II receptor blocker therapy versus placebo in individuals with Marfan syndrome

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.

Cooperative Mechanism of ADAMTS/ ADAMTSL and Fibrillin-1 in the Marfan Syndrome and Acromelic Dysplasias

The term “fibrillinopathies” gathers various diseases with a wide spectrum of clinical features and severity but all share mutations in the fibrillin genes. The first described fibrillinopathy, Marfan syndrome (MFS), is a multisystem disease with a unique combination of skeletal, thoracic aortic aneurysm (TAA) and ocular features. The numerous FBN1 mutations identified in MFS are located all along the gene, leading to the same pathogenic mechanism. The geleophysic/acromicric dysplasias (GD/AD), characterized by short stature, short extremities, and joint limitation are described as “the mirror image” of MFS. Previously, in GD/AD patients, we identified heterozygous FBN1 mutations all affecting TGFβ-binding protein-like domain 5 (TB5). ADAMTS10, ADAMTS17 and, ADAMTSL2 are also involved in the pathogenic mechanism of acromelic dysplasia. More recently, in TAA patients, we identified mutations in THSD4, encoding ADAMTSL6, a protein belonging to the ADAMTSL family suggesting that ADAMTSL proteins are also involved in the Marfanoid spectrum. Together with human genetic data and generated knockout mouse models targeting the involved genes, we provide herein an overview of the role of fibrillin-1 in opposite phenotypes. Finally, we will decipher the potential biological cooperation of ADAMTS-fibrillin-1 involved in these opposite phenotypes.

Loeys-Dietz Syndrome

Loeys-Dietz syndrome is an autosomal dominant aortic aneurysm syndrome characterized by multisystemic involvement. The most typical clinical triad includes hypertelorism, bifid uvula or cleft palate and aortic aneurysm with tortuosity. Natural history is significant for aortic dissection at smaller aortic diameter and arterial aneurysms throughout the arterial tree. The genetic cause is heterogeneous and includes mutations in genes encoding for components of the transforming growth factor beta (TGFβ) signalling pathway: TGFBR1, TGFBR2, SMAD2, SMAD3, TGFB2 and TGFB3. Despite the loss of function nature of these mutations, the patient-derived aortic tissues show evidence of increased (rather than decreased) TGFβ signalling. These insights offer new options for therapeutic interventions.

Nitric oxide in the Marfan vasculature: Friend or foe?

Marfan syndrome (MFS) is a connective tissue disorder caused by mutations in the FBN1 gene, which encodes fibrillin-1, a protein essential for the formation and stabilization of elastic fibers as well as signaling homeostasis. Progressive aortic root widening is the most serious manifestation of MFS as it can lead to aortic dissection, aneurysm formation and rupture. However, despite their ability to decrease the hemodynamic stress the aorta is subjected to, anti-hypertensive medications often lead to underwhelming reductions in the rate of aortic root dilation, which illustrates how fragmental our understanding of MFS-associated aortic remodeling is. This manuscript summarizes recent evidence that document nitric oxide (NO) synthase (NOS)-related changes to the vasculature during the pathogenesis of MFS and how they result in a unique state of vascular dysfunction that likely plays a causal role in the aortic root widening process. We also review how clinic-approved and experimental therapies as well lifestyle approaches may promote aortic root stability by correcting NO homeostasis, which if properly optimized may improve outcomes in this population afflicted by a notoriously refractory type of aortopathy.

Smooth Muscle α-Actin Expression in Mitral Valve Interstitial Cells is Important for Mediating Extracellular Matrix Remodeling

Background: Mitral valve prolapse (MVP) affects 3–6% of the total population including those with connective tissue disorders. Treatment is limited, and patients commonly require surgery which can be impermanent and insuperable. Abnormal prolapse of mitral valve leaflets into the left atria is caused by disturbances to the composition and organization of the extracellular matrix (ECM), that weaken biomechanics. This process, known as myxomatous degeneration is characterized by an abnormal accumulation of proteoglycans, in addition to collagen fiber disruption and elastic fiber fragmentation. The underlying mechanisms that promote myxomatous degeneration to the point of biomechanical failure are unknown, but previous histological studies of end-stage diseased tissue have reported abnormal α-smooth muscle actin (SMA) in a subset of heart valve interstitial cells (VICs); however, the contribution of these abnormal cells to MVP pathogenesis has not been extensively examined. Methods: In vivo and in vitro approaches were used. Mice harboring a Fbn1^C1039G mutation mimic human Marfan Syndrome and develop MVP. Using these mice, temporal and spatial changes in SMA expression relative to myxomatous degeneration were examined using histological techniques. In parallel in vitro experiments, SMA expression was downregulated in primary porcine mitral VICs directly using siRNA, and indirectly using the actin depolymerizing agent Latrunculin A. In addition, the regulation of SMA in VICs by mechanical stiffness was explored relative to ECM remodeling. Results: We show, in mitral valves from Fbn1^C1039G/+ mice, that abnormal increases in SMA expression in VICs are evident during early postnatal stages of disease, prior to significant myxomatous degeneration as indicated at later stages by increased proteoglycans and collagen type I (Col1a1). Furthermore, abnormal SMA expression continues to increase during the course of pathogenesis and is localized to the mid belly region of the mitral valve leaflets from 10 weeks. Using an in vitro approach, we demonstrate that reduced SMA function by direct siRNA or indirect Latrunculin A treatment attenuates proteoglycan and Col1a1 expression in porcine mitral VICs. While upstream, we provide insights to show that SMA is regulated by mechanical tension in VICs to promote changes in ECM homeostasis. Conclusions: Together, our data show that in VICs, SMA, an actin binding protein, is important for mediating ECM remodeling associated with phenotypes observed in myxomatous degeneration, and its expression is regulated by mechanical tension. These novel insights could inform the development of future non-surgical therapeutics to halt the progression of mitral valve degeneration thereby avoiding end-stage prolapse.

Progress toward a Glycoprotein VI Modulator for the Treatment of Thrombosis

Pathogenic thrombus formation accounts for the etiology of many serious conditions including myocardial infarction, stroke, deep vein thrombosis, and pulmonary embolism. Despite the development of numerous anticoagulants and antiplatelet agents, the mortality rate associated with these diseases remains high. In recent years, however, significant epidemiological evidence and clinical models have emerged to suggest that modulation of the glycoprotein VI (GPVI) platelet receptor could be harnessed as a novel antiplatelet strategy. As such, many peptidic agents have been described in the past decade, while more recent efforts have focused on the development of small molecule modulators. Herein the rationale for targeting GPVI is summarized and the published GPVI modulators are reviewed, with particular focus on small molecules. A qualitative pharmacophore hypothesis for small molecule ligands at GPVI is also presented.

[Dental-craniofacial manifestation and treatment of rare diseases in China]

Rare diseases are genetic, chronic, and incurable disorders with relatively low prevalence. Thus, diagnosis and management strategies for such diseases are currently limited. This situation is exacerbated by insufficient medical sources for these diseases. The National Health and Health Committee of China recently first provided a clear definition of 121 rare diseases in the Chinese population. In this study, we summarize several dental-craniofacial manifestations associated with some rare diseases to provide a reference for dentists and oral maxillofacial surgeons aiming at fast-tracking diagnosis for the management of these rare diseases.

Dental-craniofacial manifestation and treatment of rare diseases

Rare diseases are usually genetic, chronic and incurable disorders with a relatively low incidence. Developments in the diagnosis and management of rare diseases have been relatively slow due to a lack of sufficient profit motivation and market to attract research by companies. However, due to the attention of government and society as well as economic development, rare diseases have been gradually become an increasing concern. As several dental-craniofacial manifestations are associated with rare diseases, we summarize them in this study to help dentists and oral maxillofacial surgeons provide an early diagnosis and subsequent management for patients with these rare diseases.

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.

Marfan syndrome: current perspectives

Marfan syndrome (MFS) is a pleiotropic connective tissue disease inherited as an autosomal dominant trait, due to mutations in the FBN1 gene encoding fibrillin 1. It is an important protein of the extracellular matrix that contributes to the final structure of a microfibril. Few cases displaying an autosomal recessive transmission are reported in the world. The FBN1 gene, which is made of 66 exons, is located on chromosome 15q21.1. This review, after an introduction on the clinical manifestations that leads to the diagnosis of MFS, focuses on cardiovascular manifestations, pharmacological and surgical therapies of thoracic aortic aneurysm and/or dissection (TAAD), mechanisms underlying the progression of aneurysm or of acute dissection, and biomarkers associated with progression of TAADs. A Dutch group compared treatment with losartan, an angiotensin II receptor-1 blocker, vs no other additional treatment (COMPARE clinical trial). They observed that losartan reduces the aortic dilatation rate in patients with Marfan syndrome. Later on, they also reported that losartan exerts a beneficial effect on patients with Marfan syndrome carrying an FBN1 mutation that causes haploinsufficiency (quantitative mutation), while it has no significant effect on patients displaying dominant negative (qualitative) mutations. Moreover, a French group in a 3-year trial compared the administration of losartan vs placebo in patients with Marfan syndrome under treatment with beta-receptor blockers. They observed that losartan decreases blood pressure but has no effect on aortic diameter progression. Thus, beta-receptor blockers remain the gold standard therapy in patients with Marfan syndrome. Three potential biochemical markers are mentioned in this review: total homocysteine, serum transforming growth factor beta, and lysyl oxidase. Moreover, markers of oxidative stress measured in plasma, previously correlated with clinical features of Marfan syndrome, may be explored as potential biomarkers of clinical severity.

The effect of losartan on progressive aortic dilatation in patients with Marfan's syndrome: a meta-analysis of prospective randomized clinical trials

OBJECTIVE

To assess the effect of losartan therapy on progressive aortic dilatation and on clinical outcome in patients with Marfan's syndrome (MFS).

METHODS

The meta-analysis was instituted, which included studies identified by a systematic review of MEDLINE of peer-reviewed publications. Echocardiogram or MRI measurements of the aortic root dimension and outcome measures of death, cardiovascular surgery and aortic dissection or rupture were compared between patients who were treated and untreated with losartan therapy.

RESULTS

Six randomized trials with 1398 subjects met all the inclusion criteria and were included in the meta-analysis. Compared with non-losartan treatment, losartan therapy significantly decreased the rate of aortic dilatation (SMD=-0.13 with 95% CI -0.25 to 0.00, p=0.04). The clinical outcome beneficial was not observed in the losartan treatment group when compared with no losartan treatment group (odds ratio=1.04 with 95% CI of 0.57-1.87).

CONCLUSION

Given the current results of the meta-analysis and together with the lack of associated side effects, it would be reasonable to use losartan in MFS patients with aortic root dilatation. However, no clinical outcome benefits were observed in the losartan treatment group when compared with no losartan treatment group.

Losartan and captopril treatment rescue normal thrombus formation in microfibril associated glycoprotein-1 (MAGP1) deficient mice

INTRODUCTION

MAGP1 is a glycoprotein present in the elastic fibers and is a part of the microfibrils components. MAGP1 interacts with von Willebrand factor and the active form of TGF-β and BMP. In mice lacking MAGP1, thrombus formation is delayed, increasing the occlusion time of carotid artery despite presenting normal blood coagulation in vitro. MAGP1-containing microfibrils may play a role in hemostasis and thrombosis. In this work, we evaluated the function of MAGP1 and its relation to TGF-β in the arterial thrombosis process.

METHODS AND RESULTS

We analyzed thrombus formation time in wild type and MAGP1-deficient mice comparing Rose Bengal and Ferric Chloride induced arterial lesion. The potential participation of TGF-β in this process was accessed when we treated both wild type and MAGP1-deficient mice with losartan (an antihypertensive drug that decreases TGF-β activity) or captopril (an angiotensin converting enzyme inhibitor that was used as a control antihypertensive drug). Besides, we evaluated thrombus embolization and the gelatinolytic activity in the arterial walls in vitro and ex vivo. Losartan and captopril were able to recover the thrombus formation time without changing blood pressure, activated partial thromboplastin time (aPTT), PT (prothrombin time), platelet aggregation and adhesion, but decreased gelatinase activity.

CONCLUSIONS

Our results suggest that both treatments are effective in the prevention of the sub-endothelial ECM degradation, allowing the recovery of normal thrombus formation.

Recent Clinical Drug Trials Evidence in Marfan Syndrome and Clinical Implications

Marfan syndrome is a genetic disorder of connective tissue with principal manifestations in the cardiovascular, ocular, and skeletal systems. Cardiovascular disease, mainly progressive aortic root dilation and aortic dissection, is the leading cause of morbidity and mortality. The primary aims of this report were to examine the evidence related to medical therapy for Marfan syndrome, including recently completed randomized clinical trials on the efficacy of β-blockers and angiotensin II receptor blockers for the prophylactic treatment of aortic enlargement in Marfan syndrome, and to provide recommendations for medical therapy on the basis of available evidence. Medical therapy for Marfan syndrome should be individualized according to patient tolerance and risk factors such as age, aortic size, and family history of aortic dissection. The Pediatric Heart Network trial showed that atenolol and losartan each reduced the rate of aortic dilation. All patients with known or suspected Marfan syndrome and aortic root dilation should receive medical therapy with adequate doses of either β-blocker or angiotensin receptor blocker. The Pediatric Heart Network trial also showed that atenolol and losartan are more effective at reduction of aortic root z score in younger subjects, which suggests that medical therapy should be prescribed even in the youngest children with aortic dilation. For patients with Marfan syndrome without aortic dilation, the available evidence is less clear. If aortic dilation is severe and/or progressive, therapy with a combination of β-blocker and angiotensin receptor blocker should be considered, although trial results are mixed with respect to the efficacy of combination therapy vs monotherapy.

Fibrillin-containing microfibrils are key signal relay stations for cell function

Fibrillins constitute the backbone of microfibrils in the extracellular matrix of elastic and non-elastic tissues. Mutations in fibrillins are associated with a wide range of connective tissue disorders, the most common is Marfan syndrome. Microfibrils are on one hand important for structural stability in some tissues. On the other hand, microfibrils are increasingly recognized as critical mediators and drivers of cellular signaling. This review focuses on the signaling mechanisms initiated by fibrillins and microfibrils, which are often dysregulated in fibrillin-associated disorders. Fibrillins regulate the storage and bioavailability of growth factors of the TGF-β superfamily. Cells sense microfibrils through integrins and other receptors. Fibrillins potently regulate pathways of the immune response, inflammation and tissue homeostasis. Emerging evidence show the involvement of microRNAs in disorders caused by fibrillin deficiency. A thorough understanding of fibrillin-mediated cell signaling pathways will provide important new leads for therapeutic approaches of the underlying disorders.

Medical treatment of aortic aneurysms in Marfan syndrome and other heritable conditions

Thoracic aortic aneurysms can be triggered by genetic disorders such as Marfan syndrome (MFS) and related aortic diseases as well as by inflammatory disorders such as giant cell arteritis or atherosclerosis. In all these conditions, cardiovascular risk factors, such as systemic arterial hypertension, may contribute to faster rate of aneurysm progression. Optimal medical management to prevent progressive aortic dilatation and aortic dissection is unknown. β-blockers have been the mainstay of medical treatment for many years despite limited evidence of beneficial effects. Recently, losartan, an angiotensin II type I receptor antagonist (ARB), has shown promising results in a mouse model of MFS and subsequently in humans with MFS and hence is increasingly used. Several ongoing trials comparing losartan to β-blockers and/or placebo will better define the role of ARBs in the near future. In addition, other medications, such as statins and tetracyclines have demonstrated potential benefit in experimental aortic aneurysm studies. Given the advances in our understanding of molecular mechanisms triggering aortic dilatation and dissection, individualized management tailored to the underlying genetic defect may be on the horizon of individualized medicine. We anticipate that ongoing research will address the question whether such genotype/pathogenesis-driven treatments can replace current phenotype/syndrome-driven strategies and whether other forms of aortopathies should be treated similarly. In this work, we review currently used and promising medical treatment options for patients with heritable aortic aneurysmal disorders.

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

Patients with bicuspid aortic valve (BAV) and patients with Marfan syndrome (MFS) are more prone to develop aortic dilation and dissection compared to persons with a tricuspid aortic valve (TAV). To elucidate potential common and distinct pathways of clinical relevance, we compared the histopathological substrates of aortopathy. Ascending aortic wall biopsies were divided in five groups: BAV (n = 36) and TAV (n = 23) without and with dilation and non-dilated MFS (n = 8). General histologic features, apoptosis, the expression of markers for vascular smooth muscle cell (VSMC) maturation, markers predictive for ascending aortic dilation in BAV, and expression of fibrillin-1 were investigated. Both MFS and BAV showed an altered distribution and decreased fibrillin-1 expression in the aorta and a significantly lower level of differentiated VSMC markers. Interestingly, markers predictive for aortic dilation in BAV were not expressed in the MFS aorta. The aorta in MFS was similar to the aorta in dilated TAV with regard to the presence of medial degeneration and apoptosis, while other markers for degeneration and aging like inflammation and progerin expression were low in MFS, comparable to BAV. Both MFS and BAV aortas have immature VSMCs, while MFS and TAV patients have a similar increased rate of medial degeneration. However, the mechanism leading to apoptosis is expected to be different, being fibrillin-1 mutation induced increased angiotensin-receptor-pathway signaling in MFS and cardiovascular aging and increased progerin in TAV. Our findings could explain why angiotensin inhibition is successful in MFS and less effective in TAV and BAV patients.

Inhibition of Glycoprotein VI Clustering by Collagen as a Mechanism of Inhibiting Collagen-Induced Platelet Responses: The Example of Losartan

Exposure of platelets to collagen triggers the formation of a platelet clot. Pharmacological agents capable of inhibiting platelet activation by collagen are thus of potential therapeutic interest. Thrombus formation is initiated by the interaction of the GPIb-V-IX complex with collagen-bound vWF, while GPVI interaction with collagen triggers platelet activation that is reinforced by ADP and thromboxane A2. Losartan is an angiotensin II (Ang II) type I receptor (AT1R) antagonist proposed to have an antiplatelet activity via the inhibition of both the thromboxane A2 (TXA2) receptor (TP) and the glycoprotein VI (GPVI). Here, we characterized in vitro the effects of losartan at different doses on platelet responses: losartan inhibited platelet aggregation and secretion induced by 1 μg.mL^-1 and 10 μg.mL^-1 of collagen with an IC50 of ~ 6 μM. Losartan inhibited platelet responses induced by the GPVI specific collagen related peptide but not by the α2β1 specific peptide. However, losartan did not inhibit the binding of recombinant GPVI to collagen, which is not in favor of a simple competition. Indeed, the clustering of GPVI observed in flow cytometry and using the Duolink methodology, was inhibited by losartan. The impact of a therapeutic dose of losartan (100 mg/day) on platelet responses was analyzed ex vivo in a double blind study. No statistically significant differences were observed between losartan-treated (n=25) and non-treated (n=30) patients in terms of collagen and U46619-induced platelet activation. These data indicate that in treated patients, losartan does not achieve a measurable antiplatelet effect but provide the proof of concept that inhibiting collagen-induced GPVI clustering is of pharmacological interest to obtain an antithrombotic efficacy.

Design and rationale of a prospective, collaborative meta-analysis of all randomized controlled trials of angiotensin receptor antagonists in Marfan syndrome, based on individual patient data: A report from the Marfan Treatment Trialists' Collaboration

Rationale

A number of randomized trials are underway, which will address the effects of angiotensin receptor blockers (ARBs) on aortic root enlargement and a range of other end points in patients with Marfan syndrome. If individual participant data from these trials were to be combined, a meta-analysis of the resulting data, totaling approximately 2,300 patients, would allow estimation across a number of trials of the treatment effects both of ARB therapy and of β-blockade.

Such an analysis would also allow estimation of treatment effects in particular subgroups of patients on a range of end points of interest and would allow a more powerful estimate of the effects of these treatments on a composite end point of several clinical outcomes than would be available from any individual trial.

Design

A prospective, collaborative meta-analysis based on individual patient data from all randomized trials in Marfan syndrome of (i) ARBs versus placebo (or open-label control) and (ii) ARBs versus β-blockers will be performed.

A prospective study design, in which the principal hypotheses, trial eligibility criteria, analyses, and methods are specified in advance of the unblinding of the component trials, will help to limit bias owing to data-dependent emphasis on the results of particular trials. The use of individual patient data will allow for analysis of the effects of ARBs in particular patient subgroups and for time-to-event analysis for clinical outcomes.

The meta-analysis protocol summarized in this report was written on behalf of the Marfan Treatment Trialists' Collaboration and finalized in late 2012, without foreknowledge of the results of any component trial, and will be made available online (http://www.ctsu.ox.ac.uk/research/meta-trials).

Atenolol versus losartan in children and young adults with Marfan's syndrome

BACKGROUND

Aortic-root dissection is the leading cause of death in Marfan's syndrome. Studies suggest that with regard to slowing aortic-root enlargement, losartan may be more effective than beta-blockers, the current standard therapy in most centers.

METHODS

We conducted a randomized trial comparing losartan with atenolol in children and young adults with Marfan's syndrome. The primary outcome was the rate of aortic-root enlargement, expressed as the change in the maximum aortic-root-diameter z score indexed to body-surface area (hereafter, aortic-root z score) over a 3-year period. Secondary outcomes included the rate of change in the absolute diameter of the aortic root; the rate of change in aortic regurgitation; the time to aortic dissection, aortic-root surgery, or death; somatic growth; and the incidence of adverse events.

RESULTS

From January 2007 through February 2011, a total of 21 clinical centers enrolled 608 participants, 6 months to 25 years of age (mean [±SD] age, 11.5±6.5 years in the atenolol group and 11.0±6.2 years in the losartan group), who had an aortic-root z score greater than 3.0. The baseline-adjusted rate of change in the mean (±SE) aortic-root z score did not differ significantly between the atenolol group and the losartan group (-0.139±0.013 and -0.107±0.013 standard-deviation units per year, respectively; P=0.08). Both slopes were significantly less than zero, indicating a decrease in the aortic-root diameter relative to body-surface area with either treatment. The 3-year rates of aortic-root surgery, aortic dissection, death, and a composite of these events did not differ significantly between the two treatment groups.

CONCLUSIONS

Among children and young adults with Marfan's syndrome who were randomly assigned to losartan or atenolol, we found no significant difference in the rate of aortic-root dilatation between the two treatment groups over a 3-year period. (Funded by the National Heart, Lung, and Blood Institute and others; ClinicalTrials.gov number, NCT00429364.).

Angiotensin receptor blockers: a panacea for Marfan syndrome and related disorders?

The study of mouse models for Marfan syndrome, an autosomal dominant connective tissue disorder caused by mutations in fibrillin-1 (FBN1), has shifted our understanding of the pathogenesis of thoracic aortic aneurysm significantly. Multiple lines of evidence support the notion that dysregulation of canonical and noncanonical transforming growth factor (TGF)β signaling is the responsible pathway in this and related thoracic aortic aneurysm conditions. This exciting knowledge has opened numerous new treatment options, including antagonism of the angiotensin II receptor blocker type 1 (AT1R). In this review, we summarize the current knowledge, the first human losartan Marfan trial results and future therapeutic perspectives for aortic disease in Marfan patients.

Aortopathy in Marfan syndrome: an update

Marfan syndrome (MFS) is an inherited autosomal dominant multisystem disease caused by mutations in the FBN1 gene encoding fibrillin-1, an extracellular matrix glycoprotein widely distributed in mesenchymal-derived tissues that provide a scaffold for elastin deposition. MFS is characterized by variable clinical manifestations, including skeletal, ocular, and cardiovascular abnormalities; ascending aortic aneurysm with ensuing dissection and rupture is the main life-threatening cardiovascular manifestation of MFS. Histological aspects of MFS aortopathy include a medial degeneration from disarray and fragmentation of elastic fibers and accumulation of basophilic ground substance areas depleted of smooth muscle cells (SMCs). Transmission electron microscopy well evidences the high number of interruptions and the thick appearance of the elastic lamellae and the accumulation of abundant extracellular glycosaminoglycan-rich material, sometimes SMCs showing a prevalent synthetic phenotype. The aberrant signaling of transforming growth factor-β (TGF-β) as the consequence of the altered structure of fibrillin-1 induces activation and the overexpression of Smad-dependent profibrotic signaling pathway and ERK1/2-mediated increased synthesis of matrix metalloproteinases. In addition, MFS is accompanied by an impaired aortic contractile function and aortic endothelial-dependent relaxation, which is caused by an enhancement of the oxidative stress and increased reactive oxygen species during the progression of the disease. Many studies are currently evaluating the contribution of TGF-β-mediated biomolecular pathways to the progression of MFS aortopathy and aneurysm development, in order to discover new targets for pharmacological strategies aimed to counteract aortic dilation.

Abnormal muscle mechanosignaling triggers cardiomyopathy in mice with Marfan syndrome

Patients with Marfan syndrome (MFS), a multisystem disorder caused by mutations in the gene encoding the extracellular matrix (ECM) protein fibrillin 1, are unusually vulnerable to stress-induced cardiac dysfunction. The prevailing view is that MFS-associated cardiac dysfunction is the result of aortic and/or valvular disease. Here, we determined that dilated cardiomyopathy (DCM) in fibrillin 1-deficient mice is a primary manifestation resulting from ECM-induced abnormal mechanosignaling by cardiomyocytes. MFS mice displayed spontaneous emergence of an enlarged and dysfunctional heart, altered physical properties of myocardial tissue, and biochemical evidence of chronic mechanical stress, including increased angiotensin II type I receptor (AT1R) signaling and abated focal adhesion kinase (FAK) activity. Partial fibrillin 1 gene inactivation in cardiomyocytes was sufficient to precipitate DCM in otherwise phenotypically normal mice. Consistent with abnormal mechanosignaling, normal cardiac size and function were restored in MFS mice treated with an AT1R antagonist and in MFS mice lacking AT1R or β-arrestin 2, but not in MFS mice treated with an angiotensin-converting enzyme inhibitor or lacking angiotensinogen. Conversely, DCM associated with abnormal AT1R and FAK signaling was the sole abnormality in mice that were haploinsufficient for both fibrillin 1 and β1 integrin. Collectively, these findings implicate fibrillin 1 in the physiological adaptation of cardiac muscle to elevated workload.

Hand and fibrillin-1 deposition abnormalities in Loeys-Dietz syndrome--expanding the clinical spectrum

Loeys-Dietz syndrome (LDS) is an autosomal dominant connective tissue disorder characterized by hypertelorism, bifid uvula, cleft palate and arterial tortuosity. We report on a patient with LDS, bearing mutation in the TGFβR2 gene, whose prenatal examination demonstrated clenched fists and club feet, suggesting arthrogryposis multiplex congenita. Postnatal assessment showed digital abnormalities, including brachydactyly, camptodactyly, partial syndactyly and absent distal phalanges. With the lack of fibrillin-1 microfibril deposition as well as impaired and inadequate elastic fiber assembly in our patient's fibroblasts, we speculate that the skeletal abnormalities seen in this patient with LDS are the result of lack of these components in embryonal perichondrium and in blood vessels. We suggest that LDS should be included in the differential diagnosis of joint contractures seen pre and postnatally. Prenatal diagnosis of LDS would be important in parental counseling and early post natal diagnosis could prompt treatment before the development of detrimental vascular complications.

Usefulness of losartan on the size of the ascending aorta in an unselected cohort of children, adolescents, and young adults with Marfan syndrome

Since 2008, when angiotensin II type I receptor blockade with losartan was introduced in the prevention of cardiovascular manifestation of Marfan syndrome (MFS), a specific treatment to address the cardiovascular lesions became available. The present study aimed to compare the response of such in an unselected cohort of patients with genotyped MFS. At a tertiary university children's hospital, 20 pediatric and adolescent patients aged 1.7 to 21.6 years with genetically proven MFS were enrolled in a prospective treatment study of losartan for evaluation of the aortic dimensions and elasticity indexes. The mean follow-up period was 33 ± 11 months. A significant reduction in the normalized aortic dimensions with losartan was observed in the valve, root, sinotubular junction, and ascending aortic segments (p = 0.008, p <0.001, p = 0.012, and p = 0.001, respectively). No correlation between elasticity behavior and the decrease in the aortic dimension with losartan therapy was detectable. A significant correlation between stronger improvement and younger age at onset (r = 0.643, p = 0.002) and a longer therapy duration (r = -0.532, p = 0.016) was verifiable. However, no correlation between improvement with therapy and the type of mutation or presentation of clinical forms was remarkable. Elasticity also seemed to improve but not significantly. In conclusion, in our cohort of young patients with MFS, a significant improvement with losartan monotherapy was proved in all affected proximal aortic segments, with a better response to therapy when started at an earlier age and with a longer therapy duration.

Medical treatment for thoracic aortic aneurysm - much more work to be done

A 45 year old executive presents to your office for risk assessment after learning that his sister required an ascending aortic aneurysm repair. He is a well-informed man, concerned about his personal risk for aortic disease, and undergoes a cardiac screen which reveals a dilated ascending aortic aneurysm, measuring a maximal diameter of 4.4 cm. His aortic valve is tricuspid. He is non-Marfanoid and asymptomatic. He realizes that he does not yet meet guideline criteria for aortic surgery, but he is also cognizant of the fact that he is approaching the cut-off for surgical intervention. He wishes to minimize his future risk of aortic rupture, dissection and aortic expansion and seeks your input. Should 'medical treatment' should be employed at this stage? Is there sufficient basis to initiate any form of pharmacotherapy? Would you start a beta-adrenergic receptor blocker, an angiotensin receptor blocker, a matrix metalloproteinase inhibitor (doxycycline), or a statin to reduce his aortic risk for rupture, dissection or need for surgical repair? Does your clinical decision match evidence from existing data? Our paper will address these issues among other questions relevant to the role of medical therapy for thoracic aortic disease.

Elastic fibres in health and disease

Elastic fibres are insoluble components of the extracellular matrix of dynamic connective tissues such as skin, arteries, lungs and ligaments. They are laid down during development, and comprise a cross-linked elastin core within a template of fibrillin-based microfibrils. Their function is to endow tissues with the property of elastic recoil, and they also regulate the bioavailability of transforming growth factor β. Severe heritable elastic fibre diseases are caused by mutations in elastic fibre components; for example, mutations in elastin cause supravalvular aortic stenosis and autosomal dominant cutis laxa, mutations in fibrillin-1 cause Marfan syndrome and Weill–Marchesani syndrome, and mutations in fibulins-4 and -5 cause autosomal recessive cutis laxa. Acquired elastic fibre defects include dermal elastosis, whereas inflammatory damage to fibres contributes to pathologies such as pulmonary emphysema and vascular disease. This review outlines the latest understanding of the composition and assembly of elastic fibres, and describes elastic fibre diseases and current therapeutic approaches.

Genetic biomarkers in aortopathy

The field of aortopathy, in common with other genomic disorders, is undergoing a revolution. This is largely driven by the implementation of newer forms of genetic sequencing (massively parallel or next-generation sequencing). Advantages conferred by this technology include reduced costs, reduced sequencing time and the ability to simultaneously test multiple genes. This has a significant advantage in the identification of genes disrupted in heritable aortopathies. These advances are enabling scientists and clinicians to identify key molecular pathways; translating fundamental genetic findings into a better understanding of disease mechanisms is ultimately leading to effective treatments. In outlining contemporary knowledge of genetic biomarkers in aortopathy we seek to demonstrate that the era of genomically orientated decision-making is here.

Educational paper. Connective tissue disorders with vascular involvement: from gene to therapy

Heritable connective tissue diseases comprise a heterogeneous group of multisystemic disorders that are characterized by significant morbidity and mortality. These disorders do not merely result from defects in the amount or structure of one of the components of the extracellular matrix, as the extracellular matrix also serves other functions, including sequestration of cytokines, such as transforming growth factor beta (TGFβ). Indeed, disturbed TGFβ signaling was demonstrated in several heritable connective tissue diseases, including syndromic forms such as Marfan or Loeys-Dietz syndrome and non-syndromic presentations of thoracic aortic aneurysm/dissection. Because of these findings, new therapeutic targets have been unveiled, leading to the initiation of large clinical trials with angiotensin II type 1 receptor antagonists that also have an inhibiting effect on TGFβ signaling. Here, we present an overview of the clinical characteristics, the molecular findings, and the therapeutic strategies for the currently known syndromic and non-syndromic forms of thoracic aortic aneurysm/dissection.

Bicuspid aortic valve disease and ascending aortic aneurysms: gaps in knowledge

The bicuspid aortic valve is the most common congenital cardiac anomaly in developed nations. The abnormal bicuspid morphology of the aortic valve results in valvular dysfunction and subsequent hemodynamic derangements. However, the clinical presentation of bicuspid aortic valve disease remains quite heterogeneous with patients presenting from infancy to late adulthood with variable degrees of valvular stenosis and insufficiency and associated abnormalities including aortic coarctation, hypoplastic left heart structures, and ascending aortic dilatation. Emerging evidence suggests that the heterogeneous presentation of bicuspid aortic valve phenotypes may be a more complex matter related to congenital, genetic, and/or connective tissue abnormalities. Optimal management of patients with BAV disease and associated ascending aortic aneurysms often requires a thoughtful approach, carefully assessing various risk factors of the aortic valve and the aorta and discerning individual indications for ongoing surveillance, medical management, and operative intervention. We review current concepts of anatomic classification, pathophysiology, natural history, and clinical management of bicuspid aortic valve disease with associated ascending aortic aneurysms.

Genetic dissection of marfan syndrome and related connective tissue disorders: an update 2012

Marfan syndrome (MFS) is an autosomal dominant disorder of the connective tissue characterized by early development of thoracic aortic aneurysms/dissections together with symptoms of the ocular and skeletal systems. While most patients/families with a classic phenotypic expression of MFS harbour mutations in the gene encoding fibrillin-1 (FBN1), genetic studies of the recent years revealed that the clinical features, as well as the mutated genes, show a high degree of overlap between MFS and other connective tissue diseases (e.g. Loeys-Dietz syndrome, Ehlers-Danlos syndrome, familial thoracic aneurysms and dissections and others). We summarize herein the current knowledge about the wide spectrum of differential diagnoses and their genetic background as well as novel therapeutic approaches in order to provide appropriate counselling and clinical follow-up for the patients.

Marfan syndrome: from gene to therapy

PURPOSE OF REVIEW

Although historically Marfan syndrome (MFS) has always been considered as a condition caused by the deficiency of a structural extracellular matrix protein, fibrillin-1, the study of Marfan mouse models and Marfan-related conditions has shifted our current understanding to a pathogenic model that involves dysregulation of the cytokine-transforming growth factor beta (TGF-β) signaling.

RECENT FINDINGS

In this review, we focus on the impact of the revised MFS clinical diagnostic criteria. We discuss lessons that have been learned from molecular findings in relevant Marfan-related conditions, such as sporadic thoracic aortic aneurysm/dissection, stiff skin syndrome, acromelic dysplasias and Loeys-Dietz syndrome. We explore the latest insights into the role of the alternative TGF-β signaling pathways in MFS pathogenesis. Finally, we give an update on the current and future treatment strategies.

SUMMARY

The recent insights into the pathogenesis of MFS and related disorders have offered a prime example of translational medicine with immediate bridge between molecular findings and therapeutic options.

Surgical management of patients with Marfan syndrome: evolution throughout the years

AIM

To evaluate the evolution of surgical management in a large population of patients with Marfan syndrome.

METHODS

This is a retrospective study of patients fulfilling the Ghent criteria for Marfan syndrome, who visited the Centre de référence national pour le syndrome de Marfan et apparentés and underwent a surgical event before or during follow-up in the centre.

RESULTS

One thousand and ninety-seven patients with Marfan syndrome, according to international criteria, came to the clinic between 1996 and 2010. Aortic surgery was performed in 249 patients (22.7%; 20 children and 229 adults), including the Bentall procedure in 140 patients (56%) and valve-sparing surgery in 88 patients (35%); a supracoronary graft was performed in 19 patients (7.6%), usually for aortic dissection. During the past 20 years, the predominant reason for aortic surgery has switched from aortic dissection to aortic dilatation, while age at surgery has tended to increase (from 32.4 ± 11.9 years to 35.2 ± 12.4 years; P=0.075). Mitral valve surgery was performed in 61 patients (5.6%; six children and 55 adults), including 37 valvuloplasties (60.6%) and 18 mitral valve replacements (29.5%). No significant difference was observed when comparing mitral valve surgery before and after 2000.

CONCLUSION

Surgery performed in patients with Marfan syndrome has switched from emergency surgery for aortic dissection to elective surgery for aortic dilatation; this is associated with surgery performed at an older age despite the indication for surgery having decreased from 60mm to 50mm. No significant evolution was observed for mitral valve surgery.

Aortic Event Rate in the Marfan Population

Background—

Optimal management, including timing of surgery, remains debated in Marfan syndrome because of a lack of data on aortic risk associated with this disease.

Methods and Results—

We used our database to evaluate aortic risk associated with standardized care. Patients who fulfilled the international criteria, had not had previous aortic surgery or dissection, and came to our center at least twice were included. Aortic measurements were made with echocardiography (every 2 years); patients were given systematic β-blockade and advice about sports activities. Prophylactic aortic surgery was proposed when the maximal aortic diameter reached 50 mm. Seven hundred thirty-two patients with Marfan syndrome were followed up for a mean of 6.6 years. Five deaths and 2 dissections of the ascending aorta occurred during follow-up. Event rate (death/aortic dissection) was 0.17%/y. Risk rose with increasing aortic diameter measured within 2 years of the event: from 0.09%/y per year (95% confidence interval, 0.00–0.20) when the aortic diameter was <40 mm to 0.3% (95% confidence interval, 0.00–0.71) with diameters of 45 to 49 mm and 1.33% (95% confidence interval, 0.00–3.93) with diameters of 50 to 54 mm. The risk increased 4 times at diameters ≥50 mm. The annual risk dropped below 0.05% when the aortic diameter was <50 mm after exclusion of a neonatal patient, a woman who became pregnant against our recommendation, and a 72-year-old woman with previous myocardial infarction.

Conclusions—

Risk of sudden death or aortic dissection remains low in patients with Marfan syndrome and aortic diameter between 45 and 49 mm. Aortic diameter of 50 mm appears to be a reasonable threshold for prophylactic surgery.

Angiotensin-converting enzyme insertion/deletion polymorphism is a risk factor for thoracic aortic aneurysm in patients with bicuspid or tricuspid aortic valves

OBJECTIVE

The angiotensin-converting enzyme (ACE) is highly expressed in the aneurysmal vascular wall, in both animal models and human disease. Genetic variations in ACE could be crucial in determining the risk of thoracic aortic aneurysm (TAA). The aim of the present study was to examine the role of ACE insertion/deletion polymorphism on the risk of TAA in patients with bicuspid aortic valves or tricuspid aortic valves.

METHODS

We enrolled 216 patients (158 men; age, 58.9±14.9 years) with TAA, associated with bicuspid aortic valves (n=105) and tricuspid aortic valves (n=111) compared with 312 patients (252 men; age, 54.6±11.0 years) with angiographically proven coronary artery disease and 300 healthy controls (91 men; age, 40.4±10.5 years).

RESULTS

The genotype distribution of ACE insertion/deletion was significantly different between the patients with TAA compared with both the control group (P=.0005) and the coronary artery disease group (P=.03). The genotypes were not different between the control group and the coronary artery disease group (P=.3). Compared with the controls, both the bicuspid aortic valve patients (P=.0008) and tricuspid aortic valve patients (P<.0001) had a greater frequency of allele D. The aortic diameters were significantly different among the three genotypes (48.3±6.6, 45.3±8.9, 39.9±8.7 for the DD, DI, and II genotypes, respectively; P=.0002). A synergistic effect between the ACE D allele and hypertension was found for both an increased aortic diameter (P=.003) and the risk of TAA (P<.001). On multivariate logistic regression analysis, D allele (odds ratio, 3.0; 95% confidence interval, 1.1-8.1; P=.03) was a significant predictor of TAA.

CONCLUSIONS

ACE insertion/deletion polymorphism represents a genetic biomarker for TAA. These findings could have a significant effect on both the early detection and effective pharmacologic treatment of aortic disease.

Preventing the aortic complications of Marfan syndrome: a case-example of translational genomic medicine

The translational path from pharmacological insight to effective therapy can be a long one. We aim to describe the management of Marfan syndrome as a case-example of how pharmacological and genomic insights can contribute to improved therapy. We undertook a literature search for studies of Marfan syndrome, to identify milestones in description, understanding and therapy of the syndrome. From the studies retrieved we then weaved an evidence-based description of progress. Marfan syndrome shows considerable heterogeneity in clinical presentation. It relies on defined clinical criteria with confirmation based on FBN1 mutation testing. Surgical advances have prolonged life in Marfan syndrome. First-line prophylaxis of complications with β-adrenoceptor blockers became established on the basis that reduction of aortic pressure and heart rate would help. Over-activity of proteinases, first suggested in 1980, has since been confirmed by evidence of over-expression of matrix metalloproteinases (MMP), notably MMP-2 and MMP-9. The search for MMP inhibitors led to the evaluation of doxycycline, and both animal studies and small trials, provided early evidence that this widely used antimicrobial agent was useful. Identification of the importance of TGF-β led to evaluation of angiotensin II type I receptor (AT(1) R) blockers with highly promising results. Combination prophylactic therapy would appear rational. Pharmacological and genomic research has provided good evidence that therapy with losartan and doxycycline would prevent the aortic complications of Marfan syndrome. If on-going well designed trials confirm their efficacy, the outlook for Marfan syndrome patients would be improved considerably.

Genome wide association studies of abdominal aortic aneurysms-biological insights and potential translation applications

Abdominal aortic aneurysm (AAA) is a complex disease with important environmental risk factors and a heritability of approximately 70%. Genome wide association studies have revolutionised the study of complex disorders and offer the potential for innovative insight into disease pathogenesis and development of individualised therapeutic options. This paper reviews the progress of genome wide association studies in AAA, highlighting novel disease pathways and potential translational applications of genomic discoveries.

Extracellular matrix and heart development

The extracellular matrix (ECM) of the developing heart contains numerous molecules that form a dynamic environment that plays an active and crucial role in the regulation of cellular events. ECM molecules found in the heart include hyaluronan, fibronectin, fibrillin, proteoglycans, and collagens. Tight regulation of the spatiotemporal expression, and the proteolytic processing of ECM components by proteases including members of the ADAMTS family, is essential for normal cardiac development. Perturbation of the expression of genes involved in matrix composition and remodeling can interfere with a myriad of events involved in the formation of the four-chambered heart and result in prenatal lethality or cardiac malformations as seen in humans with congenital heart disease. In this review, we summarize what is known about the specific importance of some of the components of the ECM in relation to the cardiovascular development.

The role of the renin-angiotensin system in thoracic aortic aneurysms: clinical implications

Thoracic aortic aneurysms (TAAs) are a potential life-threatening disease with limited pharmacological treatment options. Current treatment options are aimed at lowering aortic hemodynamic stress, predominantly with β-adrenoceptor blockers. Increasing evidence supports a role for the renin-angiotensin system (RAS) in aneurysm development. RAS blockade would not only lower blood pressure, but might also target the molecular pathways involved in aneurysm formation, in particular the transforming growth factor-β and extracellular signal-regulated kinase 1/2 pathways. Indeed, the angiotensin II type 1 (AT₁) receptor blocker losartan was effective in lowering aortic root growth in mice and patients with Marfan's syndrome. RAS inhibition (currently possible at 3 levels, i.e. renin, ACE and the AT₁ receptor) is always accompanied by a rise in renin due to interference with the negative feedback loop between renin and angiotensin II. Only during AT₁ receptor blockade will this result in stimulation of the non-blocked angiotensin II type 2 (AT₂) receptor. This review summarizes the clinical aspects of TAAs, provides an overview of the current mouse models for TAAs, and focuses on the RAS as a new target for TAA treatment, discussing in particular the possibility that AT₂ receptor stimulation might be crucial in this regard. If true, this would imply that AT₁ receptor blockers (and not ACE inhibitors or renin inhibitors) should be the preferred treatment option for TAAs.