Bench to bedside defining calcific aortic valve disease: osteocardiology.

INTRODUCTION: For years, calcific aortic valve disease (CAVD) was thought to be due to a degenerative process, but recent scientific discoveries have proven it to be an active process. Understanding the cellular mechanisms for the development of disease and translating the cellular changes critical in the development of calcific phenotypes. The use of multimodality imaging has been the gold standard to define the development of calcification to determine the timing of therapy. AREAS COVERED: This review will discuss the scientific literature in a new and evolving field known as osteocardiology, which specifically defines the cellular mechanisms involved in the development of the osteogenic phenotype in the heart and vasculature. The work in this field has been highlighted by the calcific aortic valve disease working group at the NIH. This review will discuss the appropriate use criteria for multimodality imaging techniques to identify early cellular and hemodynamic disease progression in the aortic valve to help determine the timing of therapy, the osteocardiology theory. EXPERT OPINION: The authors will provide their background in basic science and clinical medicine to support the opinions in this paper.

TIEG1 is upregulated in Lrp5/6-mediated valve osteogenesis.

We have previously demonstrated that Lrp5/6/ß-catenin plays an important role in valve calcification with a specific osteogenic phenotype defined by increased bone mineral content and overall valve thickening. Recent studies indicate that TIEG1 may be involved in mediating the Wnt signaling pathway in bone, which is known to play critical roles in osteoblast differentiation and bone mineralization. Therefore, we sought to test the role of TIEG1 in mediating Wnt signaling, in an established model of hypercholesterolemic valve disease. Our previous model treated null mice with cholesterol diets: Lrp5 -/- /ApoE -/- mice versus wild-type control (n = 180). Group I (n = 60) normal diet, Group II (n = 60) 0.25% chol diet (w/w), and Group III (n = 60) 0.25% (w/w) chol diet + atorv was tested for gene expression for TIEG1, Lrp6, and Runx2. Real-time polymerase chain reaction confirmed that there is upregulation of the gene expression for TIEG1 and Runx2 in the hypercholesterolemic double knockout and single knockout valves as compared with controls with a mild increase in Lrp6. To confirm the mechanism, coexpression of ß-catenin, TIEG1, and LEF1 in valve cells in vitro, led to the coactivation of the TOPFLASH reporter, which was further confirmed by the observation that TIEG1 and ß-catenin colocalize with one another in the nucleus of valvular interstitial cells (VICs) following stimulation with transforming growth factor-ß treatment, an established activator of TIEG1. Taken together, these data implicate an important role for TIEG1 in mediating valve osteogenesis.

Osteocardiology: Defining the Go/No-Go Time Point for Therapy.

Recent epidemiological studies have revealed that the risk factors associated with coronary artery calcification (CAC), including male gender, smoking, hypertension, and elevated serum cholesterol, are similar to the risk factors associated with the development of calcific aortic valve disease (CAVD). The results of the experimental and clinical studies demonstrate that traditional risk factors initiate early atherosclerosis which over time differentiates to form bone in the heart causing clinical CAC and CAVD. Understanding the cellular mechanisms of cardiovascular calcification, the end-stage process of the atherosclerosis will help define the specific time point to modify this cellular process of bone formation in the heart termed osteocardiology. This time point between subclinical atherosclerosis and clinical calcification is the go/no-go time point, or the point of no return with severe clinical calcification in the heart. This review will summarize the development of bone formation in the heart termed osteocardiology, to define the go/no-go time point for therapy initiation to slow the progression of cardiovascular calcification.

Effect Modifications of Lipid-Lowering Therapy on Progression of Aortic Stenosis (from the Simvastatin and Ezetimibe in Aortic Stenosis [SEAS] Study).

Observational studies indicate that low-density lipoprotein (LDL) cholesterol acts as a primary contributor to an active process leading to aortic stenosis (AS) development. However, randomized clinical trials have failed to demonstrate an effect of lipid lowering on impeding AS progression. This study explored if pretreatment LDL levels and AS severity altered the efficacy of lipid-lowering therapy. The study goal was evaluated in the analysis of surviving patients with baseline data in the Simvastatin and Ezetimibe in Aortic Stenosis (SEAS) trial of 1,873 asymptomatic patients with mild-to-moderate AS. Serially measured peak aortic jet velocity was the primary effect estimate. Linear mixed model analysis adjusted by baseline peak jet velocity and pretreatment LDL levels was used to assess effect modifications of treatment. Data were available in 1,579 (84%) patients. In adjusted analyses, lower baseline peak aortic jet velocity and higher pretreatment LDL levels increased the effect of randomized treatment (p = 0.04 for interaction). As such, treatment impeded progression of AS in the highest quartile of LDL among patients with mild AS at baseline (0.06 m/s per year slower progression vs placebo in peak aortic jet velocity, 95% confidence interval 0.01 to 0.11, p = 0.03), but not in the 3 other quartiles of LDL. Conversely, among patients with moderate AS, there was no detectable effect of treatment in any of the pretreatment LDL quartiles (all p ≥0.14). In conclusion, in a non-prespecified post hoc analysis, the efficacy of lipid-lowering therapy on impeding AS progression increased with higher pretreatment LDL and lower peak aortic jet velocity (SEAS study: NCT00092677).

TIEG1 modulates ß-catenin sub-cellular localization and enhances Wnt signaling in bone.

We have previously demonstrated that TGFß Inducible Early Gene-1 (TIEG1), also known as KLF10, plays important roles in mediating skeletal development and homeostasis in mice. TIEG1 has also been identified in clinical studies as one of a handful of genes whose altered expression levels or allelic variations are associated with decreased bone mass and osteoporosis in humans. Here, we provide evidence for the first time that TIEG1 is involved in regulating the canonical Wnt signaling pathway in bone through multiple mechanisms of action. Decreased Wnt signaling in the absence of TIEG1 expression is shown to be in part due to impaired ß-catenin nuclear localization resulting from alterations in the activity of AKT and GSK-3ß. We also provide evidence that TIEG1 interacts with, and serves as a transcriptional co-activator for, Lef1 and ß-catenin. Changes in Wnt signaling in the setting of altered TIEG1 expression and/or activity may in part explain the observed osteopenic phenotype of TIEG1 KO mice as well as the known links between TIEG1 expression levels/allelic variations and patients with osteoporosis.

Fenfluramine-Phentermine is Associated with an Increase in Cellular Proliferation Ex Vivo and In Vitro.

BACKGROUND AND AIM OF THE STUDY: Fenfluraminephentermine (FenPhen) has been implicated in accelerated valvular heart disease, characterized by valvular regurgitation and thickening, and resembling the histopathologic lesions found in carcinoid. The study aim was to determine whether cellular proliferation is present in FenPhen-exposed valves, by utilizing an in-vitro model to test whether FenPhen has a direct mitogenic effect on cardiac valvular cells, as compared to serotonin. METHODS: Ex-vivo valves were tested for proliferation in surgically removed FenPhen-exposed valves (n = 10) and compared to proliferation levels in normal human cardiac valves removed at autopsy (n = 10). Immunostaining for a DNA polymerase, proliferating cell nuclear antigen (PCNA), was performed and quantified using digital imaging analysis. In-vitro assays were performed for direct proliferative effects of serotonin and FenPhen (10-6, 10-7 and 10-8 M) on porcine aortic valve subendothelial cells, using a [3H]-thymidine incorporation assay. RESULTS: Ex-vivo PCNA levels in human FenPhenexposed valves were elevated compared to controls (22.8 ± 4.54 versus 1.26 ± 0.47; p <0.001). In vivo, serotonin and FenPhen markedly increased (10-fold) cell proliferation (as measured by [3H]-thymidine incorporation) in subendothelial cells in vitro (p <0.001). This proliferative response was demonstrated by PCNA staining in carcinoid heart valves and FenPhen-exposed valves. Mechanistically, plateletderived growth factor increased cell proliferation in a dose-related manner (p <0.001), the response being inhibited by a MAP kinase inhibitor (determined by monitoring p42/44 levels). CONCLUSIONS: In vitro, FenPhen acts as a powerful mitogen on subendothelial myofibroblast valve cells. Ex vivo, cellular proliferation was significantly elevated in human FenPhen-exposed cells.

Atorvastatin Attenuates Bone Loss and Aortic Valve Atheroma in LDLR Mice.

Atherosclerosis and osteoporosis are the leading causes of mortality and morbidity. The objective of this study was to test this hypothesis in experimental hypercholesterolemia to determine whether statins play a protective role in this process. LDLR(-/-) mice (n = 60) were allocated to the following groups: group I (n = 20), normal diet; group II (n = 20), 0.25% (w/w) cholesterol diet (w/w), and group III (n = 20), 0.25% (w/w) cholesterol diet + atorvastatin for 48 weeks. Examination of aortic valves (AVA) and femurs for atherosclerosis and calcification markers included micro-CT, special stains, and calcein incorporation. The cholesterol diet induced bone formation in calcified AVA and an increase in macrophage infiltration. Hyperlipidemic bones expressed an increase in osteoclast cells and a decrease in bone formation. Atorvastatin reduced atherosclerosis and bone mineralization in AVA and increased mineralization within femur bones (p < 0.05). Atherosclerosis is present in hyperlipidemic bones and valves as characterized by macrophage and osteoclast infiltration, and it is attenuated by atorvastatin, which may have implications for therapy in the future.

SALTIRE-RAAVE: targeting calcific aortic valve disease LDL-density-radius theory.

SALTIRE and RAAVE were the first two studies to evaluate the use of statin therapy for impeding calcific aortic valve disease (CAVD). This review presents the findings of low-density lipoprotein (LDL)-density-radius theory as tested using the combined results from the SALTIRE and RAAVE studies. Patients who received statin therapy had a greater degree of LDL cholesterol lowering, seen as the % change in LDL (47 vs 2%, p = 0.012), which in itself was significantly associated with a lesser change in aortic valve area (AVA; p < 0.001 and R(2) = 0.27). The percent change in the AVA for the treated patients was 5% and 15% for the nontreated patients (p = 0.579 and R(2) = 0.03). In summary, these published findings suggest that when applying the LDL-density-radius theory, which combines the cellular biology and the hemodynamics as defined by the continuity equation for AVA, there may be a role for lipid-lowering therapy in contemporary patients with calcific aortic valve disease (CAVD).

Myxomatous mitral valve disease bench to bedside: LDL-density-pressure regulates Lrp5.

The myxomatous mitral valve is the most common form of valvular heart disease. The pathologic presentation of myxomatous mitral valve disease varies between valve thickness, degree of leaflet prolapse and the presence or absence of flail leaflets. Recent molecular biology studies have confirmed that the myxomatous changes in mitral valve prolapse equals a cartilage phenotype, which is regulated by the Lrp5 receptor. Clinically, echocardiography defines the valve pathology to determine the surgical approach to valve repair or replacement. Furthermore, the timing of surgical valve repair is controversial and is the subject of a current multicenter trial. The results will resolve the timing of whether watchful waiting versus early surgical valve repair decreases morbidity and mortality of this disease process. This review will summarize the current understanding of the cellular and hemodynamic mechanisms of myxomatous mitral valve disease, which may have future implications in the targeted therapy of this disease process.

Bicuspid aortic valve hemodynamics induces abnormal medial remodeling in the convexity of porcine ascending aortas.

The type-I bicuspid aortic valve (BAV), which differs from the normal tricuspid aortic valve (TAV) most commonly by left-right coronary cusp fusion, is frequently associated with secondary aortopathies. While BAV aortic dilation has been linked to a genetic predisposition, hemodynamics has emerged as a potential alternate etiology. However, the link between BAV hemodynamics and aortic medial degeneration has not been established. The objective of this study was to compare the regional wall shear stresses (WSS) in a TAV and BAV ascending aorta (AA) and to isolate ex vivo their respective impact on aortic wall remodeling. The WSS environments generated in the convex region of a TAV and BAV AA were predicted through fluid-structure interaction (FSI) simulations in an aorta model subjected to both valvular flows. Remodeling of porcine aortic tissue exposed to TAV and BAV AA WSS for 48 h in a cone-and-plate bioreactor was investigated via immunostaining, immunoblotting and zymography. FSI simulations revealed the existence of larger and more unidirectional WSS in the BAV than in the TAV AA convexity. Exposure of normal aortic tissue to BAV AA WSS resulted in increased MMP-2 and MMP-9 expressions and MMP-2 activity but similar fibrillin-1 content and microfibril organization relative to the TAV AA WSS treatment. This study confirms the sensitivity of aortic tissue to WSS abnormalities and demonstrates the susceptibility of BAV hemodynamic stresses to focally mediate aortic medial degradation. The results provide compelling support to the important role of hemodynamics in BAV secondary aortopathy.

Valvuloplasty with a paclitaxel-eluting balloon prevents restenosis in an experimental animal model of aortic stenosis.

BACKGROUND AND AIM OF THE STUDY: Restenosis occurs invariably within 12 months following balloon valvuloplasty (BAV) in calcific aortic valve disease (CAVD), and is a limiting factor of this treatment. Cellular proliferation secondary to balloon injury is thought to play a pivotal role in the mechanism of restenosis. The study aim was to investigate the potential role of a paclitaxel-eluting valvuloplasty balloon to mitigate the progression of restenosis in an animal model of CAVD. METHODS: Fifty-three rabbits were fed with an aortic stenosis (AS)-inducing diet (cholesterol 0.5% plus vitamin D3 50,000 IU/day) for three months. The surviving animals (n = 40) underwent echocardiographic and invasive assessments, followed by valvuloplasty, randomly using either a paclitaxel-coated (3 µg/mm2) or a plain balloon. At one month after BAV, the surviving animals (n = 28) underwent repeat assessments, followed by histology and micro-computed tomography (MicroCT) analysis of the aortic valve. RESULTS: The baseline and post-BAV transvalvular gradients, aortic valve area (AVA), left ventricular stroke work loss (SWL) and aortic valve resistance (AVR) were similar between the groups (14 rabbits were assigned to paclitaxel-eluting, and 14 to plain balloon). Significant differences between the groups were observed at one-month post-BAV, which was suggestive of diminished restenosis in the paclitaxel-balloon group (mean maximum transvalvular pressure gradient 7.7 ± 7.7 versus 3.6 ± 3.7 mmHg, p = 0.08; AVA 0.91 ± 0.59 versus 0.55 ± 0.22 cm2, p = 0.04; SWL 3.5 ± 4.0 versus 8.6 ± 8.0%, p = 0.047; AVR 86 ± 71 versus 177 ± 137 dynes/s/cm(-5), p = 0.039). Histology demonstrated decreased leaflet thickness (0.60 ± 0.15 versus 0.71 ± 0.17 mm, p = 0.03), proliferating cell nuclear antigen (PCNA) staining (grade 1.53 ± 0.04 versus 2.24 ± 0.55, p = 0.049), and calcification in the paclitaxel-balloon group. CONCLUSION: Use of a paclitaxel-eluting valvuloplasty balloon in an animal model of AS resulted in attenuated restenosis, secondary to decrease in valve proliferation and calcification.

Defining the role of fluid shear stress in the expression of early signaling markers for calcific aortic valve disease.

Calcific aortic valve disease (CAVD) is an active process presumably triggered by interplays between cardiovascular risk factors, molecular signaling networks and hemodynamic cues. While earlier studies demonstrated that alterations in fluid shear stress (FSS) on the fibrosa could trigger inflammation, the mechanisms of CAVD pathogenesis secondary to side-specific FSS abnormalities are poorly understood. This knowledge could be critical to the elucidation of key CAVD risk factors such as congenital valve defects, aging and hypertension, which are known to generate FSS disturbances. The objective of this study was to characterize ex vivo the contribution of isolated and combined abnormalities in FSS magnitude and frequency to early valvular pathogenesis. The ventricularis and fibrosa of porcine aortic valve leaflets were exposed simultaneously to different combinations of sub-physiologic/physiologic/supra-physiologic levels of FSS magnitude and frequency for 24, 48 and 72 hours in a double cone-and-plate device. Endothelial activation and paracrine signaling were investigated by measuring cell-adhesion molecule (ICAM-1, VCAM-1) and cytokine (BMP-4, TGF-ß1) expressions, respectively. Extracellular matrix (ECM) degradation was characterized by measuring the expression and activity of the proteases MMP-2, MMP-9, cathepsin L and cathepsin S. The effect of the FSS treatment yielding the most significant pathological response was examined over a 72-hour period to characterize the time-dependence of FSS mechano-transduction. While cytokine expression was stimulated under elevated FSS magnitude at normal frequency, ECM degradation was stimulated under both elevated FSS magnitude at normal frequency and physiologic FSS magnitude at abnormal frequency. In contrast, combined FSS magnitude and frequency abnormalities essentially maintained valvular homeostasis. The pathological response under supra-physiologic FSS magnitude peaked at 48 hours but was then maintained until the 72-hour time point. This study confirms the sensitivity of valve leaflets to both FSS magnitude and frequency and suggests the ability of supra-physiologic FSS levels or abnormal FSS frequencies to initiate CAVD mechanisms.