Experimental hypercholesterolemia induces ultrastructural changes in the elastic laminae of rabbit aortic valve

Impact of calcific aortic valve disease on valve mechanics

The aortic valve is a highly dynamic structure characterized by a transvalvular flow that is unsteady, pulsatile, and characterized by episodes of forward and reverse flow patterns. Calcific aortic valve disease (CAVD) resulting in compromised valve function and increased pressure overload on the ventricle potentially leading to heart failure if untreated, is the most predominant valve disease. CAVD is a multi-factorial disease involving molecular, tissue and mechanical interactions. In this review, we aim at recapitulating the biomechanical loads on the aortic valve, summarizing the current and most recent research in the field in vitro, in-silico, and in vivo, and offering a clinical perspective on current strategies adopted to mitigate or approach CAVD.

Anti-inflammatory Effects of Statins in Patients with Aortic Stenosis

Background: Aortic stenosis is an inflammatory process, as evidenced by increased tissue expression and serum levels of various endothelial cellular adhesion molecules. Aortic stenosis and atherosclerosis have many risk factors in common, including hypercholesterolemia. In atherosclerosis, statins lower cholesterol and display some anti-inflammatory activity. We hypothesized that statins might also have anti-inflammatory effects in patients with aortic stenosis.

Methods: This observational cross-sectional study measured levels of cellular adhesion molecules in 129 patients (88 male, mean age 68) with aortic stenosis (mean echo gradient 49 mm Hg, range 22 to 112) and compared levels in patients already on statin therapy for primary or secondary prevention of coronary artery disease, to those not on treatment. Concomitant conditions included hypertension (47%), diabetes (10%), and ischemic heart disease (54%). A comparison group consisted of 45 patients with stable ischemic heart disease.

Results: Patients on statins (35) were more likely to have hypertension (62% vs 42%, P = .05), but no significant differences existed in sex, age, concomitant ischemic heart disease, or diabetes. Statin-treated patients had a 20% lower vascular cellular adhesion molecule level than those without (484 ± 143 ng/L vs 604 ± 245 ng/L, P = .006). The reduction in cellular adhesion molecule levels was consistent in patients with aortic stenosis alone, aortic stenosis and ischemic heart disease, or ischemic heart disease alone. There were no differences in the levels of the other adhesion molecules between the three groups, or related to statin therapy.

Conclusion: Statin therapy is associated with reduced serum levels of vascular cellular adhesion molecules in patients with aortic stenosis. Vascular cellular adhesion molecule levels are similar in patients who have aortic stenosis, ischemic heart disease, or both. A prospective study is required to confirm this finding and to determine whether this suppression of endothelial inflammation translates into a slowing of the progression of aortic stenosis.

Animal models of organic heart valve disease

Heart valve disease is a frequently encountered pathology, related to high morbidity and mortality rates in industrialized and developing countries. Animal models are interesting to investigate the causality, but also underlying mechanisms and potential treatments of human valvular diseases. Recently, animal models of heart valve disease have been developed, which allow to investigate the pathophysiology, and to follow the progression and the potential regression of disease with therapeutics over time. The present review provides an overview of animal models of primary, organic heart valve disease: myxoid age-related, infectious, drug-induced, degenerative calcified, and mechanically induced valvular heart disease.

Animal models of calcific aortic valve disease

Calcific aortic valve disease (CAVD), once thought to be a degenerative disease, is now recognized to be an active pathobiological process, with chronic inflammation emerging as a predominant, and possibly driving, factor. However, many details of the pathobiological mechanisms of CAVD remain to be described, and new approaches to treat CAVD need to be identified. Animal models are emerging as vital tools to this end, facilitated by the advent of new models and improved understanding of the utility of existing models. In this paper, we summarize and critically appraise current small and large animal models of CAVD, discuss the utility of animal models for priority CAVD research areas, and provide recommendations for future animal model studies of CAVD.

Quantitative cardiovascular magnetic resonance for molecular imaging

Cardiovascular magnetic resonance (CMR) molecular imaging aims to identify and map the expression of important biomarkers on a cellular scale utilizing contrast agents that are specifically targeted to the biochemical signatures of disease and are capable of generating sufficient image contrast. In some cases, the contrast agents may be designed to carry a drug payload or to be sensitive to important physiological factors, such as pH, temperature or oxygenation. In this review, examples will be presented that utilize a number of different molecular imaging quantification techniques, including measuring signal changes, calculating the area of contrast enhancement, mapping relaxation time changes or direct detection of contrast agents through multi-nuclear imaging or spectroscopy. The clinical application of CMR molecular imaging could offer far reaching benefits to patient populations, including early detection of therapeutic response, localizing ruptured atherosclerotic plaques, stratifying patients based on biochemical disease markers, tissue-specific drug delivery, confirmation and quantification of end-organ drug uptake, and noninvasive monitoring of disease recurrence. Eventually, such agents may play a leading role in reducing the human burden of cardiovascular disease, by providing early diagnosis, noninvasive monitoring and effective therapy with reduced side effects.

ACE inhibition attenuates uremia-induced aortic valve thickening in a novel mouse model

Background

We examined whether impaired renal function causes thickening of the aortic valve leaflets in hyperlipidemic apoE-knockout (apoE^-/-) mice, and whether the putative effect on the aortic valves could be prevented by inhibiting the angiotensin-converting enzyme (ACE) with enalapril.

Methods

Thickening of the aortic valve leaflets in apoE^-/- mice was induced by producing mild or moderate chronic renal failure resulting from unilateral nephrectomy (1/2 NX, n = 18) or subtotal nephrectomy (5/6 NX, n = 22), respectively. Additionally, the 5/6 NX mice were randomized to no treatment (n = 8) or enalapril treatment (n = 13). The maximal thickness of each leaflet was measured from histological sections of the aortic roots.

Results

Leaflet thickness was significantly greater in the 5/6 NX mice than in the 1/2 NX mice (P = 0.030) or the unoperated mice (P = 0.003). The 5/6 NX mice treated with enalapril had significantly thinner leaflets than did the untreated 5/6 NX mice (P = 0.014).

Conclusion

Moderate uremia causes thickening of the aortic valves in apoE^-/- mice, which can be attenuated by ACE inhibition. The nephrectomized apoE^-/- mouse constitutes a new model for investigating the mechanisms of uremia-induced aortic valve disease, and also provides an opportunity to study its pharmacologic prevention.

Detection and quantification of angiogenesis in experimental valve disease with integrin-targeted nanoparticles and 19-fluorine MRI/MRS

BACKGROUND

Angiogenesis is a critical early feature of atherosclerotic plaque development and may also feature prominently in the pathogenesis of aortic valve stenosis. It has been shown that MRI can detect and quantify specific molecules of interest expressed in cardiovascular disease and cancer by measuring the unique fluorine signature of appropriately targeted perfluorocarbon (PFC) nanoparticles. In this study, we demonstrated specific binding of alphanubeta3 integrin targeted nanoparticles to neovasculature in a rabbit model of aortic valve disease. We also showed that fluorine MRI could be used to detect and quantify the development of neovasculature in the excised aortic valve leaflets.

METHODS

New Zealand White rabbits consumed a cholesterol diet for ~180 days and developed aortic valve thickening, inflammation, and angiogenesis mimicking early human aortic valve disease. Rabbits (n = 7) were treated with alphanubeta3 integrin targeted PFC nanoparticles or control untargeted PFC nanoparticles (n = 6). Competitive inhibition in vivo of nanoparticle binding (n = 4) was tested by pretreatment with targeted nonfluorinated nanoparticles followed 2 hours later by targeted PFC nanoparticles. 2 hours after treatment, aortic valves were excised and 19F MRS was performed at 11.7T. Integrated 19F spectral peaks were compared using a one-way ANOVA and Hsu's MCB (multiple comparisons with the best) post hoc t test. In 3 additional rabbits treated with alphanubeta3 integrin targeted PFC nanoparticles, 19F spectroscopy was performed on a 3.0T clinical scanner. The presence of angiogenesis was confirmed by immunohistochemistry.

RESULTS

Valves of rabbits treated with targeted PFC nanoparticles had 220% more fluorine signal than valves of rabbits treated with untargeted PFC nanoparticles (p < 0.001). Pretreatment of rabbits with targeted oil-based nonsignaling nanoparticles reduced the fluorine signal by 42% due to competitive inhibition, to a level not significantly different from control animals. Nanoparticles were successfully detected in all samples scanned at 3.0T. PECAM endothelial staining and alphanubeta3 integrin staining revealed the presence of neovasculature within the valve leaflets.

CONCLUSION

Integrin-targeted PFC nanoparticles specifically detect early angiogenesis in sclerotic aortic valves of cholesterol fed rabbits. These techniques may be useful for assessing atherosclerotic components of preclinical aortic valve disease in patients and could assist in defining efficacy of medical therapies.

Intracardiac calcification is a marker of generalized atherosclerosis

Aortic valve calcification (AVC) and carotid artery calcification (CAC) are considered to be markers of generalized atherosclerosis. However, the role of intracardiac calcification (ICC) (valvular and perivalvular calcification) is unclear. The objective of this retrospective study was to analyze the relationship between ICC and CAC, risk factors, and clinical atherosclerotic disease. Risk factors included age, sex, diabetes mellitus, hypercholesterolemia, and hypertension; clinical atherosclerosis comprised stroke, coronary artery disease, and peripheral artery disease. Between January 1, 2001, and January 1, 2004, all consecutive patients were enrolled into the study who underwent both carotid ultrasonography and transthoracic echocardiography examinations within 2 months. Patients with renal failure, substantial aortic stenosis, and carotid artery occlusion were excluded. There were 320 patients (104 men; mean +/- SEM age, 66.6 +/- 0.76 years). Positive results on carotid ultrasonography are defined as any CAC. Patients were categorized as having mild, moderate, or severe CAC. Positive results on transthoracic echocardiography were defined as any ICC; AVC was defined as mitral anulus calcification (MAC) or both. Intracardiac calcification was found in 181 patients, AVC in 51 patients, MAC in 48 patients, and calcification of both structures in 82 patients. Using multiple logistic regression analysis, ICC (odds ratio, 1.9), age (10-year periods) (odds ratio, 2.0), and the presence of peripheral artery disease (odds ratio, 1.7) were independent predictors of CAC. Carotid ultrasonography results were positive in 227 patients. For CAC, the sensitivities of AVC, MAC, both, and any ICC were 52.4%, 52.0%, 33.5%, and 71.2%, respectively, and the specificities were 84.9%, 87.1%, 92.5%, and 78.5%, respectively. The extension of ICC as 0, 1 location (AVC or MAC) , or 2 locations (AVC and MAC) was associated with the severity of CAC (P < .001, tau = 0.42). There was no difference between patients with AVC vs patients with MAC in the presence of different stages of CAC (P = .62). Intracardiac calcification (MAC or AVC) is an independent predictor of CAC as a marker of atherosclerosis, although the lack of ICC does not rule out atherosclerosis. Intracardiac calcification is related to CAC, with high specificity. The extension of ICC is related to the severity of atherosclerosis. Based on our results, antiatherothrombotic therapy should be considered in patients with ICC even before obtaining a positive carotid ultrasonography result.

Influence of receptor activator of nuclear factor kappa B on human aortic valve myofibroblasts

Calcific aortic valve stenosis, the main heart valve disease in the elderly, is based on progressive calcification and fibrous thickening of the valve. Several reports addressed the pathogenesis of tissue calcification in this disorder, but few data exist on the molecular mechanisms of the fibrosis and remodeling of the extracellular matrix. The cytokine "receptor activator of nuclear factor kappa B ligand" (RANKL), is expressed in stenotic aortic valves and involved in valvular calcification during calcific aortic valve stenosis. The present study aimed to assess the influence of RANKL on the molecular mechanisms of connective tissue remodeling. In an established cell culture model of primary human aortic valve myofibroblasts, stimulation with RANKL increased cell proliferation as compared to medium alone. Matrix metalloproteinase (MMP)-1 was detectable time-dependently in conditioned media from RANKL-stimulated cells, but absent in media from control cells. MMP-1 activity was increased by RANKL, as measured by collagenase activity assay. Zymography showed an increase in active MMP-2 in RANKL-stimulated cells. These results support the concept that MMPs are involved in the connective tissue remodeling during calcific aortic valve stenosis. RANKL might regulate this process by promoting cell proliferation and MMP expression and activation.

Experimental aortic valve stenosis in rabbits

OBJECTIVES

We studied a known rabbit model of atherosclerosis to assess the effect of a hypercholesterolemic diet on aortic valve morphology and function. We also evaluated the effects of the combination of this diet with vitamin D supplements on the development of the disease and the occurrence of valve calcification.

BACKGROUND

Aortic valve stenosis (AVS) is the most common valvular heart disease. Recent observations have suggested a link between atherosclerosis and the development of AVS. However, until now, there has been no solid direct proof of this potential link.

METHODS

Rabbits were divided in three groups: 1) no treatment; 2) cholesterol-enriched diet (0.5% cholesterol); and 3) cholesterol-enriched diet plus vitamin D(2) (50,000 IU/day). Echocardiographic assessment of the aortic valve was done at baseline and after 12 weeks of treatment. The aortic valve area (AVA) and maximal and mean transvalvular gradients were recorded and compared over time.

RESULTS

Control animals displayed no abnormalities of the aortic valve. Despite important increases in blood total cholesterol levels, animals in group 2 did not develop any significant functional aortic valve abnormality over 12 weeks. However, eight of 10 of the animals in group 3 developed a significant decrease in AVA (p = 0.004) and significant increases in transvalvular gradients (p = 0.003).

CONCLUSIONS

This study supports a potential link between atherosclerosis and the development of AVS. The differences noted between hypercholesterolemic animals with or without vitamin D(2) supplementation imply a significant role of calcium in the development of AVS, meriting further attention.

Expression of MMP2, MMP9, MT1-MMP, TIMP1, and TIMP2 mRNA in valvular lesions of the heart

Matrix metalloproteinases (MMPs) and their tissue inhibitors (TIMPs) play an important role in several diseases. This study was undertaken to investigate the mRNA synthesis of MMP2, MMP9, membrane-type 1 (MT1)-MMP, and matrix metalloproteinase inhibitors TIMP1 and TIMP2 by in situ hybridization in a set of heart mitral and aortic valves operatively removed due to degenerative or inflammatory valvular diseases. The material consisted of 21 valves, eight with endocarditis and 13 with a degenerative valvular disease. The samples were studied by in situ hybridization with specific probes for MMP2, MMP9, MT1-MMP, TIMP1, and TIMP2. Synthesis of MMP2 mRNA was found in seven valves, five with endocarditis and two with degenerative valvular disease. Signals for MMP9 mRNA were found in two cases with endocarditis and five cases with degenerative valvular disease. No signal for MT1-MMP mRNA was found in the lesions. TIMP1 mRNA, on the other hand, was found in 17 cases, both endocarditis and degenerative valvular disease. TIMP2 mRNA was found in three cases of endocarditis. The signals for MMP2, MMP9, TIMP1, and TIMP2 mRNA were localized in endothelial cells and in fibroblast-like cells expressing alpha-smooth muscle actin, thus showing myofibroblast-type differentiation. The results show that matrix metalloproteinases MMP2 and MMP9, and matrix metalloproteinase inhibitors TIMP1 and TIMP2 mRNAs are synthesized in diseased valves and suggest that they may contribute to matrix remodelling in valvular disease.