Statins for Calcific Aortic Valve
Stenosis: Into Oblivion After
SALTIRE and SEAS? An Extensive
Review from Bench to Bedside
Hadewich Hermans, MD, Paul Herijgers, MD, PhD,
Paul Holvoet, PhD, Eric Verbeken, MD, PhD,
Bart Meuris, MD, PhD, Willem Flameng, MD, PhD,
and Marie-Christine Herregods, MD, PhD
Abstract: Calcific aortic stenosis is the most frequent heart
valve disease and the main indication for valve replacement
in western countries. For centuries attributed to a passive
wear and tear process, it is now recognized that aortic
stenosis is an active inflammatory and potentially modifiable
pathology, with similarities to atherosclerosis. Statins were
first-line candidates for slowing down progression of the
disease, as established drugs in primary and secondary
cardiovascular prevention. Despite promising animal experiments and nonrandomized human trials, the prospective
randomized trials SEAS and SALTIRE did not confirm the
expected benefit. We review SEAS and SALTIRE starting
with the preceding studies and discuss basic science experiments covering the major known contributors to the pathophysiology of calcific aortic valve disease, to conclude with a
hypothesis on the absent effect of statins, and suggestions
for further research paths. (Curr Probl Cardiol 2010;
35:284-306.)
alcific aortic valve disease is a common and progressive pathology. The prevalence of sclerosis is reported to be ⬎25% in the
population aged ⬎65 years; the prevalence of severe aortic valve
stenosis is reported to be ⬎2.5% in the population aged ⬎75 years and
C
The authors have no conflicts of interests to disclose.
Hadewich Hermans, MD, is supported by the Flanders Research Foundation (FWO) to prepare a PhD thesis.
Curr Probl Cardiol 2010;35:284-306.
0146-2806/$ – see front matter
doi:10.1016/j.cpcardiol.2010.02.002
284
Curr Probl Cardiol, June 2010
⬎8% in the population aged ⬎85 years.1 Aortic valve stenosis (AS) is the
primary indication for valve replacement in western countries, and the
number will only increase as elderly people are a growing subpopulation.
At present the only established therapy for AS is valve replacement.2
Medical prevention of progression is a subject of substantial research for
a decade as it was recognized that aortic valve disease is not only a
passive wear and tear process but an active inflammatory process with
histopathologic changes and risk profile similar to atherosclerosis, occurring from the age of 35 years. This generated possible targets for therapy.
Statins were first-line candidates as commercially available drugs with
established benefit in primary and secondary cardiovascular prevention
by atherosclerosis stabilization. Retrospective studies3-7 and prospective
nonrandomized studies8,9 have shown that statins significantly slowed
down progression. SEAS10 and SALTIRE,11 being the only prospective
randomized trials published to date, did not confirm the effect of statins
on rate of progression. How come?
What Preceded SALTIRE and SEAS?
Epidemiology and Histopathology: (Dis)Similarities
Between Calcific Aortic Valve Disease and
Atherosclerosis
Since the Helsinki Aging Study12 and Cardiovascular Health Study,13 it
is recognized that calcific aortic valve disease and atherosclerosis show an
overlap in clinical risk factors, ie, age, male gender, hypertension,
smoking, dyslipidemia, renal dysfunction, and diabetes. However, there is
no absolute correlation as only 33% of the patients in the Euro Heart
Survey underwent concomitant coronary artery bypass grafting (CABG)
at aortic valve replacement (AVR).14 Histopathologic comparison revealed that both entities are characterized by accumulation of (oxidized)
low-density lipoprotein (oxLDL), inflammation, calcification, and bone
formation.15-17 We have to emphasize that there are also differences:
calcification occurs much earlier in AS, the most prominent cell type is
not the smooth muscle cell but the “fibroblast,” and plaque instability as
the cause of symptoms is not a main issue in contrast to atherosclerosis.
Animal Experiments: Based on a Dyslipidemic Model
To date, the only animal experiment showing benefit of statins is AS,
concerns a hypercholesterolemic rabbit model.18 As such, this might only
be translated to patients with dyslipidemia as the facilitating factor. The
quest for drug therapy is hampered by the lack of a low-cost spontaneous
Curr Probl Cardiol, June 2010
285
animal model. Only aging swine develop valvular sclerosis without an
inciting factor,19 while the other species require diets or genetic mutations. The rabbit models are based on high-cholesterol diets with or
without vitamin D supplementation.18,20-25 The mouse models are either
dyslipidemic like the rabbit models, by diets or by mutations in the lipid
metabolism (apolipoprotein, LDL receptor, apolipoproteinB), or are based on
mutations in players of calcification and bone formation (endothelial nitric
oxide synthase (eNOS), matrix gla protein, and Notch1 or Madh6) and as
such they might not mirror the development and progression of the disease
in humans where AS develops at later age by a complex inflammatory
process.26-33
Nalini M. Rajamannan: In 2009, the current use of hyperlipidemic animal
models, whether genetic or diet-induced, provides a foundation for evolving
studies in the field of calcific aortic valve disease. The authors are correct that
the published animal models do not recapitulate fully human calcific aortic
valve disease. Each published model, to date, has provided unique cellular
features that recapitulate the published discoveries important in the phenotype of calcification in the aortic valve. The eNOS null mouse by Lee TC, et
al,28 expresses bicuspid aortic valves in only 27% of the mouse colonies and
not spontaneous calcification. The genetic mouse model that has demonstrated severe aortic stenosis in a third of the mice over a 2-year period is the
Reversa mouse published by Weiss RM, et al.32 This mouse model is the first
to develop severe stenosis in a third of the mouse cohorts studied.
Retrospective Observational Studies: Patients on Statins
for Established Indication
Early 2000 retrospective observational studies were reported (Table 1).3-7
Note that consequently all patients received statins in primary or secondary prevention, and note that in the stage of aortic valve disease, none
included sclerosis. Aronow focused on aortic valve calcification; the other
groups focused on hemodynamic severity. All investigators found a
significant benefit of statins on the parameters regardless of the degree of
AS. As such, the authors concluded that statins might be beneficial in
advanced stages of the evolutionary disease, considered the retrospective
and nonrandomized nature of the studies. The impact of cholesterol level
on hemodynamic progression was controversial: Aronow and Novaro
described an association between cholesterol level and progression; in the
trials of Bellamy and Rosenhek they were unrelated.
Nalini M. Rajamannan: There is a recent publication by Antonini-Canterin F,
et al,98 demonstrating that there is a stage-related effect of statin treatment
286
Curr Probl Cardiol, June 2010
TABLE 1. Retrospective and prospective nonrandomized trials
Investigators
(y)
Retrospective
Aronow
(2001)
Novaro
(2001)
Bellamy
(2002)
Shavelle
(2002)
Rosenhek
(2004)
Prospective
RAAVE
(2007)
n (n on
statins)
Follow-up
Grade, AS at
baseline
Endpoint
Pro statins
180 (62) 2.75 ⫾ 1 y
Mild
⌬Pmax
Yes (P ⬍ 0.01)
174 (57) 1.75 ⫾ 0.6 y
Mild to moderate
Yes (P ⫽ 0.03)
156 (38)
3.7 ⫾ 2.3 y
Mild to moderate
⌬Pmax,
AVA
AVA, Vmax
65 (28)
2.5 ⫾ 1.6 y
211 (82)
2.0 ⫾ 1.5 y
No hemodynamic AVC
evaluation
Mild to severe
AVA, Vmax
121 (61)
1.4 ⫾ 0.46 y Moderate to
severe
Vmax
Yes (P ⫽ 0.04)
Yes (P ⫽ 0.006)
Yes (P ⬍ 0.0001)
Yes (P ⫽ 0.007)
Abbreviations: y, year; n, number of patients; ⌬Pmax, peak transaortic gradient; AVA, aortic
valve area; Vmax, peak transaortic velocity; AVC, aortic valve calcium; RAAVE, Rosuvastatin
affecting aortic valve endothelium to slow the progression of aortic valve stenosis.
on the progression of aortic valve sclerosis and stenosis. This study also
demonstrates the importance of treating the earlier stages of this disease
with a notable difference in treatment effect.
Prospective Nonrandomized Studies: Patients on Statins
for Established Indication
Moura et al performed the Rosuvastatin Affecting Aortic Valve endothelium to slow the progression of aortic stenosis study (RAAVE).8
Although this study was prospective, it was nonrandomized comprising
only 121 patients with moderate to severe AS; 61 of them were on statins
in accordance to current guidelines. Statins significantly slowed down
hemodynamic progression, but here again the observed effect of statins
cannot be broadened to AS patients without dyslipidemia as facilitating
factor. Pohle et al performed electron beam tomography on 104 patients
at baseline and after a mean interval of 15 months.9 Patients were divided
in 2 groups according to LDL cholesterol level: 57 patients ⬍130 mg/dL,
of which 39 were on statin treatment; and 47 patients ⬎130 mg/dL, of
which 15 were on statin treatment. All patients had progression of aortic
valve calcification score, but progression was significantly less in the
group ⬍130 mg/dL. Multiple regression analysis showed that LDL level
was an independent predictor of progression, while age, smoking,
Curr Probl Cardiol, June 2010
287
hypertension, and diabetes were not. Statin use was not entered in the
regression model, but the authors describe that the patients on statin
treatment with LDL ⬍130 mg/dL had a significantly slower progression
than patients on insufficient dose to control plasma LDL and concluded
that adequate lipid-lowering decreases progression of AS.
Nalini M. Rajamannan: The RAAVE study was designed to treat patients
with elevated LDL and calcific aortic valve disease compared with patients
with normal LDL and calcific aortic valve disease, because of the ethical
issues related to randomizing patients with elevated LDL to no statin after the
series of published papers demonstrating the clinical benefits of lipid lowering, for example, the 4-S trial. Lancet 344(8934):1383-9, 1994.
Pleiotropic Effects of Statin: Pathways Partly Unknown
The discrepancies regarding the association between cholesterol level
and hemodynamic progression of AS give rise to the question of the
mechanisms by which statins slow down progression in patients with
dyslipidemia: only by lipid lowering or in combination with pleiotropic
effects. In atherosclerosis the importance of the pleiotropic effects of
statins on cardiovascular mortality and morbidity is well established; the
pathways and their relative contribution however are partly unknown.
Statins are reported to cause an improvement of endothelial dysfunction,
to have anti-inflammatory and antioxidant effects, and to be capable of
plaque stabilization, as is nicely reviewed by Davignon.34 The improvement of endothelial dysfunction is shown to be caused by increased NO
production: at first by diminished inhibition of eNOS-activity by lowering
of LDL, as LDL is able to increase caveolin-1, an inhibitor of eNOS;
second, by enhancement of constitutive eNOS activity by (1) stabilization
of eNOS messenger RNA, (2) activation of Akt (protein kinase B) in
endothelial cells and as such phosphorylation of its substrate eNOS, and
(3) prevention of translocation to the cell membrane of Rho GTPase with
consequently less negative regulation of eNOS. The antioxidant effect of
statins with less production of the cytotoxic oxLDL might be due to direct
diminution of the oxidative ability of macrophages, and to free radical
scavenging. On top statins might decrease the activity of macrophage
CD36, a receptor of oxLDL and as such foam cell formation. With
regards to the anti-inflammatory effect, statins are reported to cause a
reduction of plasma C-reactive protein and reduction of adhesion molecules, the latter however with conflicting results. Plaque stabilization is
described as the net effect of the mechanisms discussed above, caused by
288
Curr Probl Cardiol, June 2010
a smaller lipid core, less macrophages and T-lymphocytes, less apoptosis,
and more collagen content with less matrix metalloproteinase-2 (MMP-2),
and enhanced tissue inhibitor of matrix metalloproteinase-1 (TIMP-1) immunoreactivity. As conviction grew that AS has a genesis and evolution
similar to atherosclerosis, the next step was the hypothesis that statins might
be able to influence the progression. There was preliminary proof of concept
by the mentioned retrospective and prospective nonrandomized trials that
paved the way for the setup of prospective randomized trials.
Nalini M. Rajamannan: The experimental studies in the field of vascular
disease and statins have been clearly defined. The pleiotropic effects of
statins in the signaling pathways include eNOS, hsCRP, MMP-2, and TIMP-1.
There is a growing body of literature in the field of aortic valve disease in vitro
and in vivo demonstrating that statins have specific pleiotropic effects in the
valve also, including the following: eNOS, Rajamannan et al. Atorvastatin
inhibits calcification and enhances nitric oxide synthase production in the
hypercholesterolemic aortic valve. Heart 91(6):806-10, 2005; extracellular
nucleotides, Osman et al. A novel role of extracellular nucleotides in valve
calcification: a potential target for atorvastatin. Circulation 114(1)(Suppl):
I566-72, 2006; and inhibition of bone matrix synthesis, Wu B, et al.56
SALTIRE and SEAS
Study Aim
The investigators hypothesized that statins ⫾ ezetimibe slow down progression of AS. SALTIRE had as primary endpoint progression in aortic jet
velocity and computed tomography aortic valve calcium score, and as
secondary endpoints, AVR, death from any cause, hospitalization for any
cause, hospitalization for cardiovascular causes, and a composite of clinical
endpoints (death from cardiovascular causes, AVR, hospitalization attributable to severe AS). The primary endpoint of SEAS was the composite of
cardiovascular death, AVR, nonfatal myocardial infarction, congestive heart
failure because of progression of AS, CABG, percutaneous coronary
intervention, hospitalized unstable angina, and nonhemorrhagic stroke.
The secondary endpoints were aortic valve events (AVR, congestive heart
failure because of progression of AS, and cardiovascular death), echocardiographic progression, and ischemic events (CABG, percutaneous
coronary intervention, stroke, unstable angina, nonfatal myocardial infarction, death from cardiovascular cause). The rationale for the composite primary endpoint was the assessment of aggressive lipid-lowering on
the entire cardiovascular burden in AS patients (Table 2).
Curr Probl Cardiol, June 2010
289
TABLE 2. Published prospective randomized trials
n (n on statins ⫾ ezetimibe)
Follow-up
Grade, AS at baseline
Primary endpoints
Secondary endpoints
Pro statins
SALTIRE (2005)
SEAS (2008)
155 (77)
2.08 y
Mild to severe
Vmax (P ⫽ 0.95)
AVC (P ⫽ 0.80)
Composite (P ⫽ 0.19)
Death from cardiovascular
causes (P ⫽ 1.0)
Aortic valve replacement
(P ⫽ 0.17)
Hospitalization for severe
AS (P ⫽ 0.73)
Death from any cause
(P ⫽ 0.73)
Hospitalization for any
cause (P ⫽ 0.84)
No
1873 (944)
4.35 y
Mild to moderate
Composite (P ⫽ 0.59)
AVA, Vmax (P ⫽ 0.83)
Aortic valve events
(P ⫽ 0.73)
Ischemic events
(P ⫽ 0.02)
No
Abbreviations: n, number of patients; Vmax, peak transaortic velocity; AVC, aortic valve calcium;
AVA, aortic valve area; SALTIRE, Scottish Aortic Stenosis and Lipid Lowering Trial, Impact on
Regression; SEAS, Simvastatin and Ezetimibe In Aortic Stenosis Study.
Study Design and Baseline Characteristics
The trials were double-blind, randomized, and placebo-controlled, and
SEAS was multicenter. The inclusion criterion was asymptomatic calcific
AS, in SALTIRE with a peak jet velocity of at least 2.5 m/s, in SEAS
between 2.5 and 4 m/s. Both had similar exclusion criteria namely age
⬍18 y, contraindications for or current therapy with statins, guidelines
indication for statins, left ventricular dysfunction, significant valvular
disease other than AS, uncontrolled hypertension, or renal insufficiency.
As such, the study population of the 2 trials does not fully resemble the
general AS population as the study cohorts had limited clinical risk
factors for AS progression. All patients underwent echocardiography ⫾
computed tomography at baseline, annually during follow-up, and at
study termination, while adverse effects and lipid profile were monitored
more frequently.
Results
SALTIRE did not show a significant reduction in AS progression rate,
nor in clinical endpoints. SEAS showed similar results, with the exception
of a significant effect on ischemic events, dominated by a reduction of the
need for CABG in the simvastatin-ezetimibe group. SEAS did not have a
treatment group on simvastatin or ezetimibe alone. Long-term outcome
290
Curr Probl Cardiol, June 2010
trials of ezetimibe, acting on the intestinal sterol transporter, are not
published yet. As such, the relative contribution of both drugs on this
endpoint cannot be determined.
Nalini M. Rajamannan: The SEAS and SALTIRE investigators are pioneers in
the field of valvular heart disease trials. These studies provide valuable
information for the future design of valvular heart disease trials. The design of
these trials came out before the series of publications for the hyperlipidemic
animal models, which have contributed to the future design of clinical valve
trials.
Back to Basics: Pathophysiology of Aortic
Valve Stenosis
The normal aortic valve leaflets are covered with endothelium, are
avascular, and consist of the 3 following layers: the ventricularis at the
ventricular side; the spongiosa; and the fibrosa at the aortic side of the leaflet.
The ventricularis is composed of closely aligned elastin fibers; the spongiosa
consists of loose connective tissue, and the fibrosa contains collagen
fibers. The layers are populated by mesenchymal cells namely valve
interstitial cells (VICs), maintaining leaflet integrity. The early lesion is
characterized by subendothelial plaque-like lesions at the aortic side, with
progressive infiltration of the adjacent fibrosa, and consists of accumulation of lipoproteins, inflammatory cells, and microcalcifications.15-17 As
the lesion progresses, neo-angiogenesis is noted,35 a process of enhanced
calcification, and active bone formation.36 While the AS lesion is
characterized at the microscopic level, the molecular pathways remain
challenging to unravel. We discuss the most studied pathways in the
(patho)physiology as presented in Fig 1.
Mechanical Stress and Shear Stress
Although calcific AS is now recognized as an active process with
similarities to atherosclerosis, instead of an unmodifiable pathology, due
to long-term mechanical stress and leading to passive accumulation of
calcium, caution is warranted to forget the contribution of increased
mechanical and decreased or turbulent shear stress to the initiation and
progression of AS. Patients with bicuspid valves present 2 decades earlier
than patients with tricuspid valves.37 Hypertension is a risk factor for
AS,12,13 and lesions are noted to initiate at the flexion area of the leaflets
where stress is highest.38 All emphasizing the role of mechanical stress
currently believed to be leading to endothelial disruption. The noncoroCurr Probl Cardiol, June 2010
291
FIG 1. Pathophysiology of calcific aortic valve stenosis. Abbreviations: NO, nitric oxidep;
ICAM, intercellular adhesion molecule; VCAM, vascular cell adhesion molecule; TGF␤,
transforming growth factor ␤; ACE, angiotensin converting enzyme; oxLDL, oxidized LDL;
TNF-␣, tumor necrosis factor ␣; A1R, angiotensin receptor 1; B2R, bradykinin receptor 2; Lrp
5, low-density lipoprotein receptor-related protein 5; RANK, receptor activator of nuclear factor
kappa (B); RANKL, RANK ligand; NF-␬B, nuclear factor kappa (B); cbfa-1, core binding factor
alpha-1; Msx-2, msh homeobox 2; qVIC, quiescent valvular interstitial cell; obVIC, osteoblastic
valvular interstitial cell; aVIC, activated valvular interstitial cell; EGF, vascular endothelial
growth factor; MMPs, matrix metalloproteinases; AS, aortic stenosis. (Color version of figure is
available online.)
nary cusp is often the first affected, probably by more pronounced
endothelial dysfunction as this cusp might encounter less shear stress than
the coronary cusps due to absence of diastolic coronary flow. The fibrosa
is affected first as the aortic side of the valve is exposed to turbulent flow,
while the ventricularis is exposed to laminar flow.39 The molecular
pathways from stress to endothelial dysfunction are subjected to substantial research in the atherosclerosis field, with NO as a key player.40 As
soon as subendothelial lesions are present, endothelial dysfunction is
maintained by oxLDL and inflammatory cells.41 The endothelium covering the valve leaflets, however, is distinct from vascular endothelium.
We comment on this below.
Regarding the role of mechanical and shear stress, we now leave the
ground paths. Quoting Robicsek et al and Singh et al, the importance of
292
Curr Probl Cardiol, June 2010
the functional assembly of the valve leaflets, corresponding sinuses, and
sinotubular junction is often overlooked.42,43 Intact sinuses and sinotubular junction create optimal distribution of pressure load and proper
valve opening and closure, while loss of aortic wall compliance leads to
significant stress overload of the leaflets. Loss of vascular compliance
occurs in every aging subject due to gradual loss of elastin fibers in the
media and is more pronounced in patients with hypertension, diabetes,
and renal failure, the latter due to superposition of media calcification. As
such, the role of mechanical stress is not restricted to the initiating step,
but instead is continuous and progressive. Once sclerosis is initiated in the
leaflets, the thickened and stiffened leaflets themselves also promote
unfavorable stress distribution. This self-perpetuating process might
partly cause the failure of statins to slow down AS progression when
administrated at later stages.
Recent reports on the molecular bridge between mechanical stress and
AS describe in vitro testing of intact porcine valves or aortic VICs. To
interpret the results of in vitro experiments, remember that the aortic valve
is exposed to a composite of hemodynamic forces: during systole pulsatile
pressure and shear stress (laminar at the ventricularis, turbulent at the fibrosa),
and during diastole cyclic stretch and turbulent shear stress, transmitted to the
VICs by endothelial cells and matrix.44 Cell proliferation, apoptosis,
collagen content, cathepsin S and K expression, MMP-1, -2, and -9
expression and activity increase with increased cyclic stretch, while
cathepsin L expression, TIMP-1 expression, and activity are reduced.45
Transforming growth factor ␤1 (TGF␤1) acts synergistically with cyclic
stress46 and is also a key player in upregulation of vascular cell adhesion
molecule-1 and intercellular adhesion molecule 1 in the valvular endothelium at the aortic side in response to oscillatory shear stress.47 The
endothelium is also capable of regulating the mechanical properties of the
aortic valve cusps. Endothelin-1 leads to increase in cusp stiffness, while
serotonin has the opposite effect; both are endothelium-dependent effects
exerted on the VICs.48 The role of the valvular endothelium in vivo in
stress distribution, and how mechanotransduction to the VICs takes place,
requires further research.
Valvular Endothelium
The endothelium is not a uniform organ, similarly functioning in the
entire cardiovascular bed. Butcher et al highlighted that the valvular
endothelium is distinct from the vascular endothelium. They showed that
in response to shear stress valvular endothelial cells respond by aligning
perpendicular and vascular endothelial cells parallel to the direction of the
Curr Probl Cardiol, June 2010
293
flow, with differences in focal adhesion arrangement and signal kinases.49
Subsequently they showed transcriptional differences between porcine
aortic valve and aortic endothelial cells exposed to laminar shear stress:
valvular endothelial cells are less intrinsically inflammatory, although
similar antioxidant and anti-inflammatory genes are expressed and express more genes associated with chondrogenesis and less with osteogenesis. In both cell types shear stress protected against calcification by
downregulation of bone morphogenic protein 4, in valvular cells also by
inhibition of cadherin-11 and in aortic cells by inhibition of periostin.50
As such, the effect of statins on endothelial dysfunction as described for
vascular endothelium might not be as pronounced for valvular endothelium.
Nalini M. Rajamannan: The gene expression of valve endothelium has been
described by Simmons CA, et al,19 demonstrates the unique genotype of the
valve aortic endothelial surface versus the ventricular surface the geographic
differences that may contribute to the difference in the predisposition of the
valve to calcify on the aortic surface.
Aortic Valve Interstitial Cells
As discussed by Liu et al, the terms valvular fibroblasts and osteoblasts
should be replaced by the at present known 5 phenotypes of valvular
interstitial cells: either embryonic progenitor, quiescent (qVICs), activated (aVICs), progenitor (pVICs), or osteoblastic (ob)VICs.51 VICs are
distinct mesenchymal cells that adapt to the valvular environment with a
change in phenotype with specific detectable markers. Embryonic progenitor endothelial/mesenchymal cells, present in the embryonic cardiac
cushions, give rise to qVICs by the developmental process of endothelialto-mesenchymal transformation (EMT). Their role seems however not
finished after the developmental period, as plasticity of aortic and
pulmonary valve endothelium was described, which might lead to the
hypothesis that EMT takes place again in adult valves in response to
injury, giving rise to pVICs.52,53 Quiescent VICs maintain physiologic
valve structure and inhibit angiogenesis in the leaflets. They can give rise
to activated and obVICs in response to a number of chemokines and
growth factors, one of the most important being TGF␤ from activated
endothelium. Activated VICs contain ␣-smooth-muscle actin and respond
to valve injury and mechanical forces by repair processes including
proliferation, migration, and matrix remodeling. ObVICs participate in
calcification, osteogenesis, and chondrogenesis and secrete alkaline phos294
Curr Probl Cardiol, June 2010
phatase, osteocalcin, osteopontin, and bone sialoprotein. The least defined
phenotype is the pVIC that might originate from the heart valve, the bone
marrow via the circulation, or the endothelium via EMT and is CD-34-,
CD-133-, and/or S100-positive. In case of in vitro experiments, next to
the VIC phenotype used, also the culture conditions should meticulously
be described as the passage number; cell density and matrix all affect the
phenotype via incompletely known pathways. Recent intriguing papers
describe that VIC-differentiation and -calcification is regulated by extracellular matrix stiffness, as is the efficacy of statin treatment. Yip et al
describe that on compliant calcifying matrices VICs transform to an
osteoblast phenotype and form calcification noduli by active deposition.
On a stiff matrix, however, they transform to an ␣-smooth-muscle
actin-expressing phenotype with apoptosis-dependent dystrophic calcification. On the stiff matrix, calcification was strongly enhanced by
TGF␤1, but not on compliant matrices, where the VICs expressed less
TGF␤ receptor I.54 This is important, as in current opinion, “myofibroblasts” are transforming to “osteoblasts” in the evolution of AS, while this
study implicates that the main cell type might be the “osteoblast” or
obVIC in the early stage and the “myofibroblast” or aVIC in the later
stage. Monzack et al reported that the inhibiting and even dissipating
effect of simvastatin on calcific nodule formation was dose-dependent,
matrix-dependent, and time-dependent.55 In most VIC studies cells are
cultured on unmodified tissue culture polystyrene (TCPS), but they
cultured the cells also on TCPS coated with either laminin or fibrin and
found that the effect of simvastatin was more pronounced in laminin
TCPS. Their time experiments showed that the effect of simvastatin was
only significant when applied within 1 hour after application of TGF␤.
Adding to the importance of time dependency of statin admission, Wu et
al described that simvastatin inhibited dystrophic calcification by valve
“myofibroblasts,” but promoted calcific nodule formation by “osteoblasts,”56 analogous to the “statin paradox” described in osteoporosis
research. Anger et al showed that statin therapy enhanced phosphorylated
ERK in end-stage AS, which might enhance proliferative degeneration.57
These experiments underscore the absolute necessity of studying the
complete in vivo evolution of the disease, with attention for macromechanics, cells and cell types, matrix composition, and matrix micromechanics to understand the pathophysiology, and investigate drug effects,
including timing of administration. With the advent of molecular imaging
as described by Aikawa et al, this could be in the near future for animal
models, but not yet for patients.33
Curr Probl Cardiol, June 2010
295
Nalini M. Rajamannan: Aortic valve myofibroblast cell is a mesenchymalderived cell that has the ability to differentiate to different valve phenotypes
including a robust osteogenic phenotype. Chen JH, et al. Identification and
characterization of aortic valve mesenchymal progenitor cells with robust
osteogenic calcification potential. Am J Pathol 174(3):1109-19, 2009.
Extracellular Matrix
To date, little is known about the evolution of extracellular matrix,
although primordial to understand both cell-cell- and cell-matrix communication. Comparison of degenerative aortic valves obtained at replacement surgery and normal valves at heart transplantation learned that the
diseased valves have an extensive matrix remodeling process, with as a
result disrupted basal membranes, more collagen than elastin, and
opportunity for invasion of inflammatory cells and neoangiogenesis. The
MMPs and cathepsins are the most studied. An increase of MMP-1, -3,
and -9 have consistently been reported, while the effect on their inhibitors
TIMP-1 and -2 have shown conflicting results.58-60 Cathepsin S, K, V,
and G are significantly increased in stenotic aortic valves, with cathepsin
G being highly expressed in activated mast cells.61,62 The importance of
inflammation is underscored by colocalization of TGF␤1 and cathepsin G
in mast cells, and of tumor necrosis factor-␣ with MMP-1.62,63 Remember that both inflammation and mechanical stress are reported to be able
to upregulate matrix remodeling and can act synergistically as described
above.
Nalini M. Rajamannan: Grande-Allen KJ, et al. Glycosaminoglycan synthesis
and structure as targets for the prevention of calcific aortic valve disease.
Cardiovasc Res 2007;76(1):19-28, have demonstrated that extracellular matrix synthesis is an important disease phenotype and target for therapeutic
interventions.
Lipoproteins
In the 1990s the uptake of serum neutral lipids and apolipoproteins, and
lipid oxidation around calcium deposits and leukocytes were described in
AS, resembling the atherosclerotic process.16,17 Mohty et al recently
conducted an important study on severely stenotic valves, explanted at
AVR,64 supporting the hypothesis that oxLDL also in AS participates in
recruitment and activation of macrophages, as oxLDL colocated with
macrophages, and an increased oxLDL score correlated with higher tumor
296
Curr Probl Cardiol, June 2010
necrosis factor-␣ expression. An increase in oxLDL score also correlated
with increased tissue remodeling score, as defined by Warren and Yong,65
supporting the contribution of oxLDL to calcification in AS, while plasma
small LDL correlated with disease progression and oxLDL score. The
authors emphasize, however, that 9% of the patients had no oxLDL in
their valves, which might indicate that oxLDL is a contributor but not a
requisite for the development of AS.
Nalini M. Rajamannan: For patients who do not have a genetic abnormality,
most authorities agree that the traditional cardiovascular risk factors are
critical in the initiation event for this disease. The early histopathologic
findings in these patients are critical for the development of animal models,
and future medical therapies. Patients with familial hypercholesterolemia also
develop aortic valve disease. Sprecher DL, Schaefer EJ, Kent KM, et al.
Cardiovascular features of homozygous familial hypercholesterolemia: analysis of 16 patients. Am J Cardiol 54(1):20-30, 1984; Rajamannan NM,
Edwards WD, Spelsberg TC. Hypercholesterolemic aortic-valve disease.
N Engl J Med 349(7):717-8, 2003.
Oxidative Stress
Analogous to the role of oxidative stress in atherosclerosis, oxidant
generation was confirmed in human AS.66-68 Superoxide and hydrogen
peroxide levels were significantly elevated in calcified regions of stenotic
valves, but the process might be different from oxidant generation in
atherosclerosis, namely by reduced expression and activity of antioxidant
enzymes and possibly NOS uncoupling instead of NADPH oxidase
activity.66-68 Whether peroxide upregulates Msx2, Wnt/␤-catenin, and
runx2/cbfa-1 as in vascular osteochondrogenic mineralization,69 needs
further research. We hypothesize that oxidative stress might affect
calcification/osteogenesis through different pathways and cell types
during the evolution of AS, as the dominant cell types may vary at
different stages of the disease.
Nalini M. Rajamannan: The authors have clearly defined the different
potential pathways for the development of this disease as described in this
paragraph and also shown in Fig 1.
Mineralization and Bone Formation
Both calcific noduli and mature bone formation appear in AS, with
calcific noduli being the first to be described in the era when calcification
Curr Probl Cardiol, June 2010
297
was still considered passive, and later linked to plasma calcium and
parathyroid hormone, with and without renal disease.70-72 To date calcific
noduli are known to be initiated by macrophage- and obVIC-vesicles, and
by apoptosis of aVICs, in response to (inflammatory) chemokines. Bone
formation was described later, with presence of obVICs and upregulation
of the osteoblast and bone markers osteopontin, bone sialoprotein,
osteocalcin, alkaline phosphatase, and the osteoblast-specific transcription factor runx2/cbfa-1.73,74 The pathways modulating osteogenesis in
AS known to date consist of Lrp-5/Wnt/␤-catenin,75 osteoprotegerin/
rankl/RANK,76,77 tenascin-C,78 Toll-like receptors 2 and 4,79,80 and
angiotensin II, formed by chymase and cathepsin G from mast cells,81 and
by ACE colocalizing with apolipoproteins.82 All pathways are considered
potential new drug targets and subject to research. The exact timing of
and contribution to calcification and bone formation in vivo needs to be
further mapped.
Nalini M. Rajamannan: The presence of osteoblastogenesis in the calcified
aortic valve presents the foundation for the future experimental studies in this
field. Further understanding the timing of the cellular pathways provides the
future direction for the experimental studies in this field.
Inflammatory Mechanisms of Degeneration
Inflammation covers in AS the “cooperation” of endothelium, leukocytes, VICs, oxLDL,83 matrix and neo-angiogenesis as described above.
Via a TGF␤1-dependent pathway (among others) the endothelium expresses adhesion molecules, facilitating uptake of LDL, lymphocytes,
monocytes/macrophages, mast cells, and possibly pVICs. oxLDL might
also in valvular endothelium upregulate caveolin-1 and consequently
maintain the expression of endothelial adhesion molecules, and activate
macrophages. qVICs might transform to aVICs and obVICS in response
to inflammatory chemokines, with TGF␤ again as main player, and an
emerging role for Toll-like receptors. Neoangiogenesis further facilitates
inflammation, serving as highway to the leaflet matrix.84
Genetics
Last but not least, all the above-mentioned players in aortic valve
pathobiology are subject to genetic variations, from which only the top of
the iceberg is visible to date. Regarding bone metabolism, vitamin D
receptor polymorphisms and a nonsense mutation with haploinsufficiency
298
Curr Probl Cardiol, June 2010
in Notch 1 have been described. The receptor B allele, leading to reduced
calcium absorption, bone loss, and higher parathormone levels, is more
frequent among patients with AS, from which we might deduct that
calcium mobilization from bone enhances aortic valve calcification.85
Because Notch 1 acts, among other functions, as a repressor of Runx2,
regulating osteoblast activity, a nonsense mutation might lead to diminished inhibition of calcium deposition.86 The Pvull polymorphism in the
estrogen receptor ␣ gene might facilitate aortic stenosis through dyslipidemia.87 Regarding lipid metabolism, only conflicting data about allelic
variants of apolipoproteins are published to date,88-90 while the results for
genetic variations in inflammation and cell cycle regulatory genes are
even more preliminary.91,92 The search for culprit genes should however
be continued, both for early diagnosis in patients with genetic predisposition or in siblings in case of familial AS, as for treatment optimization
guided by pharmacogenomics. The need is illustrated by a Finnish
necropsy study with microcalcifications in anatomically normal aortic
leaflets of young subjects,93 while the Finnish population is known for
limited genetic variation, and a French epidemiologic study suggesting an
autosomal-dominant inheritance, different from apoE or vitamin D
receptor genes.94
Hypothesis on Calcific Aortic Valve Stenosis
We hypothesize that all human individuals develop aortic sclerosis to a
certain (subclinical) degree, due to aging and longstanding mechanical
stress. However, only the patients with the appropriate genetic background and/or facilitating factors such as a bicuspid valve, smoking,
diabetes, hypertension, dyslipidemia, or renal dysfunction will progress to
severe AS within their lifespan, with an as reported variable rate of
progression.95-97 AS is the common endpoint of diverse pathophysiological processes, able to develop independently from oxLDL.
Why Did SEAS and SALTIRE Show No Effect on
Aortic Valve Stenosis Progression?
With the background provided, several possible reasons can be indicated. At first, the selected patients did not have dyslipidemia as
facilitating factor for the progression of AS, so the effect would only
depend on the pleiotropic effects of statins. Second, only patients with at
least mild stenosis were included. As such the dysfunctional stress
distribution and inflammation might already be self-perpetuating and
surpassing the beneficial effect of statins. This hypothesis is supported by
Curr Probl Cardiol, June 2010
299
the recent retrospective study of Antonini-Canterin et al, showing that
statins only reduced progression in aortic sclerosis and mild AS, not in
more advanced stages.98 Third, statins do not act on all pathways of AS
pathophysiology, which on top do not fully resemble atherosclerosis.
Last, but not least, plaque stabilization accounts for most of the beneficial
effects of statins in atherosclerosis, but plaque rupture as a cause of
symptoms is not an issue in AS. These trials are very valuable, however.
As they emerged from the internationally growing conviction that statins
alone could be capable of slowing the progression of AS, they can now
be seen as the catalysts for further maturation of AS research.
Nalini M. Rajamannan: LDL-Density-Radius Theory is a recently published
theory describing trial design for future valvular heart disease. This theory
incorporates the biology and the importance of the hemodynamic measurement for aortic valve disease using the continuity equation. Rajamannan NM.
Mechanisms of aortic valve calcification: the LDL-density-radius theory: a
translation from cell signaling to physiology. Am J Physiol Heart Circ Physiol
2009.
What Should Be the Next Step?
Further characterization of VICs and response to culture conditions is
warranted, to optimize in vitro experiments to search for and test new
drug targets, and test combinations and optimal timing of established
drugs (statins, ACE-inhibitors, angiotensin-receptor blockers). In parallel
the search for low cost animal models needs to be continued, at first to
completely characterize the evolution of AS, both by immunohistochemics as by in vivo molecular imaging, followed by testing the drug
regimens emerging from the in vitro experiments. Meanwhile, the genetic
background influencing the evolution of AS and response to pharmacotherapy should be further mapped, to direct further human trials. At
present statins are established players in cardiovascular prevention and
should be administered to AS patients with a current guidelines indication. To date statins cannot be advocated to patients solely to prevent
progression of AS. They might prove valuable as part of a drug regimen,
as lipids are an important but not the only player in AS, taking into
account timing and genetic background of the patient.
Nalini M. Rajamannan: In summary, the authors have summarized the field
of calcific aortic valve disease from experimental models to clinical trials
extremely well. This paper demonstrates the potential for future experimental
and clinical studies in this field. The authors have carefully reviewed the
300
Curr Probl Cardiol, June 2010
published data and have defined numerous mechanisms for this disease. In
the future, medical therapy for calcific aortic valve disease will have many
signaling pathways to target to try and slow progression of this disease.
REFERENCES
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
Lindroos M, Kuppari M, Heikkilä J, et al. Prevalence of aortic valve abnormalities
in the elderly: an echocardiographic study of a random population sample. J Am
Coll Cardiol 1993;21(5):1220-5.
Vahanian A, Baumgartner H, Bax J, et al. Guidelines on the management of
valvular heart disease: the Task Force on the Management of Valvular Heart
Disease of the European Society of Cardiology. Eur Heart J 2007;28(2):230-68.
Aronow WS, Ahn C, Kronzon I, et al. Association of coronary risk factors and use
of statins with progression of mild valvular aortic stenosis in older persons. Am J
Cardiol 2001;88(6):693-5.
Novaro GM, Tiong I, Pearce GL, et al. Effect of hydroxymethylglutaryl coenzyme
A reductase inhibitors on the progression of calcific aortic valve stenosis.
Circulation 2001;104:2205-9.
Bellamy MF, Pellikka PA, Klarich KW, et al. Association of cholesterol levels,
hydroxymethylglutaryl coenzyme A reductase inhibitor treatment, and progression
of aortic stenosis in the community. J Am Coll Cardiol 2002;40:1723-30.
Shavelle DM, Takasu J, Budoff MJ, et al. HMG CoA reductase inhibitor (statin)
and aortic valve calcium. Lancet 2002;359(9312):1125-6.
Rosenhek R, Rader F, Loho N, et al. Statins but not angiotensin-converting enzyme
inhibitors delay progression of aortic stenosis. Circulation 2004;110:1291-5.
Moura LM, Ramos SF, Zamorano JL, et al. Rosuvastatin affecting aortic valve
endothelium to slow the progression of aortic stenosis. J Am Coll Cardiol 2007;
49:554-61.
Pohle K, Mäffert R, Ropers D, et al. Progression of aortic valve calcification.
Association with coronary atherosclerosis and cardiovascular risk factors. Circulation 2001;104:1927-32.
Rossebø AB, Pedersen T, Boman K, et al. Intensive lipid lowering with simvastatin
and ezetimibe in aortic stenosis. N Engl J Med 2008;359:1343-56.
Cowell SJ, Newby DE, Prescott RJ, et al. A randomized trial of intensive
lipid-lowering therapy in calcific aortic stenosis. N Engl J Med 2005;352:2389-97.
Lindroos M, Kupari M, Valvanne J, et al. Factors associated with calcific aortic
valve degeneration in the elderly. Eur Heart J 1994;15(7):865-70.
Stewart BF, Siscovick D, Lind BK, et al. Clinical factors associated with calcific
aortic valve disease. Cardiovascular health study. J Am Coll Cardiol 1997;29:
630-4.
Iung B, Baron G, Butchart EG, et al. A prospective survey of patients with valvular
heart disease in Europe: the Euro heart survey on valvular heart disease. Eur Heart J
2003;24:1231-43.
Olsson M, Dalsgaard CJ, Haegerstrand A, et al. Accumulation of T-lymphocytes
and expression of interleukin-2 receptors in nonrheumatic stenotic aortic valves.
J Am Coll Cardiol 1994;23(5):1162-70.
Curr Probl Cardiol, June 2010
301
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
302
Otto CM, Kuusisto J, Reichenbach DD, et al. Characterization of the early lesion
of degenerative valvular aortic stenosis. Histological and immunohistochemical
studies. Circulation 1994;90:844-53.
O’Brien KD, Reichenbach DD, Marcinova SM, et al. Apolipoproteins B, (a), and
E accumulate in the morphologically early lesion of degenerative valvular aortic
stenosis. Arterioscler Thromb Vasc Biol 1996;16:523-32.
Rajamannan NM, Subramaniam M, Springett M, et al. Atorvastatin inhibits
hypercholesterolemia-induced cellular proliferation and bone matrix production in
the rabbit aortic valve. Circulation 2002;105:2660-5.
Simmons CA, Grant GR, Manduchi E, et al. Spatial heterogeneity of endothelial
phenotypes correlates with site-specific vulnerability to calcification in normal
porcine aortic valves. Circ Res 2005;96:792-9.
Vasile E, Antohe F. An ultrastructural study of beta very low density lipoprotein
uptake and transport by valvular endothelium of hyperlipidemic rabbits. J Submicrosc Cytol Pathol 1991;23:279-87.
Nievelstein-Post P, Mottino G, Fogelman A, et al. An ultrastructural study of
lipoprotein accumulation in cardiac valves of the rabbit. Arterioscler Thromb
1994;14:1151-61.
Rajamannan NM, Sangiorgi G, Springett M, et al. Experimental hypercholesterolemia induces apoptosis in the aortic valve. J Heart Valve Dis 2001;10:371-4.
Drolet MC, Arsenault M, Couet J. Experimental aortic valve stenosis in rabbits.
J Am Coll Cardiol 2003;41:1211-7.
Cimini M, Boughner DR, Ronald JA, et al. Development of aortic valve stenosis in
a rabbit model of atherosclerosis: an immunohistochemical and histological study.
J Heart Valve Dis 2005;14:365-75.
Zeng Z, Nievelstein-Post P, Yin Y, et al. Macromolecular transport in heart valves
III: experiment and theory for the size distribution of extracellular liposomes in
hyperlipidemic rabbits. Am J Physiol Heart Circ Physiol 2007;292:H2687-97.
Luo G, Ducy P, McKee MD, et al. Spontaneous calcification of arteries and
cartilage in mice lacking matrix gla protein. Nature 1997;386:78-81.
Galvin KM, Donovan MJ, Lynch CA, et al. A role for SmadVI in development and
homeostasis of the cardiovascular system. Nat Genet 2000;24:171-4.
Lee TC, Zhao YD, Courtman DW, et al. Abnormal aortic development in mice
lacking endothelial nitric oxide synthase. Circulation 2000;101:2345-8.
Tanaka K, Sata M, Fukuda D, et al. Age-associated aortic stenosis in apolipoprotein
E-deficient mice. J Am Coll Cardiol 2005;46:134-41.
Garg V, Muth AN, Ransom JF, et al. Mutations in NOTCH 1 cause aortic valve
disease. Nature 2005;437:270-4.
Drolet MC, Roussel E, Deshaies Y, et al. A high fat/high carbohydrate diet induces
aortic valve disease in C57BL/6J mice. J Am Coll Cardiol 2006;47:850-5.
Weiss RM, Ohashi M, Miller JD, et al. Dl. Calcific aortic valve stenosis in old
hypercholesterolemic mice. Circulation 2006;114:2065-9.
Aikawa E, Nahrendorf M, Sosnovik D, et al. Multimodality molecular imaging
identifies proteolytic and osteogenic activities in early aortic valve disease. Circulation
2007;115:377-86.
Davignon J. Beneficial cardiovascular pleitropic effects of statins. Circulation
2004;109(suppl III):III-39-III-43.
Curr Probl Cardiol, June 2010
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
47.
48.
49.
50.
51.
52.
Soini Y, Salo T, Satta J. Angiogenesis is involved in the pathogenesis of
nonrheumatic aortic valve stenosis. Hum Pathol 2003;34(8):756-63.
Rajamannan NM, Subramaniam M, Rickard D, et al. Human aortic valve
calcification is associated with an osteoblast phenotype. Circulation 2003;107:
2181-4.
Roberts WC, Ko JM. Frequency by decades of unicuspid, bicuspid and tricuspid
aortic valves in adults having isolated aortic valve replacement for aortic stenosis,
with or without associated regurgitation. Circulation 2005;111:920-5.
Thubrikar MJ, Aouad J, Nolan SP. Patterns of calcific deposits in operatively
excised stenotic or purely regurgitant aortic valves and their relation to mechanical
stress. Am J Cardiol 1986;58(3):304-8.
Nicosia MA, Cochran RP, Reichenbach DR, et al. A coupled fluid-structure
finite-element model of the aortic valve and root. J Heart Valve Dis 2003;12:781-9.
Davignon J, Ganz, P. Role of endothelial dysfunction in atherosclerosis. Circulation
2004;109(suppl lIII):III-27-III-32.
Tiwari RL, Singh V, Barthwal MK. Macrophages: an elusive yet emerging
therapeutic target of atherosclerosis. Med Res Rev 2008;28(4):483-544.
Robicsek F, Thubrikar MJ, Fokin AA. Cause of degenerative disease of the
trileaflet valve: review of the subject and presentation of a new theory. Ann Thorac
Surg 2002;73:1346-54.
Singh R, Strom JA, Ondrovic L, et al. Age-related changes in the aortic valve affect
leaflet stress distributions: implications for aortic valve degeneration. J Heart Valve
Dis 2008;17(3):290-8.
Sacks MS, Yoganathan AP. Heart valve function: a biomechanical perspective.
Philos Trans R Soc Lond 2007;362:1369-91.
Balachandran K, Sucosky P, Jo H, et al. Elevated cyclic stretch alters matrix
remodelling in aortic valve cusps: implications for degenerative aortic valve
disease. Am J Physiol Heart Circ Physiol 2009;296:H756-764.
Merryman WD, Lukoff HD, Long RA, et al. Synergistic effects of cyclic tension
and transforming growth factor -␤1 on the aortic valve myofibroblast. Cardiovasc
Pathol 2007;16:268-76.
Sucosky P, Balachandran K, Elhammaly A, et al. Altered shear stress stimulates
upregulation of endothelial VCAM-1 and ICAM-1 in a BMP-4- and TGF␤1dependent pathway. Arterioscler Thromb Vasc Biol 2009;29:254-60.
El-Hamamsy I, Balachandran K, Yacoub MH, et al. Endothelium-dependent
regulation of the mechanical properties of aortic valve cusps. J Am Coll Cardiol
2009;53:1448-55.
Butcher JT, Penrod AM, Garcia AJ, et al. Unique morphology and focal adhesion
development of valvular endothelial cells in static and fluid flow environments.
Arterioscler Thromb Vasc Biol 2004;24:1429-34.
Butcher JT, Tressel S, Johnson T, et al. Transcriptional profiles of valvular and
vascular endothelial cells reveal phenotypic differences. Influence of shear stress.
Arterioscler Thromb Vasc Biol 2006;26:69-77.
Liu AC, Joag VR, Gotlieb AI. The emerging role of valve interstitial cell
phenotypes in regulating heart valve pathobiology. Am J Pathol 2007;171:1407-18.
Paranya G, Vineberg S, Dvorin E, et al. Aortic valve endothelial cells undergo
transforming-growth-factor-␤-mediated and non-transforming-growth-factor␤-mediated transdifferentiation in vitro. Am J Pathol 2001;159:1335-43.
Curr Probl Cardiol, June 2010
303
53.
54.
55.
56.
57.
58.
59.
60.
61.
62.
63.
64.
65.
66.
67.
68.
69.
304
Paruchuri S, Yang JH, Aikawa E, et al. Human pulmonary valve progenitor cells
exhibit endothelial/mesenchymal plasticity in response to vascular endothelial
growth factor-A and transforming-growth-factor-␤2. Circ Res 2006;99:861-9.
Yip CYY, Chen JH, Zhao R, et al. Calcification by valve interstitial cells is
regulated by the stiffness of the extracellular matrix. Arterioscler Thromb Vasc Biol
2009;29:936.
Monzack EL, Gu X, Masters KS. Efficacy of simvastatin treatment of valvular
interstitial cells varies with the extracellular environment. Arterioscler Thromb
Vasc Biol 2009;29:246-53.
Wu B, Elmariah S, Kaplan FS, et al. Paradoxical effects of statins on aortic valve
myofibroblasts and osteoblasts. Implications for end-stage valvular heart disease.
Arterioscler Thromb Vasc Biol 2005;25:592-7.
Anger T, El-Chafchak J, Habib A, et al. Statins stimulate RGS-regulated ERK ½
activation in human calcified and stenotic aortic valves. Exp Mol Pathol 2008;
85:101-11.
Edep ME, Shirani J, Wolf P, et al. Matrix metalloproteinase expression in
nonrheumatic aortic stenosis. Cardiovasc Pathol 2000;9:281-6.
Fondard O, Detaint D, Iung B, et al. Extracellular matrix remodeling in human
aortic valve disease: the role of matrix metalloproteinases and their tissue
inhibitors. Eur Heart J 2005;26:1333-41.
Satta J, Oiva J, Salo T, et al. Evidence for an altered balance between matrixmetalloproteinase-9 and its inhibitors in calcific aortic stenosis. Ann Thorac Surg
2003;76:681-8.
Helske S, Syvaranta S, Lindstedt KA, et al. Increased expression of elasolytic
cathepsins S, K, V and their inhibitor cystatin C in stenotic aortic valves.
Arterioscler Thromb Vasc Biol 2006;26:1791-8.
Helske S, Syvaranta S, Kupari M, et al. Possible role for mast cell-derived
cathepsin G in the adverse remodeling of aortic valves. Eur Heart J 2006;
27:1495-504.
Kaden JJ, Dempfle CE, Grobholz R, et al. Inflammatory regulation of extracellular
matrix remodeling in calcific aortic valve stenosis. Cardiovasc Pathol 2005;14:
80-7.
Mohty D, Pibarot P, Després JP, et al. Association between plasma LDL particle
size, valvular accumulation of oxidized LDL, and inflammation in patients with
aortic stenosis. Arterioscler Thromb Vasc Biol 2008;28:187-93.
Warren BA, Yong JL. Calcification of the aortic valve: its progression and grading.
Pathology 1997;29(4):360-8.
Chen K, Thomas SR, Keaney JF Jr, et al. Oxidation: ROS in vascular signal
transduction. Free Radic Biol Med 2003;35:117-32.
Miller JD, Chu Y, Brooks RM, et al. Dysregulation of antioxidant mechanisms
contributes to increased oxidative stress in calcific aortic valvular stenosis in
humans. J Am Coll Cardiol 2008;52:843-50.
Liberman M, Bassi E, Martinatti MK, et al. Oxidant generation predominates
around calcifying foci and enhances progression of aortic valve calcification.
Arterioscler Thromb Vasc Biol 2008;28:463-70.
Towler DA. Oxidation, inflammation, and aortic valve calcification. J Am Coll
Cardiol 2008;52:851-4.
Curr Probl Cardiol, June 2010
70.
71.
72.
73.
74.
75.
76.
77.
78.
79.
80.
81.
82.
83.
84.
85.
86.
Maher ER, Young G, Smyth-Walsh B, et al. Aortic and mitral valve calcification
in patients with end-stage renal disease. Lancet 1987;2(8564):875-7.
Ortlepp JR, Pillich M, Schmitz F, et al. Lower serum calcium levels are
associated with greater calcium hydroxyapatite deposition in native aortic
valves of male patients with severe calcific aortic stenosis. J Heart Valve Dis
2006;15(4):502-8.
Linhartova K, Veselka J, Sterbakova G, et al. Parathyroid hormone and vitamin D
levels are independently associated with calcific aortic stenosis. Circ J 2008;72:
245-50.
O’Brien KD, Kuusisto J, Reichenbach DD, et al. Osteopontin is expressed in
human aortic valvular lesions. Circulation 1995;92:2163-8.
Mohler ER III, Gannon F, Reynolds C, et al. Bone formation and inflammation in
cardiac valves. Circulation 2001;103:1522-8.
Caira FC, Stock SR, Gleason TG, et al. Human degenerative valve disease is
associated with up-regulation of low-density lipoprotein receptor-related protein-5
receptor-mediated bone formation. J Am Coll Cardiol 2006;47:1707-12.
Kaden JJ, Bickelhaupt S, Grobholz R, et al. Receptor activator of nuclear factor kB
ligand and osteoprotegerin regulate aortic valve calcification. J Mol Cell Cardiol
2004;36:57-66.
Steinmetz M, Skowasch D, Wernert N, et al. Differential profile of the OPG/
RANKL/RANK system in degenerative aortic native and bioprosthetic valves.
J Heart Valve Dis 2008;17(2):187-93.
Satta J, Melkko J, Pöllänen R, et al. Progression of human aortic valve stenosis is
associated with tenascin-C expression. J Am Coll Cardiol 2002;39:96-101.
Meng X, Ao L, Song Y, et al. Expression of functional toll-like receptors 2 and 4
in human aortic valve interstitial cells: potential roles in aortic valve inflammation
and stenosis. Am J Physiol Cell Physiol 2008;294:C29-35.
Yang X, Fullerton DA, Su X, et al. Pro-osteogenic phenotype of human aortic valve
interstitial cells is associated with higher levels of toll-like receptors 2 and 4 and
enhanced expression of bone morphogenic protein 2. J Am Coll Cardiol 2009;
53(6):491-500.
Helske S, Lindstedt KA, Laine M, et al. Induction of local angiotensin II producing
systems in stenotic aortic valves. J Am Coll Cardiol 2004;44:1859-66.
O’Brien KD, Shavelle DM, Caulfield MT, et al. Association of angiotensinconverting enzyme with low-density lipoprotein in aortic valvular lesions and in
human plasma. Circulation 2002;106:2224-30.
Holvoet P, De Keyzer D, Jacobs DR, et al. And the metabolic syndrome. Futures
Lipidol 2008;3(6):637-49.
Mazzone A, Epistolato MC, De Caterina R, et al. Neoangiogenesis, T-lymphocyte
infiltration, and heat shock protein- 60 are biological hallmarks of an immunomediated inflammatory process in end-stage calcified aortic valve stenosis. J Am Coll
Cardiol 2004;43:1670-6.
Ortlepp JR, Hoffmann R, Ohme F, et al. The vitamin D receptor genotype
predisposes to the development of calcific aortic valve stenosis. Heart 2001;85:
635-8.
Garg V, Muth AN, Ransom JF, et al. Mutations in Notch 1 cause aortic valve
disease. Nature 2005;437:270-4.
Curr Probl Cardiol, June 2010
305
87.
88.
89.
90.
91.
92.
93.
94.
95.
96.
97.
98.
306
Nordström P, Glader CA, Dahlen G, et al. Oestrogen receptor alpha gene
polymorphism is related to aortic valve sclerosis in postmenopausal women.
J Intern Med 2003;254:140-6.
Novaro GM, Sachar R, Pearce GL, et al. Association between apolipoprotein E
alleles and calcific valvular heart disease. Circulation 2003;108:1804-8.
Avakian SD, Annicchino-Bizzacchi JM, Grinberg M, et al. Apolipoproteins AI, B,
and E polymorphisms in severe aortic valve stenosis. Clin Genet 2001;60:381-4.
Ortlepp JR, Pillich M, Mevissen V, et al. ApoE alleles are not associated with
calcific aortic stenosis. Heart 2006;92:1463-6.
Ortlepp JR, Schmitz F, Mevissen V, et al. The amount of calcium-deficient
hexagonal hydroxyapatite in aortic valves is influenced by gender and associated
with genetic polymorphisms in patients with severe calcific aortic stenosis. Eur
Heart J 2004;25:514-22.
Golubnitschaja O, Yeghiazaryan K, Skowasch D, et al. P21WAF1/CIP1 and 14-3-3
sigma gene expression in degenerated aortic valves: a link between cell cycle
checkpoints and calcification. Amino Acids 2006;31:309-16.
Kuusisto J, Räsänen K, Särkioja T, et al. Atherosclerosis-like lesions of the aortic
valve are common in adults of all ages: a necropsy study. Heart 2005;91:576-82.
Probst V, Le Scouarnec S, Legendre A, et al. Familial aggregation of calcific aortic
valve stenosis in the western part of France. Circulation 2006;113:856-60.
Roger VL, Tajik AJ, Bailey, KR, et al. Progression of aortic stenosis in adults: new
appraisal using Doppler echocardiography. Am Heart J 1990;119:331-8.
Rosenhek R, Klaar U, Schemper M, et al. Mild and moderate aortic stenosis.
Natural history and risk stratification by echocardiography. Eur Heart J 2004;25:
199-205.
Briand M, Lemieux I, Dumesnil JG, et al. Metabolic syndrome negatively
influences disease progression and prognosis in aortic stenosis. J Am Coll Cardiol
2006;47:2229-36.
Antonini-Canterin F, Hirsu M, Popescu BA, et al. Stage-related effect of statin
treatment on the progression of aortic valve sclerosis and stenosis. Am J Cardiol
2008;102:738-42.
Curr Probl Cardiol, June 2010