Overview of the current animal models for heart
failure
The second challenge for HF preclinical research is the selection of the
experimental model. Several previous and recent reviews provide a
framework for the present discussion (Gomes, Falcao-Pires, Pires,
Brás-Silva, & Leite-Moreira, 2013; Houser et al., 2012; Patten &
Hall-Porter, 2009; Riehle & Bauersachs, 2019; Y.-T. Shen et al., 2017;
Silva & Emter, 2020). Building on these works, we introduced current
preclinical animal models according to the most common triggers for HF,
including ischemia, hypertension, dilated cardiomyopathy and valve
disease. Since the process of generating various animal models has been
described in many previous studies, we refrain from a detailed
description of each modeling method. Instead, we emphasize the pathology
features of HF that can be presented by the model and their application
limitations (Figure 1, Table 2 ). Additionally, we summarized
significant changes of hemodynamics and echocardiography derived
parameters in each animal model (Table 2 ), which would provide
practical guidance for researchers who considering preclinical studies
for the treatment of HF.
3.1 HF induced by myocardial
ischemia
Myocardial ischemia is one of the most common causes of HF, the
imbalance between myocardial blood supply and demand can be spontaneous
or precipitated by coronary artery disease (e.g., atherosclerosis or
thrombosis) or can occur during periprocedural revascularization surgery
performed to restore spontaneous ischemia (e.g., percutaneous coronary
intervention or coronary artery bypass grafting) (Thygesen, Alpert,
White, & Infarction, 2007). There are three main techniques in the
model of HF induced by myocardial ischemia/infarction: permanent
(irreversible) coronary occlusion, ischemia/reperfusion and coronary
microembolization. Consistent with the progress of clinical patients,
these three techniques combine the characteristics of HF induced by
myocardial ischemia, including the initial ischemic event, followed by
decreased cardiac output and ejection fraction, eccentric hypertrophy,
focal fibrosis in the ischemic area, activation of neurohormone system
and decrease of cardiac reserve (Houser et al., 2012). Correctly
identifying the response of different types of myocardial infarction to
ischemia is not only paramount for optimizing the management of
patients, but also an important feature to simulate the transformation
study of acute myocardial infarction induced HF.
3.1.1 Permanent coronary artery
occlusion
Coronary artery ligation that simulates myocardial infarction (MI) is
the most commonly used model of HF in small animals, which was first
described in mice by Zolotareva et al (Zolotareva & Kogan, 1978). After
that, the pioneering study in rats by Pfeffer et al.(J. M. Pfeffer,
Pfeffer, & Braunwald, 1985) proved that infarct size, post-MI LV
chamber dilatation and LV function are correlated. Their subsequent
findings regarding the improvement of Captopril (an ACE inhibitor) on
the contractile function and survival rate of rats (M. Pfeffer, Pfeffer,
Steinberg, & Finn, 1985) and patients (M. A. Pfeffer et al., 1992)
after myocardial infarction, contribute to the establishment of the
pharmacological ACE inhibitor treatment strategy, which has become a
standard first-line treatment for HF.
As is well known, the infarct size is closely related to the duration of
coronary artery occlusion. In most species, the shortest time required
for coronary artery occlusion to induce MI should not be less than 20-30
minutes, which provides a definite and smallest size of MI. In the study
of coronary artery ligation in small animals, the surviving mice
gradually developed into HF during the 2.5 - 9 week period post-surgery
(Gao, Dart, Dewar, Jennings, & Du, 2000). The infarct size varies
significantly from 15.2% to 55.2% of the left ventricle mass, which is
directly related to the degree of left ventricular dysfunction and
affects the time course of HF development (Gao et al., 2000; M. A.
Pfeffer et al., 1979). Rats with infarctions greater than 46% had
congestive heart failure, with elevated filling pressures, reduced
cardiac output, and a minimal capacity to respond to pre- and after load
stresses. In addition, other factors, including age (Gould et al.,
2002), sex (Wu, Nasseri, Bloch, Picard, & Scherrer-Crosbie, 2003) and
genetic background (van den Borne et al., 2009) of animals also exert
complex integrated effects on the time course of HF development induced
by this model.
In large animals, such as pigs and sheep, irreversible coronary
occlusion can be performed in the left anterior descending coronary
artery (LAD) or left circumflex coronary artery (LCx) by acute
ligation(Van der Velden et al., 2004), or
thrombogenic coil (CHARLES,
ELLIOTT, NICHOLLS, RADEMAKER, & RICHARDS, 2000), hydraulic occlude (Y.
T. Shen & Vatner, 1996) and ameroid constrictor (Chekanov et al., 2003;
O’konski, White, Longhurst, Roth, & Bloor, 1987) placement. The former
is an immediate approach to develop acute MI, whereas hydraulic occlude,
thrombogenic coil or ameroid constrictors placement can mimic MI
resulting from coronary stenosis due to progressive atherosclerotic
plaque formation. These methods can produce phenotypes similar to those
of small animals, including the initial observation of MI and the
subsequent induction of a significant decrease of ejection fraction by
25% to 35% (J. Zhang et al., 1996). Besides, this model can also
increase LV weight and LV end-diastolic area. It is worth noting that
the location of coronary artery occlusion or ligation is related to the
infarct size. In pigs or dogs, compared with LCx ligation, LAD occlusion
leads to a relatively larger infarct size(Becker, Schuster, Jugdutt,
Hutchins, & Bulkley, 1983). Additionally, infarct size differs among
species and among lines of the same species in this model. For instance,
beagle dogs have a larger infarct size than mongrel dogs(Uemura et al.,
1989). Other studies that examined obese Ossabaw swine by LCx ameroid
constrictor placement resulted in a model of chronic ischemia as opposed
to MI-induced HF because no or minimal subendocardial signs of
infarction were observed (Elmadhun, Lassaletta, Chu, & Sellke, 2013).
One potential limitation of the irreversible coronary occlusion animal
model is permanent occlusion of myocardial vascular flow, which is
contrary to the clinical features of patients with progressive
non-occlusive coronary artery occlusion. Patients have infarct-related
arteries due to spontaneous thrombolysis or reperfusion by fibrinolytic
enzyme or balloon angioplasty, which cannot be reproduced in this model.
In addition, this model has a high mortality rate due to acute heart
failure or LV rupture within the first week post-MI (Gao et al., 2000).
3.1.2 Ischemia-reperfusion
model
To overcome the limitations of irreversible coronary artery occlusion in
animal model, ischemia/reperfusion (I/R) models have been established in
different species. Ischemia/reperfusion will block the coronary blood
flow to the myocardium and then reintroduce the blood flow into the
ischemic area. This is helpful to study the molecular mechanisms and
tissue damage after temporary occlusion of LAD. Compared with permanent
left anterior descending branch occlusion, ischemia/reperfusion model
shows less tissue damage compared to permanent LAD occlusion. Advantages
of this model include a high survival rate, adjustable MI size according
to coronary artery occlusion site, reproducible cardiac dysfunction and
relatively low invasive methods (Bikou, Watanabe, Hajjar, & Ishikawa,
2018).
Lots of works has been carried out on I/R model in small animals
(Michael et al., 1995; Podesser et al., 2002; Reitz et al., 2019;
Shimizu et al., 2018), from which left coronary artery occlusion for
45-60 minutes followed by reperfusion usually leads to HF 4 weeks
post-surgery in mice (Reitz et al., 2019; Shimizu et al., 2018), with
signs of HF including increased left ventricular (LV) internal diastolic
(LVIDd) and systolic (LVIDs) dimensions, along with decreased ejection
fraction (% EF) and fractional shortening (% FS) (Reitz et al., 2019).
In large animals, I/R is commonly used in left anterior LAD or LCx,
which is produced by reversible ligation or inflation of an
intracoronary angioplasty balloon (Bikou et al., 2018). Although dogs
have been used for I/R research in history, the extensive coronary
collateral circulation in canine hearts limits the use of this model. As
pigs and sheep share the similar coronary arteries as humans (including
gross anatomical structure and absence of existing collateral vessels),
the I/R approach can be used to induce infarcts of predictable size and
location in these species (Y.-T. Shen et al., 2017). Moreover, the
infarct size produced by I/R may vary with different surgical sites, in
general, using the I/R protocol of proximal occlusion of LAD would lead
to more serious diseases, which indicates that it may be a better
preclinical model (Ishikawa et al., 2014). The pathological features of
HF induced by I/R include the acute increase of natriuretic peptide
level and cardiac troponin T, the progressively increased LV volume and
the decreased EF (CHARLES et al., 2000). Limitations of pig and sheep
I/R models include severe acute susceptibility to arrhythmia, and
difficulty in imaging the heart with ultrasound techniques due to
differences in ruminant dependence in gastrointestinal anatomy.
3.1.3 Coronary
microembolization
Repeated coronary microembolization not only avoids the risk of severe
acute myocardial infarction, but also mimics the chronic ischemic
process caused by repeated ischemic injury. Contrary to coronary artery
ligation or ameroid constrictor placement, HF with different degrees of
left ventricular dysfunction can be produced in closed chest model by
repeated coronary microembolization. This protocol has been investigated
in very distinct species, but predominantly apply to the practices of
translational study in large animals, by injecting glass (Franciosa,
Heckel, Limas, & Cohn, 1980) or polystyrene microspheres(Sabbah et al.,
1991) (with various diameters depend on materials) into the LAD or LCx
coronary artery. The regional contractile dysfunction induced by
microspheres is proportionate to the number of injected particles (Erbel
& Heusch, 2000). In a study on canine model three months post-surgery
(Sabbah et al., 1991), reductions in cardiac output and function were
observed and were associated with a transmural MI distributed throughout
the LV, septum, and right ventricle. Signs of HF include decreased EF,
LV dilatation (increased end diastolic volume), increased pulmonary
artery wedge pressure, systemic vascular resistance and plasma atrial
natriuretic peptide and/or norepinephrine. This model has been
successfully used in many pharmacological studies aimed at preventing
the remodeling process of LV failure. In a separate study, Sabbah et al.
showed dopamine β -hydroxylase treatment can reduce the continuous
increase of end diastolic and end systolic volumes, thus preventing
progressive LV dysfunction and remodeling (Sabbah et al., 2000). In
another similar study, long-term treatment with bosentan (a mixed
endothelin-1 receptor antagonist A and B) can prevent the progress of LV
dysfunction and weaken LV chamber remodeling in dogs with moderate HF
induced by multiple consecutive intracoronary embolization (Mishima et
al., 2000).
Repeated coronary microembolization can mimic the chronic effect of
myocardial ischemia increasing with time. However, this process requires
an intracoronary injection technique, which is usually performed under
the anesthesia of a special catheter inserted into a specific area or
implanted into a coronary artery for a long time. In addition, it is
difficult to find a consistent protocol for the number of injections and
the amount of microembolization (Y.-T. Shen et al., 2017). Therefore,
this model is not easy to be repeated by most laboratories.
3.2 HF induced by systemic
hypertension
In the United States, 46% of adults suffer from hypertension, which is
the main risk factor for brain, heart and kidney events (Virani et al.,
2020). Moreover, 17% of patients with HF were induced by hypertension
(Virani et al., 2020). In understanding that hypertension
pathophysiology is complex and not definitive, it is difficult to
establish an animal model simulating clinical hypertension.
3.2.1 Transgenic animal models
The most widely used model of HF induced by hypertension is transgenic
animal models, including spontaneously hypertensive rat (SHR),
spontaneously hypertensive HF (SHHF) rat and DS rat, etc.
As early as 1960s, Okamoto et al. (Okamoto & Aoki, 1963) have produced
spontaneously hypertensive rat (SHR), which is a natural model of
pressure overload. Systemic hypertension in SHR mice gradually attacks
with age and leads to obvious CHF at the age of 18–24 months, which is
characterized by increased end-diastolic and end-systolic volumes and
depressed EF in LV (Bing et al., 1995). With these features, this model
is suitable for studying the transition from hypertrophy to CHF and
replicating CHF induced by hypertension in human. On the basis of SHR
mice, a further developed subspecies, SHR stroke prone (SHR-SP), was
developed, which would quickly develop severe hypertension with salt
diet and has a strong tendency to die of stroke within a few weeks
(Yamori, 1991). Another commonly used Transgenic lines for HF study is
Spotaneously Hypertensive HF (SHHF) rat, which carry the facpobesity gene that encodes a defective leptin gene, to enable them
develop noninsulin-dependent diabetes mellitus, obesity, hypertension
and CHF (McCune, Baker, & Stills Jr, 1990; McCune, Park, Radin, &
Jurin, 1995). Of notice, the time course for the development of HF
depends on the dosage of facp gene (McCune et al., 1995).
Besides, hypertension, plasma renin activity and male gender are
independent factors contributing to cardiac hypertrophy and HF in this
rat model (Holycross, Summers, Dunn, & McCune, 1997). When compared to
SHR rats, SHHF rats would have suffer from HF earlier with loss of
cardiac function begins at age of 15 months (Heyen et al., 2002). And
similar to SHRs, male animals are more likely to suffer from HF than
female animals (Park, Liu-Stratton, Medeiros, Mccune, & Radin, 2004).
During the same period SHR rat emerged, a model of salt sensitivity,
namely the Dahl-salt-sensitive (DS) rat was also developed,
characterized by susceptibility to develop different degrees of
hypertension depending on the variations in sodium intake (Dahl, Heine,
& Tassinari, 1962). DS rats fed with high diet at age of 7 or 8 week
would develop different phenotypes of hypertensive heart failure (Doi et
al., 2000), which is suitable for studying the transition from
compensatory hypertrophy to failure. Generally speaking, the main
advantage of these models is that they avoid the complications related
to surgery or drug intervention, and can imitates the clinicopathologic
features of HF induced by human essential hypertension.
3.2.2 Renal artery stenosis
In addition to genetic animal models, the most direct way to mimic the
pathological changes of patients with hypertension is to perform surgery
through kidney clipping or wrapping. As early as 1934, since Goldblatt
et al. introduced an elevation of blood pressure by constriction of both
main renal arteries of dog (Goldblatt, Lynch, Hanzal, & Summerville,
1934), the Goldblatt Hypertension method (including Two-kidney, one clip
[2K1C] and one-kidney, one clip [1K1C] hypertension) has been
extensively studied and was successfully applied to the renal induced
models of hypertension in rats (Junhong et al., 2008), rabbits (Kumagai,
Suzuki, Ryuzaki, Matsukawa, & Saruta, 1990) and sheep(Lau et al.,
2010). Animal undergo 2K1C or 1K1C surgery would induce clinical signs
of HF. In a rat model study, 2K1C can induce systemic hypertension and
LV concentric remodeling within 8 weeks (Junhong et al., 2008). In
another, 1K1C on sheep for 3-11 weeks showed elevated blood pressure,
enlarged LA and reduced LAEF (Lau et al., 2010). Another model named
”Page model”, which can be produced by wrapping one or both kidneys in
cellophane, has been historically used for dogs to develop systemic
hypertension (Page, 1939). Systemic hypertension induced by bilateral
renal wrapping on aged dogs can model several aspects of structural and
functional characteristics described in the limited studies of human
diastolic HF, including LV hypertrophy, myocardial fibrosis, and
isolated diastolic dysfunction, which provides insight into the
pathogenesis of diastolic HF (Munagala, Hart, Burnett Jr, Meyer, &
Redfield, 2005).
3.3 HF failure induced by dilated
cardiomyopathy
The phenotype of Dilated cardiomyopathy (DCM) is induced by many primary
and secondary causes(Houser et al., 2012). Primary diseases only affect
myocardium (idiopathic DCM), whereas secondary causes are extensive,
with most commonly clinical signs being coronary artery disease,
myocardial infarction (ischemic cardiomyopathy) and long-term
hypertension. Other causes include myocarditis (especially viral),
chemotherapy drugs (such as anthracyclines), persistent and
inappropriate tachycardia, etc. Consistent with these clinical
incentives, DCM can be induced by the above-mentioned ischemic
injury/myocardial infarction and systemic hypertension, as well as toxic
injury, rapid ventricular pacing, pressure overload and volume overload
described below. These models can be used to define hemodynamic,
mechanical, neurohormonal, cellular and molecular changes during HF, and
to evaluate the potential efficacy of new therapies.
3.3.1 Chemical induced
model
Both small animals (e.g. mice and rats), or large animals (e.g. dogs,
sheep and pig) can be used to as toxic DCM model induced by
intracoronary adriamycin or isoprenaline. These chemical agents can
produce dose-dependent dilated phenotype associated with arrhythmias,
myocyte loss, and fibrosis, with progression to heart failure. Sheep
undergo sequential intracoronary injections of adriamycin causing a
dilated phenotype with dramatically reduced EF and increased LV volumes,
resulting in decrease of LV wall thickness and eventually in HF
(Borenstein et al., 2006). These models are particularly attractive as
it easy to perform in common laboratories without the need of surgical
procedures. However, the disadvantages of these methods are also
obvious, including the variability of response to doxorubicin, the
degree of LV dysfunction, animal mortality caused by arrhythmia, and
engenders several systemic side effects, such as bone marrow
suppression, gastrointestinal discomfort.
3.3.2 Rapid ventricular pacing
model
DCM induced by persistent and inappropriate tachycardia can be simulated
by rapid ventricular pacing model, which is commonly applied to large
animal studies, mostly in the canine model (Byrne et al., 2002; Shannon,
Komamura, Shen, Bishop, & Vatner, 1993; Spinale et al., 1997; Takagaki
et al., 2002). Rapid pacing can be performed by pacing leads implanted
in the atrium, right atrium or left atrium, to lead to a rapid and
significant decline in cardiac function, thus meeting the hemodynamic
conditions of HF. The severity of cardiac dysfunction depends on the two
factors: pacing rate and duration, of which the pacing rate is
controlled by programmable internal or external pacemakers in the range
of 200-300 bpm according to specific conditions, while the duration of
pacing varies from a few days to several weeks (Y.-T. Shen et al.,
2017). This model can cause high output HF, accompanied by biventricular
dilatation, a deterioration of systolic and diastolic function and
activation of neurohormone axis. Along with progressive HF, plasma
catecholamine levels increase. At more advanced stages, the levels of
endothelin and renin increased and the density of β receptor decreased,
all of which closely resembling the phenotype of CHF in human. However,
a major drawback of rapid ventricular pacing model is that the
cardiovascular hemodynamics and biochemical alterations would
progressively revert to near baseline levels after pacing stopped (Byrne
et al., 2002).
3.3.3 Transgenic animal
models
In small animals, two mouse strains were established in rodents to
simulate the development, progression and regression of human DCM. A
muscle LIM protein (MLP)-/-mouse developed by the deletion of
actin-related cytoskeleton protein (Arber et al., 1997), which gradually
decreases heart function from 4 to 6 months after birth and continues to
develop into dilated cardiomyopathy with hypertrophy and HF. The other
is calcium binding protein calsequestring (CSQ) mice produced by
cardiac-restricted overexpression of the CQS in the (Sato et al., 1998)
heart. By echocardiography, CSQ mice showed mild LV enlargement at 7
weeks, and mild decreased fractional shortening with increased wall
thickness. At age of 14 weeks, the phenotype developed into obvious LV
enlargement and severe systolic function decline (Cho et al., 1999). In
addition, these two mouse strains replicate other aspects of human
dilated cardiomyopathy, including abnormal β -adrenergic receptor (β-AR)
signal transduction.
3.4 HF induced by dilated
cardiomyopathy
Typical symptoms of HF, including shortness of breath, peripheral and
pulmonary edema, and low exercise tolerance, can be caused by two types
of valve lesions: aortic stenosis (AS) (abnormally high ejection
resistance prevents the valve from fully opening) or mitral
regurgitation (MR) (a failure of complete coaptation of the leaflets and
adequate closure) (Houser et al., 2012). Although these two types of
valve disease will eventually lead to HF events such as LV
diastolic/atrial pressure, fluid retention and fatigue, they have
different underlying pathophysiological characteristics. The former can
lead to significant LV pressure overload, whereas the latter causes a
significant LV volume overload.
3.4.1 Transverse aortic
constriction
In small animals, the most widely used model of aortic stenosis is the
Transverse aortic constriction (TAC), which is characterized by an
initial compensatory phase with concentric LV hypertrophy, followed by
enlargement of the cardiac chamber with further deterioration of LV
function, and eventually leading to HF. These characteristics are
similar to the progression of human HF, particularly in patients with
aortic stenosis. Therefore, TAC is often used to induce chronic LV
pressure overload and hypertrophy in rodents (Boluyt et al., 2005; Li et
al., 2012; Litwin et al., 1995). Several TAC surgical techniques have
been developed, including a minimally invasive approach by making a
small incision in the proximal sternum, and placement of surgical clips,
sutures, or O-rings to prevent blood flow through the aortic arch
(Riehle & Bauersachs, 2019). Besides
constriction at TAC, the surgical
constriction can also be performed at other locations, including
ascending aortic constriction (AAC), or abdominal aorta. These models
result in varied effects depending on the anatomic location of the
constriction, in general, constriction at AAC is used to study the
effects of early injury due to pressure overload, while TAC and
suprarenal aortic coarctation appear as more gradual increases in
pressure leading to hypertrophy and HF (Gomes et al., 2013). Moreover,
factors that affect the hypertrophy response and progression in HF
include sex, body weight, age, and genetic background of the species
used (Barrick, Rojas, Schoonhoven, Smyth, & Threadgill, 2007). Several
studies have also described in large animal models with progressive
aortic contraction on supravalvular position (Moorjani et al., 2006;
Tagawa et al., 1998; Ye, Gong, Ochiai, Liu, & Zhang, 2001). These
animal models replicate many key characteristics of human aortic
stenosis, including the gradual increase of LV aortic pressure gradient
and compensatory LV remodeling reaction, accompanied by myocardial
hypertrophy, cellular hypertrophy with evidence of diastolic HF and
abnormal myocardial matrix. The shortcomings of TAC model are that they
do not possess some of the key features of human disease, including the
inability to easily induce slowly progressive stress overload, and other
limitations include the long duration of the experimental protocol,
variability in the individual response to stress overload, and a
reduction in the high proportion of constriction due to internalization
of the contractile knot.
3.4.2 Chordae tendineae
cutting
Mitral valve insufficiency leads to chronic volume overload, resulting
in compensatory LV hypertrophy, followed by dilatation with pulmonary
edema. In large animals (most commonly the dog or sheep), significant
clinical phenotype of chronic mitral regurgitation can be induced by
cutting chordae tendineae (Leroux, Moonen, Pierard, Kolh, & Amory,
2012; Nielsen et al., 2003). MR occurs in canine model leads to LV
dilatation and eccentric LVH pattern, which is accompanied by the
increase of muscle cell length, the change of myofilament structure and
the decrease of myofibril content. Different from LVH in large AS animal
model, chronic MR in dogs can lead to severe LV contractile dysfunction
at both levels of chamber and myocyte (Spinale et al., 1993). This
chronic MR model has been successfully used to test the role of
angiotensin II receptor pathways in the progression of HF (Perry et al.,
2002). Although the use of angiotensin II type-1 (AT1) receptor blocker
(AT1RB) in this study reduced systemic vascular
resistance and local expression of the renin-angiotensin system in the
MR dog model, it did not prevent adverse left ventricular and myocardial
cell remodeling in the early myocardial adaptive phase of MR.
To date, there is no universally accepted model for MR in small animals.
Some such attempts have been made by Min et al. (Kim et al., 2012), who
develop a rat MR model by inserted a fine needle (0.36 mm in diameter)
into LV through the apex of LV, followed by pushing a needle into the
mitral valve to puncture and/or tear the mitral leaflets to form MR. In
this model, the time course of LV remodeling and functional change is
similar to that of human. Since this MR model was created by perforating
the mitral leaflet, it does not represent MR in human, particularly
ischemic MR, which is an inherent limitation of animal models of
valvular disease. However, it can still be used as an inexpensive model
for evaluating the effects of drug therapy on MR-induced LV remodeling,
which is important for clinical translational research.