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ORIGINAL ARTICLE
Factor Xa Inhibition with Apixaban Does Not Influence Cardiac
Remodelling in Rats with Heart Failure After Myocardial Infarction
Salva R. Yurista
1
&Herman H. W. Silljé
1
&Kirsten T. Nijholt
1
&Martin M. Dokter
1
&Dirk J. van Veldhuisen
1
&
Rudolf A. de Boer
1
&B. Daan Westenbrink
1
#The Author(s) 2020
Abstract
Background Heart failure (HF) is considered to be a prothrombotic condition and it has been suggested that coagulation factors
contribute to maladaptive cardiac remodelling via activation of the protease-activated receptor 1 (PAR1). We tested the hypoth-
esis that anticoagulation with the factor Xa (FXa) inhibitor apixaban would ameliorate cardiac remodelling in rats with HF after
myocardial infarction (MI).
Methods and Results Male Sprague-Dawley rats were either subjected to permanent ligation of the left ascending coronary artery
(MI) or sham surgery. The MI and sham animals were randomly allocated to treatment with placebo or apixaban in the chow
(150 mg/kg/day), starting 2 weeks after surgery. Cardiac function was assessed using echocardiography and histological and
molecular markers of cardiac hypertrophy were assessed in the left ventricle (LV). Apixaban resulted in a fivefold increase in
anti-FXa activity compared with vehicle, but no overt bleeding was observed and haematocrit levels remained similar in
apixaban- and vehicle-treated groups. After 10 weeks of treatment, LV ejection fraction was 42 ± 3% in the MI group treated
with apixaban and 37 ± 2 in the vehicle-treated MI group (p> 0.05). Both vehicle- and apixaban-treated MI groups also displayed
similar degrees of LV dilatation, LV hypertrophy and interstitial fibrosis. Histological and molecular markers for pathological
remodelling were also comparable between groups, as was the activity of signalling pathways downstream of the PAR1 receptor.
Conclusion FXa inhibition with apixaban does notinfluence pathological cardiac remodelling after MI. These datado not support
the use of FXa inhibitor in HF patients with the aim to amend the severity of HF.
Keywords Anticoagulant .Heart failure .Cardiac function .Cardiac remodelling
Introduction
Heart failure is a major global health problem that is reaching
epidemic proportions in the near future [1,2]. Despite the large
range of pharmacological and device-based therapies available,
mortality and morbidity remain high [3]. Patients with heart fail-
ure (HF) are at increased risk of stroke and other thromboembolic
events and are also more likely to succumb from these events
[4–9]. The higher incidence of thromboembolic events is ob-
served both in patients with sinus rhythm with atrial fibrillation
[10,11], suggesting that HF should be considered as a
prothrombotic or hypercoagulable state. Interestingly, coagula-
tion factors such as thrombin and FXa can exert direct effects on
the heart, which are thought to promote inflammation, endothe-
lial dysfunction and maladaptive cardiac remodelling [12].
Anticoagulants could therefore offer therapeutic benefits in HF
patients beyond the prevention of thromboembolic events [10].
The effects of thrombin and FXa on myocardial tissues are
thoughttobegovernedbyprotease-activatedreceptors
(PARs), which coordinate a myriad of cellular responses in
multiple cell types. PAR1 and PAR2 are expressed in cardiac
tissue and it has been proposed that these receptors contribute
to the progression of HF [13–15]. Indeed, cardiomyocyte-
specific overexpression of PAR1 induces cardiac hypertrophy
Electronic supplementary material The online version of this article
(https://doi.org/10.1007/s10557-020-06999-7) contains supplementary
material, which is available to authorized users.
*B. Daan Westenbrink
b.d.westenbrink@umcg.nl
1
Department of Cardiology, University Medical Center Groningen,
University of Groningen, PO Box 30.001, Groningen 9700 RB,
The Netherlands
https://doi.org/10.1007/s10557-020-06999-7
Published online: 26 May 2020
Cardiovascular Drugs and Therapy (2021) 35:953–963
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
that rapidly progressed into dilated cardiomyopathy [16].
Conversely, deletion of the PAR1 receptor attenuates cardiac
remodelling after a myocardial infarction (MI) in mice [16].
Nevertheless, direct evidence for enhanced activity of PARs
in HF is sparse and the exact role of PAR signalling in cardiac
remodelling remains poorly defined. Furthermore, it is un-
known whether PAR receptor activation in HF is amendable
by anticoagulant therapy. In this study, we tested the hypoth-
esis that inhibition of PAR signalling by the direct FXa inhib-
itor apixaban could attenuate cardiac remodelling in rats with
established LV dysfunction after MI.
Methods
Experimental Protocol
Male Sprague-Dawley rats (Envigo, The Netherlands) were
randomized to treatment with chow containing apixaban or
control chow, starting 2 weeks after MI surgery. We chose
this protocol to represent a population of stable chronic HF
after a large myocardial infarction, which still represents the
majority of patients with chronic HF. Here, we examined the
effects of clinically relevant doses of apixaban on cardiac re-
modelling in rats with HF after MI [17]. Treatment allocation
was stratified according to left ventricular ejection fraction
(LVEF) to ensure that the baseline cardiac function is similar
in the apixaban and the vehicle groups. After 10 weeks of
treatment, rats were anaesthetized, blood was drawn and the
hearts were rapidly excised for further analysis. Rats with an
infarct size of less than 15% were excluded from analysis as
these small infarcts are haemodynamically fully compensated
[18]. The experimental protocol is illustrated in Scheme 1.
Ethical Statement
The experimental protocol was approved by the Animal Ethical
Committee of the University of Groningen (IvD number: 16487-
02-001). The investigation conforms to the Guide for the Care
and Use of Laboratory Animals published by the US National
Institutes of Health (NIH publication no. 85–23, revised 1996).
We followed ARRIVE guidelines when reporting this study.
MI Surgery
Rats were randomized to HF or sham surgery under isoflurane
(2.5%) inhalation anaesthesia. After left-sided thoracotomy,
HF was induced by permanent ligating of the proximal portion
of the left coronary artery as previously described [19]. Sham-
operated rats underwent the same procedure but without cor-
onary ligation.
Investigational Drug
Apixaban was kindly supplied by Bristol-Myers Squibb
(BMS), USA. Apixaban was mixed with standard rat chow
(R/M-H V1534-70, Ssniff, Germany) in a final concentration
of 1.95 g/kg intended to reach an average dose of 150 mg/kg.
Standard rat chow (R/M-H V1534-70, Ssniff, Germany) was
used as the control (vehicle).
Echocardiography
Two weeks after surgery and 1 week before termination, the
M-mode and 2D echocardiography were performed using a
Vivid 7 echo machine (GE Healthcare) equipped with a 10-
MHz phase array linear transducer for serial assessment of
cardiac structure and function as previously described [19].
Invasive Haemodyamic Measurements
Prior to sacrifice, invasive haemodynamics were analysed by
aortic and LV catheterization as previously described [19]. The
right carotid artery was isolated and punctured and a 1.9-F rat
pressure-volume catheter (Scisense, London, Ontario, Canada)
was inserted into the right carotid artery. The tip of the catheter
was advanced through the aorta into the LV cavity. Heart rate
(HR), left ventricular end-systolic (LVESP) and end-diastolic
(LVEDP) pressures, and maximal rates of increase and decrease
in developed LV pressure (dP/dtmax and dP/dtmin) were deter-
mined. The data were acquired using a PowerLab data acquisi-
tion system (ADInstruments, Colorado Springs, CO) and
analysed with a LabChart 8 software.
2 weeks
MI / sham
Surgery Echo Echo
11 weeks 12 weeks0
Male Sprague-
Dawley rats
Sacrifice
Scheme 1 Schematic representation of the experimental protocol
954 Cardiovasc Drugs Ther (2021) 35:953–963
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Infarct Size, Cardiomyocyte Size and Interstitial
Fibrosis Measurement
Rats were euthanized under isoflurane anaesthesia. The heart
was rapidly excised and weighed. The mid-papillary slice of
the LV was fixed in 4% formaldehyde and paraffin-embed-
ded. The infarct size was calculated using midline length
methods as the percentage of the scar length to the total LV
circumference on Masson’strichrome–stained section, as de-
scribed previously [19,20]. Furthermore, Masson’strichrome
staining was also used to evaluate the extent of interstitial
fibrosis. A Hamamatsu microscope was used to capture the
whole tissue section and an Aperio ImageScope software was
used to quantify fibrosis in the non-infarcted LV [19]. Finally,
sections were stained with FITC-labelled wheat germ agglu-
tinin (WGA) to determine cardiomyocyte size as previously
described [19]. Cell size from transversally cut
cardiomyocytes in the non-infarcted LV was measured using
an image analyser (Zeiss KS400, Germany) and a quantified
using ImageJ software (National Institutes of Health,
Bethesda, MD, USA). The investigators analysing the data
were blinded to the treatment allocation.
Blood and Urine Measurements
Blood samples were obtained via a tail vein under isoflurane
anaesthesia to determine anti-factor Xa activity (AXA), pro-
thrombin time (PT) and activated partial thromboplastin time
(APTT) levels. At sacrifice, 8 ml of blood was drawn from the
abdominal aorta (either anti-coagulated with sodium citrate or
EDTA), and urine was collected directly from the bladder.
Complete blood count was determined on the day of sacrifice
using a Sysmex Hematology Analyzer (Symex XN-10,
Sysmex Corporation, Japan).
Prothrombin Time, Activated Partial Thromboplastin
Time and Anti-Factor Xa Activity Assay
To determine the effect of apixaban on PT and APTT levels,
each sample was tested using Innovin (PT) and Actin FS
(APTT) reagents (Siemens Healthcare Diagnostics). Plasma
apixaban concentration was assessed using a chromogenic
anti-factor Xa activity (AXA) assay, the Berichrom Heparin
Assay (Dade Behring, Marburg, Germany) as this is the most
reliable method to measure the pharmacodynamics of
apixaban [21].
Urine Occult Blood Test
Haemoglobin/red blood cells were determined by a semiquan-
titative method using Combur10 Test Sticks (Roche
Diagnostics GmbH, Mannheim, Germany).
Quantitative Real-time PCR
RNA was extracted from the non-infarcted LV using TRIzol
reagent (Invitrogen Corp., Carlsbad, CA, USA), as previously
described [19,22] and the NanoDrop device was used to mea-
sure RNA concentration. Random primer mix was used to
prepare first-stranded DNA and thereafter used as a template
for quantitative real-time reverse-transcriptase PCR (qRT-
PCR) (25 ng/reaction). mRNA levels obtained by a qRT-
PCR using a C1000 Thermal Cycler CFX384 Real-Time
PCR Detection System (Bio-Rad Laboratories, Veenendaal,
The Netherlands). 36B4 reference gene was used to correct all
measured mRNA expression. Primer sequences can be found
in Supplementary table S1.
Western Blot
Frozen non-infarcted LV tissue was homogenized in ice-cold
lysis buffer containing phosphatase inhibitor cocktail 1
(Sigma) and protease inhibitor (ROCHE) as described previ-
ously [19]. Bio-Rad DC Protein Assay (Bio-Rad Laboratories,
Veenendaal, The Netherlands) was used for protein quantifi-
cations with bovine albumin as a standard, as described before
[19]. Immunoblotting was performed using primary antibod-
ies from commercial suppliers (Supplementary table S2).
Immunoblots were incubated with appropriate secondary an-
tibodies for 1 h at room temperature. Signals were detected by
ECL (ParkinElmer, Waltham, MA, USA). Blots were quanti-
fied using ImageJ software (National Institutes of Health,
Bethesda, MD, USA). The density of each band was normal-
ized to GADPH acting as a loading control and presented as
fold change over Sham-veh group.
RhoA Activity Assay
RhoA activity was measured according to the manufacturer’s
protocol (BK124; Cytoskeleton Inc.), as previously described
[23].
Statistical Analysis
Data are presented as means ± standard errors of the mean
(SEM). To compare normally distributed parameters, one-
way analysis of variance (ANOVA) followed by Tukey’spost
hoc test was used. When data were not normally distributed, a
non-parametric Kruskal-Wallis test followed by a Mann-
Whitney Utest with correction for multiple comparisons
was used. Wilcoxon signed-rank test was used to evaluate
LVEF post-MI vs before termination. Differences were con-
sidered significant at p< 0.05. IBM SPSS Statistics for
Windows, Version 23.0 (IBM Corp, USA), was used to per-
form all statistical analysis.
955Cardiovasc Drugs Ther (2021) 35:953–963
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Results
We performed MI or sham surgery on a total of 78 male
Sprague-Dawley rats; 21 rats (27%) died during the surgical
procedure; all remaining rats survived the rest of the study. A
total of 4 rats with an infarct < 15% of the LV were excluded
from further analysis, leaving a total of 53 rats for the analysis.
The final group sizes were 8 for the sham-apixaban group, 13
for the sham-vehicle group, 17 for the MI-apixaban group and
15 for the MI-vehicle group.
Efficacy and Safety of Apixaban in Rats with HF After
MI
Efficacy of Apixaban
Daily food intake and water intake were comparable among the
groups (Table 1). As expected, plasma PT and APTT were not
affected by apixaban treatment (Table 1)[24]. In rats treated with
apixaban, the plasma AXA activity was increased by fivefold as
compared with that in vehicle-treated rats (Table 1).
Safety of Apixaban
We did not observe any bleeding events during the study, nor
did we observe reductions in haemoglobin levels (Table 1)or
detect blood in the urine (Supplementary fig. S1).
Furthermore, apixaban did not affect other haematological
parameters such as white blood cells (WBC), red blood cells
(RBC), haematocrit (HCT) and platelet (PLT) counts
(Table 1). Body weight was similar in apixaban- and
vehicle-treated groups (Table 1).
Effect of Apixaban on Cardiac Function
The average MI size was 38 ± 2% and was comparable be-
tween MI-vehicle and MI-apixaban (Fig. 1a, b). MI surgery
resulted in cardiac dilatation and a marked reduction in LVEF
(Fig. 1b, c). At the initiation of therapy, 2 weeks after MI, all
indices of left ventricular function were comparable between
the MI-Apixaban and the MI-vehicle groups. As expected, a
progressive deterioration in LVEF was observed in the MI-
vehicle group over the 10-week treatment period (Fig. 1e).
Treatment with apixaban did not alter cardiac function and
all echocardiographic parameters remained comparable be-
tween the MI-vehicle- and the MI-apixaban-treated animals
(Fig. 1, Table 2). All other relevant echocardiographic param-
eters at week 11 are depicted in Table 2. The infarcted rats
were haemodynamically compromised, as reflected by a de-
crease in contractility and relaxation (dP/dt max-min), and an
increase in LVEDP. Treatment with apixaban did not alter
these parameters (Table 3). Moreover, no significant differ-
ence was found in systolic blood pressure or diastolic blood
pressure among the groups (Table 3).
Effect of Apixaban on Cardiac Histology and
Molecular Markers for Remodelling and Fibrosis
The biventricular weight/tibia lengths ratio was calculated as a
marker of hypertrophy and was found to be significantly
Table 1 General characteristics
and haematological parameters Parameters Sham-vehicle Sham-
apixaban
MI-vehicle MI-apixaban
Food intake (g/day) 31.9 ± 0.5 29.9 ± 0.7 30.3 ± 0.5 29.6 ± 0.3
Water intake (ml/day) 32.0 ± 0.9 29.9 ± 0.6 30.9 ± 1.0 28.5 ± 0.4
Body weight change (g) 91.15 ± 3.2 93.25 ± 4.8 94.73 ± 4.8 93.24 ± 4.8
AXA (ng/ml) 21 ± 2 109 ± 17
†
19 ± 1 103 ± 11
#
PT (s) 11.12 ± 0.12 11.00 ± 0.10 11.31 ± 0.21 11.17 ± 0.17
APTT (s) 15.48 ± 1.13 16.74 ± 0.62 17.24 ± 1.20 16.91 ± 0.94
WBC (10^9/l) 9.34 ± 2.18 11.34 ± 0.68 11.23 ± 1.24 10.66 ± 0.80
RBC (10^12/l) 9.01 ± 0.17 8.94 ± 0.10 8.99 ± 0.10 9.32 ± 0.23
HCT (mmol/l) 10.02 ± 0.25 9.84 ± 0.12 9.79 ± 0.13 10.00 ± 0.12
HGB (l/l) 0.503 ± 0.02 0.489 ± 0.01 0.493 ± 0.01 0.505 ± 0.01
PLT (10^9/l) 1025.60 ± 53.50 911.00 ± 47.85 826.56 ± 57.10 946.50 ± 57.56
Data are presented as means ± SEM
†
p< 0.05 vs Sham-veh
#
p<0.05vsMI-veh
AXA, anti-factor Xa activity; PT, prothrombin time; APTT, activated partial thromboplastin time; WBC, white
blood cell count; RBC, red blood cell count; HCT, haematocrit; HGB: haemoglobin; PLT, absolute automated
platelet count
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Post-MI Before termination
0
30
40
50
60
70
Ejection fraction (%)
MI-Vehicle
MI-Apixaban
VehApixVehApix
0
25
30
35
40
Biventricular weight / TL
(mg/mm)
Sham MI
*
*
Ejection fraction (%)
Veh Apix Veh Apix
0
20
40
60
80
Sham MI
*
*
Veh Apix Veh Apix
0
6
8
10
LVIDd (mm)
Sham MI
*
*
Infarct size (%)
Veh Apix Veh Apix
0
10
20
30
40
50
Sham
MI
Sham-Vehicle Sham-Apixaban MI-Vehicle MI-Apixaban
Masson trichrome
a
cdb
ef
Fig. 1 Effect of apixaban on cardiac function. aRepresentative LV
sections stained with Masson’s trichrome. bQuantification of infarct
size from Masson’s trichrome–stained section; n=8–17/group. cLeft
ventricular internal dimensions in diastole (LVIDd) at week 11; n=8–
17/group.dEjection fraction of the LV at week 11. eLongitudinal change
of LV ejection fraction post-MI and before termination; n=8–17/group. f
Ratio of biventricular weight to tibia length; n=8–17/group. Data are
presented as means ± SEM. *p< 0.05 vs sham with the same treatment;
‡
p<0.05vsMI—post-MI
Table 2 Echocardiography
parameters in sham-operated and
post-myocardial infarction rats at
week 11
Sham-veh Sham-
apixaban
MI-vehicle MI-apixaban
IVSd (mm) 2.09 ± 0.15 2.46 ± 0.13 1.89 ± 0.10* 1.81 ± 0.13*
LVIDd (mm) 7.67 ± 0.22 7.34 ± 0.18 9.29 ± 0.31* 8.99 ± 0.33*
LVPWd (mm) 2.18± 0.13 2.23 ± 0.27 1.88 ± 0.12 1.85 ± 0.12
IVSs (mm) 3.45 ± 0.18 3.64 ± 0.27 2.39 ± 0.15* 2.31 ± 0.21*
LVIDs (mm) 4.52 ± 0.25 4.38 ± 0.22 7.52 ± 0.37* 7.04 ± 0.35*
LVPWs (mm) 3.14 ± 0.13 2.86 ± 0.34 2.37 ± 0.10* 2.42 ± 0.14
FS (%) 41.41 ± 2.37 37.40 ± 1.68 19.02 ± 1.22* 22.17 ± 1.76*
EF (%) 70 ± 2 66 ± 2 37 ± 2* 42 ± 3*
Data are presented as means ± SEM
*p< 0.05 vs sham with the same treatment
IVS, interventricular in diastole (d) and systole (s), respectively; LVID, left ventricular internal dimensions in both
diastole (d) and systole (s); LVPW, the thickness of left ventricle posterior wall in diastole (d) and systole (s); FS,
fractional shortening; EF, left ventricular ejection fraction
957Cardiovasc Drugs Ther (2021) 35:953–963
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increased in MI-vehicle rats compared with that in sham-
operated rats (Fig. 1e).TheMIratsdemonstratedincreased
cardiomyocyte cross-sectional area and fibrosis compared
with the control rats (Fig. 2a–c). However, apixaban therapy
did not affect the extent of cardiac hypertrophy nor did it
influence the degree of LV fibrosis (Fig. 2a–c).
MI surgery increased the myocardial expression of atrial
natriuretic peptide (ANP), and brain natriuretic peptide (BNP)
and increased the relative expression of foetal (β-MHC) com-
pared to with that of adult (α-MHC)myosinheavychainiso-
form (i.e. β-MHC/α-MHC ratio), as markers for foetal gene
reprogramming in heart failure (Fig. 2d). The mRNA levels of
cardiac fibrosis markers collagen, type I, alpha 1 (COL1A1)
and tissue inhibitor of metalloproteinases 1 (TIMP1) were also
significantly increased in the hearts of rats following MI, com-
pared to with that in the hearts of sham rats (Fig. 2e). Apixaban
treatment had no effect on ANP, BNP, β-MHC/α-MHC ratio,
COL1A1 or TIMP1 mRNA levels (Fig. 2d, e).
Effect of Apixaban on PAR1 Signalling Pathways
Next, we aimed to determine whether apixaban influenced the
activity of thrombin-related pathways downstream of the
PAR1 receptor. Binding of thrombin to the PAR1 receptor
results in the activation of RhoA, which in turn phosphory-
lates Rho-associated coiled-coil kinase (ROCK) [25]. The
RhoA/ROCK pathway has been shown to contribute to cardi-
ac remodelling in HF [26,27] It has also been reported that
PAR1 activates AKT and ERK, two well-established regula-
tors of cardiac remodelling, independent from RhoA [16,28].
Next, we determined the effects of Apixaban on myocardi-
al RhoA activity. As expected, RhoA activity was increased
after MI, but the RhoA activity did not differ between the MI-
vehicle and the MI-apixaban group (Fig. 3a). Furthermore,
apixaban did not influence the phosphorylation levels of
AKT (Fig. 3b, d), nor did it affect the activation of ERK1/2
(data not shown). Finally, the LV protein expression levels of
the PAR1 receptor were comparable between all groups
(Fig. 3b, c), indicating that the results above could not be
explained by aberrant expression of the PAR1 receptor.
Discussion
We tested the hypothesis that treatment with FXa inhibitors
apixaban would improve cardiac function and ameliorate car-
diac remodelling in rats with HF after a large transmural an-
terior MI. For this purpose, we used a well-established model
of chronic post-MI HF and ensured that the degree of LV
dysfunction was similar in the apixaban and vehicle-treated
groups at the initiation of therapy. Furthermore, we used a
clinically relevant dose of apixaban that also appeared to be
safe and effective, as evidenced by a consistent 5-fold increase
in AXA and by the absence of (occult) bleeding. We demon-
strate that treatment with apixaban did not influence LV func-
tion, nor did it influence LV dilatation of LV hypertrophy.
Moreover, histological and molecular markers for pathologi-
cal LV remodelling were also not influenced by apixaban and
the activity of signal transduction pathways downstream of
the PAR1 was unaltered. These findings suggest that the in-
hibition of FXa with a safe, effective and clinically relevant
dose of apixaban does not influence cardiac remodelling in the
chronic phase after MI. In addition, our findings suggest that
the role of thrombin-mediated PAR1 receptor activation to the
pathophysiology of HF is limited. Our findings are in line with
the results from the COMMANDER HF trial and do not sup-
port the use of FXa inhibitor in HF patients with the aim to
amend the severity of HF.
HF reflects a pro-coagulant state, because all prerequisites
for thrombosis as described in Virchow’s law are met:
Table 3 Haemodynamic
parameters in sham-operated and
post-myocardial infarction rats
Sham-veh Sham-
apixaban
MI-vehicle MI-apixaban
HR (bpm) 287 ± 15 291 ± 13 299 ± 11 291 ± 8
SBP (mmHg) 119.24 ± 4.37 115.87 ± 6.01 115.77 ± 3.25 110.42 ± 1.93
DBP (mmHg) 84.69 ± 3.45 73.63 ± 2.36 82.66 ± 2.19 75.31 ± 2.46
LVESP (mmHg) 104.49 ± 8.30 110.77 ± 5.78 110.35 ± 3.17 105.94 ± 3.45
LVEDP (mmHg) 12.10 ± 2.24 11.40 ± 1.02 16.30 ± 0.80* 15.85 ± 0.76*
dP/dt max (mmHg/s) 6848 ± 239 6432 ± 504 5427 ± 173* 5021 ± 297*
dP/dt min (mmHg/s) −7683 ± 302 −6766 ± 456 −5285 ± 224* −5304 ± 250*
Data are presented as means ± SEM
*p< 0.05 vs sham with the same treatment
HR, heart rate; bpm, beat per minute; SBP, systolic blood pressure; DBP, diastolic blood pressure; LVESP, left
ventricular end-systolic pressure; LVEDP, left ventricular end-diastolic pressure; dP/dtmax and dP/dtmin,the
maximal rate of increase and decrease of left ventricular pressure, respectively
958 Cardiovasc Drugs Ther (2021) 35:953–963
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0
1
2
3
4
5
mRNA level (fold change)
Vehicle
Apixaban
Sham Sham ShamMI MI MI
*
*
*
***
0.0
0.5
1.0
1.5
2.0
2.5
mRNA level (fold change)
Vehicle
Apixaban
Sham ShamMI MI
*
**
*
% Fibrosis
Veh Apix Veh Apix
0
5
10
15
20
25
Sham MI
*
*
Cardiomyocyte CSA (µm2)
Veh Apix Veh Apix
0
200
400
600
800
1000
Sham MI
*
*
ab
cd e
Fig. 2 Effect of apixaban on cardiac histology and molecular markers for
remodelling and fibrosis. aQuantification of cardiomyocyte cross-
sectional area from WGA-stained section; n=8–17/group. b
Representative LV sections stained with WGA and Masson’strichrome
to assess cardiomyocyte hypertrophy and fibrosis. cQuantification of
fibrosis in non-infarcted LV from Masson’strichrome–stained section;
n=8–17/group. d,eMeasurement of mRNA levels to assess molecular
markers for remodelling and fibrosis in non-infarcted LV, respectively,
normalized to 36b4; n=8–17/group. Data are presented as means ± SEM.
*p< 0.05 vs sham with the same treatment
RhoA activity (fold change)
Veh Apix Veh Apix
0.0
0.5
1.0
1.5
2.0
2.5
Sham MI
*
*
PAR1 relative expression
(fold change)
Veh Apix Veh Apix
0.0
0.5
1.0
1.5
Sham MI
pAKT/AKT relative
expression (fold change)
Veh Apix Veh Apix
0.0
0.5
1.0
1.5
Sham MI
PAR 1
pAKT
AKT
GAPDH
Sham-Veh Sham-Apix MI-Veh MI-Apix
ab
cd
Fig. 3 Effect of apixaban on
PAR1 signalling pathways. a
RhoA activity; n=6/group. b
Western blot analysis of PAR1,
total and phosphorylated Akt; n=
6/group. cQuantification of
PAR1 protein levels; n=6/group.
dQuantification of Akt
phosphorylation protein levels;
n= 6/group. Apix, apixaban. The
density of each band was
normalized to GADPH acting as a
loading control and presented as
fold change over Sham-veh
group. Data are presented as
means ± SEM. *p< 0.05 vs sham
with the same treatment
959Cardiovasc Drugs Ther (2021) 35:953–963
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abnormalities in blood flow, in the vessel wall and in blood
constituents [29,30]. Aberrant platelet activation and in-
creased levels of pro-coagulant factors reflect abnormalities
in blood constituents. Impaired contractility and dilated cham-
bers perturb myocardial blood flow and endothelial damage
and reduced endothelium-dependent vasodilation reflect the
changes in the vessel wall [31]. It has been previously recog-
nized that patients with HF have an increased risk of throm-
boembolic events, both systemic and venous. The
prothrombotic molecules, such as fibrinogen and von
Willebrand factors, have been found to be elevated in subjects
with HF. Moreover, previous studies showed that the throm-
botic risk associated with HF appears to increase with the
severity of the disease [32,33]. A large Danish prospective
cohort study demonstrated that the risk of stroke and throm-
boembolic event was increased in HF patients with HF inde-
pendent of the CHA2DS2-VASc score. Furthermore, in pa-
tients with HF and a CHA2DS2-VASc score ≥4, the absolute
risk of thromboembolic events was even higher in patients
without than with concomitant AF [34]. In addition, the prog-
nosis of HF markedly deteriorates after a thromboembolic
event occurs, suggesting that interventions to reduce throm-
boembolic events may improve prognosis in HF patients [35].
Another mechanism by which the hypercoagulable state could
contribute to the progression of HF is coronary microvascular
embolization leading to MI [36,37].
Anticoagulants are often prescribed in HF patients without
AF that are considered to be at high risk for stroke, such as
those with an LV thrombus. There is, however, very little
evidence to support the lenient prescription of anticoagulants
in patients with HF and sinus rhythm [38]. In the Warfarin
versus Aspirin in Reduced Cardiac Ejection Fraction
(WARCEF) trial, warfarin did not result in a meaningful re-
duction in the rates of ischaemic stroke, intracerebral haemor-
rhage or death from any cause [39]. Furthermore, the effect of
FXa inhibitor rivaroxaban on clinical outcomes was recently
tested in the COMMANDER HF (“A Study to Assess the
Effectiveness and Safety of Rivaroxaban in Reducing the
Risk of Death, Myocardial Infarction, or Stroke in
Participants with Heart Failure and Coronary Artery Disease
Following an Episode of Decompensated Heart Failure”)trial
[40]. The authors randomized > 5000 patients with chronic
ischaemic HF with reduced ejection fraction but without atrial
fibrillation to a low dose of rivaroxaban or placebo.
Rivaroxaban was safe and well tolerated, but did not affect
the incidence of the combined endpoint of all-cause mortality,
stroke or myocardial infarction. In both the WARCEF and the
COMMANDER HF study, anticoagulation did reduce the in-
cidence of ischaemic stroke, suggesting that the lack of effect
was not dose related. Our results confirm and extend upon the
results of the COMMANDER HF trial and provide mechanis-
tic underpinnings that explain the neutral outcomes.
Furthermore, our findings suggest that clinically relevant
doses of FXa inhibitors do not influence PAR mediated sig-
nalling and cardiac remodelling.
To the best of our knowledge, our study is the first to study
the effect of Xa inhibition on cardiac remodelling in rats with
established LV dysfunction. Several studies have, however,
evaluated the early effect of FXa inhibition on myocardial
ischaemia/reperfusion injury and post-infarct remodelling.
The indirect FXa inhibitor fondaparinux has been shown to
reduceinfarctsizefollowing2hofreperfusioninaratmodel
of myocardial ischaemia-reperfusion [41]. The effects of FXa
inhibitors are more variable as Flierl et al. did not observe
infarct size reduction when rivaroxaban was given in rats with
permanent coronary ligation [42]. However, a similar study by
Bode et al. indicated that the administration of rivaroxaban
immediately after surgery resulted ina reduction in infarct size
and improvements in cardiac function. Conversely, when
rivaroxaban was initiated 3 days after MI surgery, no effect
on infarct size or cardiac function was observed [43]. Taken
together, the available evidence on the effect of FXa inhibitors
on cardiac function is in line with our observations and dis-
putes their utility in chronic HF setting.
There are four PAR isoforms, but PAR1 and PAR2 are the
predominant isoforms in the heart [13,16]. PAR1 is activated
by thrombin and FXa, but PAR2 is only activated by FXa.
Both receptors are expressed in cardiomyocytes and cardiac
fibroblast. Cleavage of PARs results in activation of several G
protein–coupled receptors and their downstream signalling
pathways, including RhoA/ROCK, the MAPK pathways,
ERK 1/2 and ERK5 [16]. Several lines of evidence indicate
that PARs are activated in HF and contribute to disease pro-
gression. First, PAR1 expression and the activity of its down-
stream signal transduction pathways are increased in murine
models of chronic HF and in the ventricles of HF patients with
ischaemic or idiopathic dilated cardiomyopathy [14,15].
Second, the activation of PARs in cultured cardiomyocytes
induces pathological hypertrophy, reflected by increases in
cell size and sarcomeric organization, the activation of the
foetal gene program and perturbations in cardiac calcium han-
dling [28]. Third, PAR1 activation in cardiac fibroblasts in-
duces a pro-fibrotic state reflected by enhanced proliferation
and increased expression of transforming growth factor Beta
(TGF-ß) [13,28,44]. Fourth, PAR1 activation is strongly pro-
inflammatory as it induces the expression of interleukin (IL)-
6, IL-8 and monocyte chemoattractant protein (MCP-1) [12,
13]. Yet, the most robust evidence comes from studies in
PAR1-knockout (KO) mice and mice with overexpressing
the PAR1. In a PAR1-KO mouse model, reduced cardiac re-
modelling was observed after I/R injury; however, infarct size
was not affected. Accordingly, mice with cardiomyocyte-
specific overexpression of PAR1 exhibited eccentric hypertro-
phy and dilated cardiomyopathy [16]. Additionally, PAR sig-
nalling activates RhoA/ROCK pathway [25,45] which has
been shown to mediate fibrosis in the heart [26]. Protein levels
960 Cardiovasc Drugs Ther (2021) 35:953–963
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
of ROCKs as well as RhoA activity were significantly in-
creased in CHF patients [27]. Furthermore, the deletion of
ROCK attenuates HF progression and improves the cardiac
performance in mice [46,47]. These findings provided a clear
rationale for our studies.
However, in contrast to our expectations, we did not ob-
serve any changes in protein levels for PAR1 protein, nor did
we detect differences in the activation of the AKT and ERK 1/
2 signal transduction pathways downstream of PAR1 [48].
These findings are in consistence with a previous study [49]
in which PAR1 protein expression did not differ at 12 weeks
after MI induction or apixaban treatment. Moreover, it has
been previously published that upregulated AKT exerts
cardioprotective effects in models of preconditioning resulting
in limiting infarct size [50,51]. However, AKT is not regulat-
ed in a chronic ischaemia setting [52], and this finding was
also seen in our study. Our observation that ERK1/2 protein
levels were also not affected in post-MI LV dysfunction is in
accordance with similar studies in post-MI LV dysfunction
[53]. Consistent with other reports, we were able to detect a
clear increase in RhoA activity after MI, but this was not
affected by treatment with apixaban.
Other studies have demonstrated evidence that FXa inhib-
itors can influence PAR receptor signalling. For instance,
Bukowska et al. showed that FXa inhibitor rivaroxaban re-
duced MAP kinase activity and diminished the upregulation
of PARs, ICAM-1, LOX-1 and IL-8 and in human atrial tissue
cultures in media containing activated FXa [54]. Interestingly,
FXa has also been shown to activate ERK1/2 and induce pro-
inflammatory cytokines in alveolar epithelial cells, which was
suppressed by FXa inhibitor edoxaban [55]. In addition, the
FXa inhibitor rivaroxaban did inhibit cardiac FXa activity and
reduced cardiac fibrosis in a model of transverse aortic con-
striction [56]. Our results may therefore have been different in
other disease models or if we would have induced a murine
model prone to develop cardiac thrombi [57].
Study Limitations
Despite strengths related to the direct measures of cardiac struc-
ture, function and other haematological parameters, our study
does have limitations. First, in accordance with the previous
study [49], we did not observe changes in PAR1 protein levels
in post-MI HF model. Furthermore, the activity of downstream
signalling pathways of the PAR1 was not increased after MI and
apixaban did not alter this. It is possible that the activation of
PAR1 and other thrombin-related pathways is more pronounced
in other models or settings. Second, we started the treatment
2 weeks after MI when infarct healing had completed; we cannot
exclude that FXa inhibition could be beneficial during earlier
stages of post-infarct remodelling. Third, we employed apixaban
at a dose that was within the safety range (FDA application no.
202155Orig1s000). Based on the AXA levels, this dosage is
comparable with a 5-mg dose in humans [17]. The outcome of
our study may have been different when a higher dose had been
used. The clinical relevance of a study with high-dose apixaban
is, however, limited as anticoagulants have a narrow therapeutic
window and the benefits are often offset by the associated in-
creased risk of bleeding events [39]. Our study does not exclude
the possibility that thrombin-related pathways and PARs contrib-
ute to cardiac remodelling in HF. Our findings do, however,
question the utility of FXa inhibitors as a pharmacological ther-
apy to attenuate cardiac remodelling. Importantly, our study is in
line with the neutral effects of the COMMANDER HF trial, and
the molecular insights do not hint towards a direct of effect of
apixaban on cardiac muscle structure and function.
Conclusions
FXa inhibition with apixaban does not influence pathological
cardiac remodelling after a MI. These data do not support the
use of FXa inhibitor in HF patients with the aim to amend the
severity of HF.
Clinical Perspectives
It has been suggested that coagulation factors such as factor
Xa (FXa) and thrombin promote maladaptive cardiac remod-
elling and could promote heart failure (HF) development via
activation of the protease-activated receptors (PARs) in myo-
cardial tissue. If this hypothesis is true, cardiac remodelling
would be amendable by treatment with anticoagulants. To test
this hypothesis, rats with HF after myocardial infarction (MI)
were treated with the FXa inhibitor apixaban or a matching
vehicle. While apixaban was effective in inhibiting FXa activ-
ity, it did not affect the activity of PAR1 signalling pathways,
nor did it affect cardiac function and cardiac remodelling after
MI. These findings are in line with the results of the recent
COMMANDER HF trial and do not support the use of FXa
inhibitors in HF patients with the aim to improve heart func-
tion or to modulate the clinical course of HF.
Acknowledgements We acknowledge Bristol-Myers Squibb for supply-
ing apixaban and thank Dr. William Achanzar for the support and expert
advice on determining the correct dosage for this study. We thank
Marloes Schouten, Janny Takens and Silke Oberdorf for the expert tech-
nical assistance and advice.
Authors’Contributions SRY, HHWS, RAdB and BDW designed the
research study. SRY and MMD performed the research. SRY and
BDW analysed the data. SRY and BDW wrote the paper. HHWS,
KTN, DJvV and RAdB revised the paper for important intellectual con-
tent. All authors read and approved the final manuscript.
961Cardiovasc Drugs Ther (2021) 35:953–963
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
Funding Information The study was funded by a competitive grant from
Bristol-Myers Squibb/Pfizer Alliance, within the European Thrombosis
Investigator-Initiated Research Program (ERISTA) (grant BMS ISR
#CV185-638).
Dr. Yurista is supported by a grant from the Indonesia Endowment
Fund for Education (LPDP no. 20150722083422). Dr. de Boer is sup-
ported by the Netherlands Heart Foundation (CVON DOSIS, grant 2014-
40; CVON SHE-PREDICTS-HF, grant 2017-21; and CVON RED-
CVD, grant 2017-11) and the Innovational Research Incentives Scheme
programme of the Netherlands Organization for Scientific Research
(NWO VIDI, grant 917.13.350). Dr. Westenbrink is supported by
The Netherlands Organisation for Scientific Research (NWO VENI,
grant 016.176.147).
Compliance and Ethical Standard
Ethics Approval and Consent to Participate The study was approved by
the University of Groningen Ethical Committee on Animal
Experimentation (IvD number: 16487-02-001). The investigation con-
forms to the Guide for the Care and Use of Laboratory Animals published
by the US National Institutes of Health and in accordance with national
regulations.
Competing Interests SRY, HHWS, KTN, MMD, DJvV and BDW do
not report conflicts of interest relative to this report. The UMCG, which
employs Dr. De Boer, has received research grants and/or fees from
AstraZeneca, Abbott, Bristol-Myers Squibb, Novartis, Roche, Trevena
and ThermoFisher GmbH. Dr. de Boer received personal fees from
MandalMed Inc., Novartis and Servier.
Disclaimer The funder had no role in the design and conduct of the
study; collection, management, analysis and interpretation of the data;
preparation, review or approval of the manuscript; and decision to submit
the manuscript for publication.
Open Access This article is licensed under a Creative Commons
Attribution 4.0 International License, which permits use, sharing,
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