Renal Damage after Myocardial Infarction Is Prevented by Renin-Angiotensin-Aldosterone-System Intervention

Renal Damage after Myocardial Infarction Is Prevented by
Renin-Angiotensin-Aldosterone-System Intervention
Willemijn A.K.M. Windt,* Wouter B.A. Eijkelkamp,* Robert H. Henning,*
Alex C.A. Kluppel,* Pieter A. de Graeff,* Hans L. Hillege,† Stefan Schäfer,‡
Dick de Zeeuw,* and Richard P.E. van Dokkum*
*Department of Clinical Pharmacology and †Department of Cardiology, Thorax Center, University Medical Center
Groningen, University of Groningen, Groningen, The Netherlands; and ‡Sanofi-Aventis Pharma Deutschland, Frankfurt
am Main, Germany
Recently, it was shown that myocardial infarction aggravates preexistent mild renal damage that is elicited by unilateral
nephrectomy in rats. The mechanism behind this cardiorenal interaction likely involves the renin-angiotensin-aldosteronesystem and/or vasoactive peptides that are metabolized by neutral endopeptidase (NEP). The renoprotective effect of
angiotensin-converting enzyme inhibition (ACEi) as well as combined ACE/NEP inhibition with a vasopeptidase inhibitor
(VPI) was investigated in the same model to clarify the underlying mechanism. At week 17 after sequential induction of
unilateral nephrectomy and myocardial infarction, treatment with lisinopril (ACEi), AVE7688 (VPI), or vehicle was initiated
for 6 wk. Proteinuria and systolic BP (SBP) were evaluated weekly. Renal damage was assessed primarily by proteinuria,
interstitial ␣-smooth muscle actin (␣-SMA) staining, and the incidence of focal glomerulosclerosis (FGS). At start of treatment,
proteinuria had increased progressively to 167 ⴞ 20 mg/d in the entire cohort (n ⴝ 42). Both ACEi and VPI provided a similar
reduction in proteinuria, ␣-SMA, and FGS compared with vehicle at week 23 (proteinuria 76 ⴞ 6 versus 77 ⴞ 4%; ␣-SMA 60 ⴞ
6 versus 77 ⴞ 3%; FGS 52 ⴞ 14 versus 61 ⴞ 10%). Similar reductions in systolic BP were observed in both ACEi- and VPI-treated
groups (33 ⴞ 3 and 37 ⴞ 2%, respectively). Compared with ACEi, VPI-treated rats displayed a significantly larger reduction
of plasma (41 ⴞ 5 versus 61 ⴞ 4%) and renal (53 ⴞ 6 versus 74 ⴞ 4%) ACE activity. It is concluded that both ACEi and VPI
intervention prevent renal damage in a rat model of cardiorenal interaction. VPI treatment seemed to provide no additional
renoprotection compared with sole ACEi after 6 wk of treatment in this model, despite a more pronounced ACE-inhibiting
effect of VPI.
J Am Soc Nephrol 17: 3059 –3066, 2006. doi: 10.1681/ASN.2006030209
R
ecent studies have disclosed a complex relationship
between cardiovascular and renal disease. Impaired
renal function is detrimental for the heart (renocardiac
interaction) both in clinical (1– 8) and in experimental (9,10)
settings. Impaired cardiac function is detrimental to the kidney
(cardiorenal interaction), which is less well characterized and
only in experimental settings. Recently, we described enhanced
progressive renal damage in a model of cardiorenal interaction
that was elicited by myocardial infarction (MI) in unilaterally
nephrectomized rats (11). The mechanism of this cardiorenal
interaction is unclear, but candidate mechanisms are hormonal
systems such as the renin-angiotensin-aldosterone-system
(RAAS) and the natriuretic peptide system (11). Both angioten-
sin-converting enzyme inhibition (ACEi) and neutral endopeptidase (NEP) inhibition (although controversial) have been
shown to be protective in progressive function loss of either the
kidney or the heart (12–15). The combination of ACE and NEP
inhibition is claimed to be more effective in this regard (16 –20).
Accordingly, the aim of our study was to investigate involvement of the RAAS and/or the natriuretic peptide system in the
pathophysiology of progressive renal damage after MI. We
investigated the renoprotective effects of ACEi with lisinopril
versus combined ACE/NEP inhibition with the vasopeptidase
inhibitor AVE7688 (21–23).
Materials and Methods
Experimental Protocol
Received March 7, 2006. Accepted August 9, 2006.
Published online ahead of print. Publication date available at www.jasn.org.
W.A.K.M.W. and W.B.A.E. contributed equally to this work.
S.S.’s current affiliation is Bayer Healthcare AG, Wuppertal, Germany.
Address correspondence to: Dr. Richard P.E. van Dokkum, Department of Clinical
Pharmacology, Groningen Institute for Drug Exploration, University Medical Center
Groningen, University of Groningen, Antonius Deusinglaan 1, NL-9713 AV, Groningen,
The Netherlands. Phone: ⫹31-50-363-2840; Fax: ⫹31-50-363-2812; E-mail:
r.p.e.van.dokkum@med.umcg.nl
Copyright © 2006 by the American Society of Nephrology
Male Wistar rats (320 to 350 g; n ⫽ 75) were housed under standard
conditions with free access to food and drinking water. Rats received a
standard chow diet that contained 19% protein (diet #1324; Altromin,
Lage, Germany). Animal experiments were approved by the institutional animal ethics committee.
At week ⫺2, all 75 rats underwent right unilateral nephrectomy
under anesthesia with 2.0% isoflurane in N2O/O2 (2:1) as described
previously (11). At week 0, rats were intubated, ventilated (AIV, Hoek
Loos, The Netherlands), and anesthetized using 2.0% isoflurane in O2.
MI was induced by ligation of the left anterior descending coronary
ISSN: 1046-6673/1711-3059
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Journal of the American Society of Nephrology
artery as described previously (24). Of these 75 rats, 30 died within 24 h
after MI surgery and were excluded from the study. Seventeen weeks
after MI, rats were stratified for proteinuria as a measure for renal
damage and assigned to one of the following treatment groups: (1)
vehicle (n ⫽ 12), (2) lisinopril 5 mg/kg per d (ACEi; n ⫽ 16), and (3)
AVE7688 21 mg/kg per d (VPI; n ⫽ 14). A 6-wk treatment period was
initiated up to week 23, when the rats were killed. Lisinopril (Merck,
Sharp & Dohme, Haarlem, The Netherlands) was administered
through the drinking water in a concentration of 75 mg/L, providing a
dosage of 5 mg/kg per d. AVE7688 (Sanofi-Aventis Pharma Deutschland, Frankfurt am Main, Germany) was mixed through the food at
a concentration of 450 ppm, resulting in a dosage of 21 mg/kg per d. In
a pilot experiment, these dosages resulted in comparable plasma ACEi.
At the end of the experiment, after measurement of functional cardiac
parameters under 2.5% isoflurane anesthesia, laparotomy was performed and rats were exsanguinated by taking blood samples from the
abdominal aorta for plasma measurements. The remaining kidney was
flushed with saline, and the heart and the kidney were removed and
weighed.
Functional Parameters
BP and Urinary Measurements. Systolic BP (SBP) was measured
using tail-cuff plethysmography (IITC Life Science, Woodland Hills,
CA) in trained awake, restrained rats. SBP was measured at baseline
and regularly thereafter until the end of study. Measurements of water
and food intake as well as 24-h urine collections for determination of
urinary total protein excretion and urine production were performed
weekly by placing the rats in metabolic cages.
Urine, Plasma, and Tissue Measurements. Urinary total protein
was analyzed using end-point measurement with TCA precipitation
(Nephelometer Analyzer II; Dade Behring, Marburg, Germany). As a
representation of renal function, creatinine clearance was calculated
from urinary and plasma creatinine levels at baseline, at stratification,
and at the end of the experiment. Creatinine was determined using
standard kits (Roche Diagnostics, Basel, Switzerland) on a Hitachi 912
E analyzer (Hitachi, Mountain View, CA). Plasma and renal ACE
activity were measured to evaluate the effect of treatment on ACEi
using the conversion of hippuryl-His-Leu (Sigma, St. Louis, MO) by
ACE to free His-Leu (25). Plasma renin activity was measured to
investigate the activity of the RAAS by a RIA (Adaltis Italy SPa,
Bologna, Italy), and pro-atrial natriuretic peptide (pro-ANP) was measured to investigate NEP inhibition using a sandwich enzyme immunoassay (Biomedica, Vienna, Austria).
Cardiac Function at the End of the Study
Under 2.5% isoflurane in O2 anesthesia, cardiac performance was
measured with a pressure transducer catheter that was inserted
through the right carotid artery (Micro-Tip 3French; Millar Instruments
Inc., Houston, TX), connected to a personal computer that was
equipped with an analog-to-digital converter and appropriate software
(Millar Instruments). After a 3-min period of stabilization, left ventricular end diastolic pressure (LVEDP), left ventricular end systolic pressure (LVESP), and heart rate were recorded. Thereafter, the catheter
was withdrawn into the aortic root to measure central SBP (SBPcentral).
As a parameter of global myocardial contractility and relaxation, we
determined the maximal rates of increase and decrease in left ventricular pressure (LVP) (systolic ⫹dP/dtmax and diastolic ⫺dP/dtmax),
J Am Soc Nephrol 17: 3059 –3066, 2006
which were normalized to left ventricular pressure change (i.e.,
LVESP ⫺ LVEDP) for individual rats.
Histology
Kidney. Kidneys were fixed by immersion for 48 h in a 4%
buffered formaldehyde solution (Klinipath, Duiven, The Netherlands) after longitudinal bisection and subsequently embedded in
paraffin according to standard procedures. An examiner who was
blinded for the groups evaluated all sections.
Mesangial Matrix Expansion, Focal Glomerulosclerosis, and Interstitial
Fibrosis. Sections of 3 ␮m were stained with periodic acid Schiff.
The degree of mesangial matrix expansion (MME) and focal glomerulosclerosis (FGS) were assessed in 50 glomeruli by scoring semiquantitatively on a scale of 0 to 4 (26). FGS was scored positive when
MME and adhesion to Bowman’s capsule were present in the same
quadrant. When one quadrant of the glomerulus was affected, a
score of 1⫹ was assigned, two quadrants was scored as 2⫹, three
quadrants as 3⫹, and four quadrants as 4⫹. Overall MME and FGS
score is expressed in arbitrary units (AU) with a maximum of 200.
Interstitial fibrosis (IF) was defined as expansion of the interstitial
space, with or without the presence of atrophied and dilated tubules
and thickened tubular basement membranes. The degree of IF was
assessed in 30 interstitial fields at ⫻20 magnification by scoring
semiquantitatively on a scale of 0 to 5 as follows: 0, no IF; 1, 1 to 10%;
2, 10 to 25%; 3, 25 to 50%; 4, 50 to 75%; and 5, 75 to 100%. The score
is given as AU with a maximum of 150.
Interstitial and Glomerular ␣-Smooth Muscle Actin and Glomerular
Surface Area. ␣-Smooth muscle actin (␣-SMA) was determined as a
profibrotic marker and detected in paraffin-embedded sections by
means of a mouse monoclonal ␣-SMA antibody (Sigma Chemical).
First, the antibody was incubated for 60 min, and its binding was
detected by sequential incubations with peroxidase-labeled rabbit
anti-mouse and peroxidase-labeled goat anti-rabbit antibody (both
from Dakopatts, DAKO, Glostrup, Denmark) for 30 min. The expression of interstitial ␣-SMA was measured by computerized morphometry. Therefore, 40 fields were scored at ⫻20 magnification in
the cortical region; glomeruli and vessels were excluded from measurement along Bowman’s capsule and the vessel wall. Glomerular
surface area, as a measure for glomerular hypertrophy, was measured using this procedure as well. For the expression of glomerular
␣-SMA, 40 glomeruli were scored at ⫻20 magnification. Total staining was expressed as percentage of total area surface.
Interstitial Macrophage Number. The number of interstitial macrophages was determined as an indication of the degree of inflammation. Therefore, a mouse monoclonal anti-rat monocyte and macrophage IgG1 (ED-1; Serotec, Oxford, England) was used. First, the
antibody was incubated for 60 min, and its binding was detected by
sequential incubations with peroxidase-labeled rabbit anti-mouse
and peroxidase-labeled goat anti-rabbit antibody (both from Dakopatts, DAKO) for 30 min. The expression of interstitial ED-1—
positive cells per field was measured by computerized morphometry. Therefore, 40 fields were scored at ⫻20 magnification in the
cortical region; glomeruli were excluded from measurement along
Bowman’s capsule. The average score was calculated per cortical
section.
Glomerular Desmin. Desmin, a marker for glomerular visceral
epithelial cell damage, was detected using a mouse mAb (clone
DE-R-11; Novocastra Laboratories Ltd, Newcastle, UK). For glomerular desmin staining, 30 glomeruli were scored semiquantitatively,
by estimating the percentage of desmin-positive glomerular visceral
epithelial cells (injured podocytes) in the outer cell layer of the
J Am Soc Nephrol 17: 3059 –3066, 2006
RAAS Inhibition in a Cardiorenal Interaction Model
glomerular tuft from 0 to 5 as follows: 0, no staining; 1, 1 to 10%; 2,
10 to 25%; 3, 25 to 50%; 4, 50 to 75%; and 5, 75 to 100% staining.
Desmin staining is presented in AU with a maximum of 150.
Heart.
Infarct Size. The heart was arrested in diastole in a cold 1-M KCl solution and weighed. The atria were dissected from the ventricles, and the right
free wall was separated from the left ventricle and weighed. Two left ventricular midsagittal slices (of approximately 2 mm) were fixed in 4% buffered
formaldehyde solution, embedded in paraffin, cut into 5-␮m slices, and
stained with 0.1% Sirius Red F3B (Klinipath, Duiven, The Netherlands) and
0.1% Fast Green FCF (Klinipath). Endo- and epicardial circumference of the
left ventricle and of scar tissue was determined by means of a computerized
planimeter (Image-Pro plus; Media Cybernetics Inc., Silver Spring, MD). MI
size was expressed as the mean of the inner and outer percentage of scar tissue
to the inner and outer total circumference of the left ventricle. All sections were
evaluated by an examiner who was blinded for the groups.
Statistical Analyses
All data are presented as mean ⫾ SEM. In general, differences between
the groups were compared using a one-way ANOVA for parameters
measured at one time point and an analysis of covariance for parameters
with two repeated measurements before and after the treatment period. A
general linear model for repeated measures was used to compare the
change in proteinuria and change in SBP curves during the treatment
phase (weeks 18 through 23). A Bonferroni post hoc test was used to
identify the differences between groups. A paired samples t test was used
to compare a parameter before and after treatment in one group. In all
tests, P ⬍ 0.05 was considered statistically significant.
Results
Overall Condition
In the vehicle- and ACEi-treated groups, body weight remained
stable during the treatment period, even as food intake and urine
production (Table 1). In the VPI-treated group, body weight significantly decreased during this period, whereas food intake remained stable and water intake increased. Differences in urine
production before and after treatment were not observed between
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groups. Water intake was significantly higher in the ACEi- and the
VPI-treated groups compared with vehicle.
Effects of Treatment Regimens on Plasma and Renal ACE
Activity, Levels of Renin, and Pro-ANP
At the end of the treatment period, plasma ACE activity was
significantly lower (41 ⫾ 5%) in the ACEi-treated group and in
the VPI-treated group (61 ⫾ 4%) compared with vehicle (Table
2). Renal ACE activity was significantly lower in the ACEitreated group (53 ⫾ 6%) and in the VPI-treated group (74 ⫾ 4%)
compared with vehicle (Table 2). Plasma and renal ACE activity
was significantly more inhibited in the VPI- compared with the
ACEi-treated group. Plasma renin activity was significantly
and equally higher in both the ACEi- and the VPI-treated
groups (Table 2) compared with vehicle. Pro-ANP levels were
significantly higher in the VPI- compared with the ACEitreated group (Table 2).
Cardiovascular Characteristics
Tail-cuff SBP remained stable from a baseline level of 134 ⫾
2 to 137 ⫾ 3 mmHg at stratification. At the end of the treatment
period, the groups that were treated with ACEi and VPI
showed a significant reduction in SBP compared with stratification (33 ⫾ 3 and 37 ⫾ 2%, respectively), whereas SBP remained stable in the vehicle-treated group (Figure 1A). The
BP-lowering effect was comparable in the ACEi- and VPItreated groups. Intra-arterially measured SBP (at the end of the
study) showed a comparable difference between vehicle and
both treatment groups (20 ⫾ 2 and 26 ⫾ 3% lower in ACEi and
VPI, respectively; Table 3).
MI size was comparable in all groups (Table 3). Total wet heart
weight was significantly lower in the ACEi- and VPI-treated
groups compared with the vehicle-treated group (Table 3).
LVESP and LVEDP were significantly lowered in the ACEiand VPI-treated groups compared with the vehicle-treated
Table 1. Rat characteristicsa
Characteristic
Body weight (g)
Food intake (g)
Water intake (ml/d)
Urine production (ml/d)
Total protein excretion (mg/d)
Creatinine clearance (ml/min per kg)
a
Time Point
VEH (n ⫽ 12)
ACEi (n ⫽ 16)
VPI (n ⫽ 14)
Stratification
End of study
Stratification
End of study
Stratification
End of study
Stratification
End of study
Stratification
End of study
Stratification
End of study
523 ⫾ 10
530 ⫾ 11
20 ⫾ 2
18 ⫾ 2b
31 ⫾ 4
27 ⫾ 4b
14 ⫾ 2
15 ⫾ 2
180 ⫾ 43
224 ⫾ 45b
4.0 ⫾ 0.2
3.7 ⫾ 0.4
513 ⫾ 9
525 ⫾ 9
18 ⫾ 1
19 ⫾ 1
33 ⫾ 2
35 ⫾ 2c
18 ⫾ 2
20 ⫾ 1
171 ⫾ 31
54 ⫾ 14b,c
5.1 ⫾ 0.2c
4.2 ⫾ 0.3b
530 ⫾ 8
516 ⫾ 7b
22 ⫾ 1
24 ⫾ 1b,c,d
34 ⫾ 2
40 ⫾ 3c
17 ⫾ 2
18 ⫾ 4
163 ⫾ 35
52 ⫾ 9b,c
4.3 ⫾ 0.2
3.4 ⫾ 0.3b
ACEi, angiotensin-converting enzyme inhibitor; VEH, vehicle; VPI, vasopeptidase inhibitor.
P ⬍ 0.05 versus stratification.
c
P ⬍ 0.05 versus VEH.
d
P ⬍ 0.05 versus ACEi.
b
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Table 2. Treatment effects at the end of the study
Parameter
VEH (n ⫽ 12)
ACEi (n ⫽ 16)
VPI (n ⫽ 14)
Plasma ACE (nmol HisLeu/ml per min)
Renal ACE (nmol HisLeu/ml per min)
Plasma renin activity (ng AngI/ml per h)
Pro-ANP (pmol/ml)
75 ⫾ 6
28 ⫾ 3
11 ⫾ 5
14 ⫾ 1.5c
45 ⫾ 4b
13 ⫾ 2b
24 ⫾ 2b
5 ⫾ 0.7b
30 ⫾ 4b,c
7 ⫾ 1b,c
25 ⫾ 4b
12 ⫾ 1.1c
a
AngI, angiotensin I; Pro-ANP, pro-atrial natriuretic peptide.
P ⬍ 0.05 versus VEH.
c
P ⬍ 0.05 versus ACEi.
b
Figure 1. Effect of treatment with angiotensin-converting enzyme inhibitor (ACEi) and vasopeptidase inhibitor (VPI) on systolic
BP (SBP; A) and proteinuria (B), given as change in SBP and change in proteinuria from stratification (week 17). *P ⬍ 0.001 versus
vehicle (VEH).
group (Table 3) and therefore were not different between ACEi
and VPI. The maximal rate of left ventricular isovolumetric
pressure development (⫹dP/dtmax) was significantly higher in
the ACEi- compared with the vehicle-treated group. A similar
trend, although not statistically significant, was observed in the
VPI-treated group (Table 3). The isovolumetric pressure decay
(⫺dP/dtmax) was not affected by therapy.
Renal Characteristics
Daily urinary total protein excretion increased in the entire
cohort from a baseline level of 16 ⫾ 1 to 167 ⫾ 20 mg/d at
stratification with comparable levels in all groups (Table 1).
After a subsequent treatment period of 6 wk, proteinuria was
significantly lower in the ACEi-treated group (76 ⫾ 6%) and in
the VPI-treated group (77 ⫾ 4%) compared with the vehicletreated group, in which proteinuria steadily increased to 224 ⫾
45 mg/24 h (Table 1). There was no significant difference in
antiproteinuric effect between both treatments (Figure 1B). At
the end of the treatment period, proteinuria was reduced by
ACEi to 105 ⫾ 22 mg/d compared with stratification and by
VPI to 110 ⫾ 28 mg/d.
When treatment was started, creatinine clearance was signif-
icantly reduced from a mean level of 10.6 ⫾ 0.5 ml/min per kg
at baseline to 4.5 ⫾ 0.2 ml/min per kg for the entire cohort,
corresponding to serum creatinine level of 42 ⫾ 1 ␮mol/L.
Although no significant difference in creatinine clearance was
observed at stratification between the ACEi- and VPI-treated
groups, there was a difference between the ACEi- and vehicletreated groups (Table 1). Corrected for the levels at stratification, no difference in treatment effect on creatinine clearance
was observed.
At the end of the study, no significant differences were
present in the wet weight of the remaining left kidney. Glomerular damage was investigated by measurement of glomerular
surface area, FGS, MME, glomerular ␣-SMA staining, and glomerular desmin staining (Figure 2). Glomerular surface area
was significantly smaller in ACEi- compared with the vehicletreated group. VPI treatment did not affect glomerular surface
area. FGS was significantly lower in ACEi- compared with the
vehicle-treated group, and a trend toward a lower level was
observed for the VPI-treated group (P ⫽ 0.11). Glomerular
␣-SMA staining was significantly lower after treatment with
both ACEi and VPI compared with the vehicle-treated group.
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RAAS Inhibition in a Cardiorenal Interaction Model
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Table 3. Cardiac parameters at the end of the studya
Parameter
VEH (n ⫽ 12)
ACEi (n ⫽ 16)
VPI (n ⫽ 14)
MI size (%)
Heart weight (g)
Heart rate (beats/min)
SBPcentral (mmHg)
LVEDP (mmHg)
LVESP (mmHg)
⫹dP/dtmax (/s)
⫺dP/dtmax (/s)
30 ⫾ 3
1.68 ⫾ 0.06
321 ⫾ 9
115 ⫾ 6
17 ⫾ 3
117 ⫾ 6
64 ⫾ 5
⫺85 ⫾ 2
24 ⫾ 4
1.40 ⫾ 0.05b
329 ⫾ 10
92 ⫾ 2b
12 ⫾ 1b
94 ⫾ 2b
81 ⫾ 3b
⫺86 ⫾ 2
29 ⫾ 4
1.38 ⫾ 0.03b
340 ⫾ 10
85 ⫾ 4b
11 ⫾ 1b
87 ⫾ 4b
77 ⫾ 4
⫺82 ⫾ 3
a
LVEDP, left ventricular end diastolic pressure; LVESP, left ventricular end systolic pressure; MI, myocardial infarction;
SBPcentral, central systolic BP.
b
P ⬍ 0.05 versus VEH.
No significant differences in MME were observed after treatment with ACEi and VPI compared with vehicle. The level of
desmin staining, as a measure for podocyte damage, was significantly lower after VPI treatment compared with both ACEi
and vehicle. Interstitial damage was investigated by the measurement of IF, interstitial ␣-SMA staining, and interstitial ED-1
staining (Figure 2). A trend toward lower levels of IF was
observed after treatment with ACEi (P ⫽ 0.2) and VPI (P ⫽ 0.2)
compared with vehicle. A significant lower interstitial ␣-SMA
staining was observed in both the ACEi- and the VPI-treated
groups compared with the vehicle-treated group. A similar
pattern was seen for the number of ED-1–positive cells.
Discussion
This study confirms our previous finding that MI induces
enhanced progressive renal damage in unilateral nephrectomized rats (11). This detrimental cardiorenal interaction can be
attenuated by treatment with either an ACE inhibitor or a VPI,
with substantial beneficial effects on kidney and heart. It is
interesting that the addition of NEP inhibition on top of ACEi
(as offered by the VPI) was devoid of extra protection.
Several mechanisms have been hypothesized, including hemodynamic alterations, involvement of the RAAS and sympathetic nervous system, endothelial dysfunction, and inflammation (27), which also are thought to interact with each other.
First, as far as the role of hemodynamics in explaining the
observed cardiorenal interaction is concerned, reduced cardiac
output after MI may lead to reduced renal perfusion, which in
turn could lead to compensatory RAAS activation. This RAAS
activation in turn can be detrimental to both heart and kidney.
An elevated angiotensin II level is known to interact with
cardiac function, leading to progressive cardiac function loss
(28), and elevated angiotensin II levels may lead to progressive
renal damage (29). It is interesting that RAAS intervention with
either ACEi or angiotensin II receptor blocker can protect both
heart and kidney (30,31). In our cardiorenal interaction model,
ACEi therapy was effective in the prevention of enhanced renal
damage that was caused by MI, because the level of proteinuria, interstitial and glomerular ␣-smooth muscle actin staining, glomerular surface area, and FGS incidence were significantly lower compared with those in the vehicle group. The
level of renal inflammation (ED-1 staining) seemed to be significantly lower in the ACEi-treated group. It is interesting that
cardiac contractility (⫹dP/dtmax) and LVEDP showed a more
favorable outcome in the ACEi- compared with the vehicletreated group at the end of the study. In view of these findings,
it is likely that the RAAS is of significant importance in this
cardiorenal interaction model. It should be taken into account,
however, that RAAS inhibition is invariably associated with BP
reduction. Therefore, lowering BP by means of a calcium channel blocker would be an interesting strategy to allow further for
a distinction between BP lowering per se and blockade of the
RAAS.
Regarding VPI treatment, it has been postulated that natriuretic peptides act on both the heart and the kidneys by vasodilation, natriuresis, diuresis, decreased cell growth, inhibition
of the sympathetic nervous system, and inhibition of the RAAS
(32). In our previous study, we found a trend toward a decrease
in natriuretic peptide levels in the group with combined cardiac
and renal damage, whereas in the group with only cardiac
damage, higher levels were observed (11). From this observation, we hypothesized a role for natriuretic peptides in the
deteriorating effect of the cardiorenal interaction. However, no
additional protective effect of VPI over ACEi on renal damage
as measured as FGS, proteinuria, and interstitial and glomerular ␣-smooth muscle actin staining was observed in our study.
Although VPI was more effective than ACEi in prevention of
podocyte damage, this did not result in the expected augmented prevention of increased proteinuria or FGS (33). Overall, this leaves only a little evidence for a discernible beneficial
effect of an increased level of natriuretic peptides beyond concurrent RAAS inhibition and associated BP reduction in this
cardiorenal model with short-term pharmacologic intervention.
Our study, however, does not exclude VPI still to have an
important clinical contribution in both “renal” and “cardiac”
patients, because VPI have proved to be effective in more
isolated renal and cardiovascular disease (18 –20,34).
Some caution is needed when interpreting the efficacy of
ACEi versus VPI treatment. First, an important issue relates to
finding equipotent dosages with respect to effects on BP and
plasma ACE activity. Although we performed a pilot experiment to determine dosage levels that yield a comparably re-
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J Am Soc Nephrol 17: 3059 –3066, 2006
Figure 2. Renal histologic characteristics. Representative photomicrographs and quantitative scoring of focal glomerulosclerosis
(FGS) and mesangial matrix expansion (MME; A), interstitial and glomerular ␣-smooth muscle actin (␣-SMA) staining (B),
interstitial fibrosis (IF; C), glomerular desmin staining (D), and ED-1–positive cells (E). 䡺, VEH; u, ACEi; f, VPI. *P ⬍ 0.05 versus
VEH; #P ⬍ 0.05 versus VEH and ACEi. Magnifications: ⫻40 in A and D; ⫻20 in B, C, and E.
duced level of plasma ACE activity with ACEi and VPI treatment in healthy rats, ACE activity was not reduced similarly by
both treatment regimens in our study, although effects on BP
were comparable. Besides this, no full dose-response relationships were established in our study. However, this would not
change substantially the interpretation of the data, because the
selected VPI dosage resulted in a larger reduction in ACE
activity. The effects on proteinuria, ␣-SMA, and FGS were
comparable. This might indicate a dissociation between the
level of ACEi and antiproteinuric effect of these drugs. Second,
despite the substantial increase in pro-ANP levels in the VPIcompared with the ACEi-treated group, the NEP inhibiting
component of the VPI may have insufficiently increased the
levels of natriuretic peptides at the selected dosage to provide
cardiorenal protection. Third, a VPI treatment period that is
longer than 6 wk may be required for the beneficial cardiorenal
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RAAS Inhibition in a Cardiorenal Interaction Model
effects of ANP to develop. Taal et al. (18) showed that the VPI
omapatrilat displayed favorable effects compared with the
ACEi enalapril at a treatment duration of 32 wk in five-sixths
nephrectomized rats, despite comparable efficacy in the short
term. Further long-term studies are needed to clarify this issue.
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6.
Conclusion
Our results demonstrate the efficacy of RAAS-inhibiting therapy to prevent the enhanced progression of renal damage after
MI in a model of mildly compromised renal dysfunction. This
intervention is of potential clinical relevance, because it breaks
a vicious circle: MI leading to cardiac dysfunction in turn
leading to renal dysfunction triggering further cardiac dysfunction. This, however, will require changes in prescribing behavior of doctors who treat patients after MI. Patients are not
regularly prescribed RAAS intervention after MI (35), whereas
“cardiac” patients with compromised renal function are being
approached with utmost care as far as RAAS intervention is
concerned (36). This is in favor of the recent view that these
drugs reduce long-term cardiovascular morbidity and mortality, apart from their direct effects on BP and proteinuria. Our
study further indicates that RAAS intervention after MI may
provide not only cardiac protection but also renal protection.
Acknowledgments
This study was financially supported by Sanofi Aventis Pharma
Deutschland.
We acknowledge J.J. Duker, Dr. M. Gerl, M. Goris, Dr. H. van Goor,
B.G. Haandrikman, F. Hut, B. Meijeringh, Dr. R. Schoemaker, J.W.J.T
van der Wal, and C. Wisselink for valuable advice and technical assistance. Lisinopril was a kind gift from Merck, Sharp & Dohme (Haarlem,
The Netherlands). AVE7688 was a kind gift from Sanofi Aventis
Pharma Deutschland.
Parts of this study were presented at the American Society of Nephrology Renal Week; November 8 through 13, 2005; Philadelphia, PA;
and have been published in abstract form (J Am Soc Nephrol 16: 215A,
2005).
7.
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