(Hypertension. 1998;32:1044-1048.)
© 1998 American Heart Association, Inc.
Scientific Contributions |
1-Adrenergic Plus Angiotensin Receptor Blockade Reduces Atherosclerosis in Apolipoprotein EDeficient Mice
From the Departments of Medicine and Biochemistry, Boston University School of Medicine, Boston, Mass.
Correspondence to Peter Brecher, PhD, Boston University School of Medicine, 715 Albany St, W507, Boston, MA 02118. E-mail pbrecher{at}bu.edu
| Abstract |
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1-adrenergic receptors influence
arteriosclerotic changes in this
hyperlipidemic animal model. Mice were treated with
antihypertensive drugs beginning at 9 weeks of age, and aortic
atherosclerosis was measured after 12 weeks of
treatment. Systolic blood pressure in the untreated
apoE-deficient mouse averaged 104 mm Hg throughout the treatment
period. Prazosin at a dose of 7.5 mg · kg-1
· d-1 was ineffective in attenuating
atherosclerosis and did not significantly reduce blood
pressure. Losartan, at dosages of either 20 or 30 mg ·
kg-1 · d-1, also did not influence
atherosclerosis and had only a slight blood
pressurelowering effect. However, combined treatment with both
prazosin and losartan markedly reduced atherosclerotic lesion
development from an average lesion size per section of 2.6 to
1.5x105 µm2 (P<0.001)
and significantly reduced blood pressure to 85±5 mm Hg.
Treatment with
NG-nitro-L-arginine methyl ester
(40 mg · kg-1 · d-1) produced
significant elevations of blood pressure (127±3.8 mm Hg) but had
no effect on the development of atherosclerosis. None
of the treatments used affected plasma cholesterol
throughout the 12-week period. These studies suggest that the vascular
changes associated with atherosclerosis are influenced
by a combination of AT1 and
1-adrenergic
receptor activation.
Key Words: atherosclerosis blood pressure losartan prazosin mice hypercholesterolemia
| Introduction |
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The
1-adrenergic system also has been
implicated in the development of atherosclerotic lesions. Adrenergic
stimulation caused DNA replication in medial smooth muscle
cells,7 and chronic
1-adrenergic stimulation increased DNA
synthesis in both uninjured and injured arteries in the
rat.8 Administration of prazosin appears to
suppress the mitogenic effect of catecholamines
in cultured rat aortic smooth muscle cells,9 and
doxazosin treatment reduced both serum lipid levels and the number of
macrophage-derived foam cells in the aortic arch of the
hypercholesterolemic
hamster.10
Recently, mice lacking the gene for apoE have been developed and found
to have both profound hypercholesterolemia and
the propensity to develop atherosclerotic lesions with many
similarities to those found in humans.11 In the
present study we have used the apoE-deficient mouse model to
determine whether inhibition of AT1
receptors and
1-adrenergic receptors might
prevent the development of atherosclerosis. These
studies suggest that the vascular changes affecting
atherosclerosis are influenced by combined effects
mediated by both the AT1 and the
1-adrenergic receptors.
| Methods |
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Animals
All mice used in these studies were purchased from the Jackson
Laboratory and designated C57BL/6J-apoE. These mice were apoE-deficient
female homozygotes (apoE-/-) that were backcrossed for 10 generations
to C57BL/6J at the Jackson Laboratories and were delivered to our
facilities at 8 weeks of age. The mice were maintained on a standard
chow diet (Purina, Certified Rodent Chow 5002) containing 4.5% fat and
given free access to both food and water throughout the study. After 1
week of acclimation to the animal quarters, drug treatment was
initiated, and the animals were maintained for 12 additional weeks on
the designated treatment. At 21 weeks of age the mice were killed with
an overdose of sodium pentobarbital.
Blood Pressure Measurements
Systolic blood pressure and heart rate measurements were
obtained in conscious mice using a computerized, noninvasive tail-cuff
system (BP 2000 Visitech Systems).12 Mice were
trained for 5 consecutive days (each session consisting of 20
unrecorded measurements) to familiarize the animals with the
tail-cuff apparatus. Subsequently, blood pressure and heart
rate measurements were obtained weekly for 12 consecutive weeks in all
treatment groups. One set of 20 measurements was obtained for each
mouse weekly, and the mean blood pressure and heart rate were
calculated.
Drug Treatment
Drugs were administered to the mice in the drinking water. The
solutions were prepared at 2- to 3-day intervals, and the
concentrations were based on the average volume of water consumed per
day (5 mL) and the body weight that increased progressively from about
19 to 22 g per mouse throughout the 12-week treatment period.
Plasma Cholesterol Measurements
Blood samples were obtained from the inferior vena
cava of anesthetized animals before the heart was removed for
morphometric analysis. Blood was drawn into tubes containing
EDTA and immediately centrifuged; total plasma
cholesterol was measured enzymatically using a commercially
available kit from Sigma Diagnostics.
Evaluation of Atherosclerotic Lesions
The heart and aorta were perfused with PBS and then
acetate-buffered formalin. The heart and proximal aorta were then
removed, weighed, and kept in formalin overnight. The heart was then
sliced with a scalpel to align the aortic root for subsequent
sectioning according to the procedure described by Paigen et
al.13 The tissue was processed and embedded in
paraffin using conventional procedures. Sections (5 µm) were
obtained from the region starting with the aortic sinus, and 5
sections, each spaced 50 to 60 µm apart, were saved for
morphometric analysis following the guidelines outlined by
Paigen et al.13 These sections were stained with
hematoxylin and eosin and photographed at a magnification of x40. The
images from these microscopic sections were scanned into a computer
using a Polaroid Sprint 35 scanner. The resulting images were then used
to quantify the lesion area measured using NIH Image 3.0 software by
carefully outlining the intimal lesion, which could readily be
distinguished from the media. The data from each of the 5 sections from
each animal were averaged and expressed as the lesion area per
section.
Statistical Analysis
All values are expressed as mean±SEM. Values for body and heart
weights, blood pressure, heart rate, plasma cholesterol,
and quantification of lesion size were compared using 1-way ANOVA.
Subsequent comparisons were performed using a 2-tailed unpaired
Student's t test.
| Results |
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Figure 3
shows
representative histological sections
stained with hematoxylin and eosin from 21-week-old control
apoE-deficient mice and those given the combination of prazosin and
losartan for 12 weeks. Consistent with other published
studies using the apoE knockout mouse, lesions were well developed by
21 weeks of age, consisting of both foam cells and fibrous plaques. The
size and severity of the lesions were visibly reduced by the combined
treatment. Sections from losartan- or prazosin-treated mice
were indistinguishable from the sections taken from 21-week-old
untreated apoE knockout mice (data not shown).
|
Effects of L-NAME and Propranolol Treatment
The Table
summarizes measurements of
lesion area and other parameters obtained after 12 weeks of
treatment in mice given L-NAME and
DL-propranolol. L-NAME did not affect the
progression of atherosclerosis, but it increased
systolic blood pressure significantly from 105 to as much as
127 mm Hg when given at a dosage of 40 mg ·
kg-1 · d-1. If
given at a lower dosage (20 mg ·
kg-1 · d-1), the
blood pressure elevation was less apparent and not statistically
significant. Again no change in atherosclerosis was
found. Neither L-NAME nor propranolol changed plasma
cholesterol or the heart weight/body weight ratio, but
L-NAME at the lower dosage did produce a slight but statistically
significant decrease in heart rate. Propranolol did not
alter either blood pressure or heart rate in the apoE mouse, and its
effect on atherosclerosis was not statistically
significant.
|
Temporal Effects of Various Drug Treatments on Systolic
Blood Pressure
Figure 4
summarizes systolic
blood pressure measurements from each of the 7 groups over the entire
12-week treatment period. Data at each weekly interval
represent recordings from 6 mice. Control mice averaged
between 102 and 107 mm Hg throughout the 12 weeks, with no
significant differences between any 2 weekly measurements. Values for
prazosin treatment alone did lower the pressure initially but became
indistinguishable from control values in the last 6 weeks of the
12-week treatment period. Treatment with prazosin+losartan
rapidly reduced the systolic pressure so that significant
reductions were found by the second week of treatment, and this effect
persisted throughout the entire treatment period. With losartan
treatment alone, the reductions were significant with some but not all
weeks of treatment, with significant but moderate reductions at 12, 14,
20, and 21 weeks of age. As shown above, only the combined treatment
was effective in reducing the progression of
atherosclerosis in this animal model.
Propranolol treatment at the dosage used (40 mg ·
kg-1 · d-1) was
ineffective in reducing blood pressure in the apoE-deficient mouse. The
elevation of blood pressure by L-NAME treatment was most obvious with
the higher dosage of the drug, where significant increases were seen
throughout the treatment period. Even with the lower dosage,
significant increases were observed, but this effect did not occur
consistently throughout the treatment period.
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| Discussion |
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A role for blood pressure reduction in reducing atherosclerosis may be indicated by our findings. The combined treatment with prazosin+losartan produced a striking reduction in blood pressure that was both rapid and more pronounced than that seen with losartan treatment alone. Studies using ACE inhibitors in genetically hypercholesterolemic rabbits also found results that could be explained in part by blood pressure effects.14 Our studies with L-NAME treatment clearly showed an increased systolic pressure but no effect on the severity or size of the atherosclerotic lesion, suggesting that increased blood pressure per se does not necessarily accelerate atherosclerosis in this model. In contrast, a study using a 1-kidney, 1-clip model of renovascular hypertension in the Watanabe heritable hyperlipidemic rabbit produced blood pressure increases of 40 to 60 mm Hg over levels in normotensive controls and led to enhanced atherosclerosis after either a 3- or 6-month treatment period.15 Another study using hypercholesterolemic rabbits has indicated that L-NAME treatment, even at dosages that did not elevate blood pressure, also increased atherosclerosis.16 Species differences between the hypercholesterolemic rabbit and apoE knockout mice with respect to the factors influencing atherosclerosis make interspecies comparisons difficult.
Our studies on losartan are directly in conflict with a recent report showing that losartan treatment inhibited atherosclerosis in the apoE-deficient mouse. In that study,6 mice were treated with losartan (25 mg · kg-1 · d-1) for 12 weeks, and atherosclerosis measured at the age of 5 months was reduced by 80%, an effect attributed to changes in LDL lipid peroxidation. We have no explanation for the striking difference between this study and our own, but in mice from the Jackson Laboratories we have reproduced our findings with losartan treatment in 2 separate experiments conducted several months apart and found no effect of losartan at 20 or 30 mg · kg-1 · d-1 after a 12-week treatment period. Over a period of 2 years we have reproducibly found that the atherosclerotic index of 21-week-old female mice averaged 2.6x105 µm2 per section, whereas the comparable value found in the study of Keidar et al6 was 0.80x105 µm2 per section.
The relationship between ACE activity and atherosclerosis was studied recently by Krege et al,17 who showed that when mice with a mutation that affects ACE activity were bred with mice heterozygous for apoE gene disruption, the reduction in ACE activity had no effect on the progression of atherosclerosis induced by a cholesterol-rich diet. Those studies, which suggested that genetic variation in the level of ACE does not affect the development of atherosclerosis, are consistent with our findings that losartan did not influence the course of atherosclerosis in the homozygous apoE knockout mouse fed a normal diet. ACE inhibitors have been shown to reduce atherosclerosis in both the Watanabe heritable hypercholesterolemic rabbit and the cholesterol-fed rabbit model,18 suggesting either a role for bradykinin or that the effect of angiotensin II in the progression of atherosclerosis may differ in mice and rabbit models. This seems to be the case for probucol treatment, which reduced atherosclerosis in the Watanabe heritable hypercholesterolemic rabbit19 but increased atherosclerosis in the apoE-deficient mouse model.20
Other mechanistic explanations for the combined effects of an
AT1 and
1-adrenergic
antagonist could involve direct effects on the cell types
often associated with the pathogenesis of
atherosclerosis. Because of the complex interactions
that occur in vivo over prolonged periods, it is difficult to define
the precise mechanism(s) responsible for this novel in vivo effect, but
our results do indicate that combined treatment with both prazosin and
losartan results in a significant inhibition of
atherosclerosis in a hyperlipidemic
animal model that has many characteristics comparable to lesion
development in humans.
| Acknowledgments |
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Received June 8, 1998; first decision July 15, 1998; accepted August 26, 1998.
| References |
|---|
|
|
|---|
2.
Chobanian AV, Haudenschild CC, Nickerson C, Drago R.
Antiatherogenic effect of captopril in the Watanabe heritable
hyperlipidemic rabbit. Hypertension. 1990;15:327331.
3. Kowala MC, Grove RI, Aberg G. Inhibitors of angiotensin converting enzyme decrease early atherosclerosis in hyperlipidemic hamsters: fosinopril reduces plasma cholesterol and captopril inhibits macrophage-foam cell accumulation independently of blood pressure and plasma lipids. Atherosclerosis. 1994;108:6172.[Medline] [Order article via Infotrieve]
4. Aberg G, Ferrer P. Effects of captopril on atherosclerosis in cynomolgus monkeys. J Cardiovasc Pharmacol. 1990;15(suppl 5):S65S72.
5. Kabour A, Henegar JR, Devineni VR, Janicki JS. Prevention of angiotensin II induced myocyte necrosis and coronary vascular damage by lisinopril and losartan in the rat. Cardiovasc Res. 1995;29:543548.[Medline] [Order article via Infotrieve]
6. Keidar S, Attias J, Smith J, Breslow JL, Hayek T. The angiotensin-II receptor antagonist, losartan, inhibits LDL lipid peroxidation and atherosclerosis in apolipoprotein E-deficient mice. Biochem Biophys Res Commun. 1997;236:622625.[Medline] [Order article via Infotrieve]
7.
van Kleef EM, Smits JF, De Mey JG, Cleutjens JP,
Lombardi DM, Schwartz SM, Daemen MJ. Alpha
1-adrenoreceptor blockade reduces the
angiotensin IIinduced vascular smooth muscle cell DNA
synthesis in the rat thoracic aorta and carotid artery. Circ
Res. 1992;70:11221127.
8.
deBlois D, Schwartz SM, van Kleef EM, Su JE, Griffin
KA, Bidani AK, Daemen MJ, Lombardi DM. Chronic alpha
1-adrenoreceptor stimulation increases DNA synthesis in
rat arterial wall: modulation of responsiveness after
vascular injury. Arterioscler Thromb Vasc Biol. 1996;16:11221129.
9.
Yu SM, Tsai SY, Guh JH, Ko FN, Teng CM, Ou JT.
Mechanism of catecholamine-induced proliferation of
vascular smooth muscle cells. Circulation. 1996;94:547554.
10. Kowala MC, Nicolosi RJ. Effect of doxazosin on plasma lipids and atherogenesis: a preliminary report. J Cardiovasc Pharmacol. 1989;13(suppl 2):S45S49.
11. Breslow JL. Mouse models of atherosclerosis. Science. 1996;272:685688.[Abstract]
12.
Krege JH, Hodgin JB, Hagaman JR, Smithies O. A
noninvasive computerized tail-cuff system for measuring blood pressure
in mice. Hypertension. 1995;25:11111115.
13. Paigen B, Morrow A, Holmes PA, Mitchell D, Williams RA. Quantitative assessment of atherosclerotic lesions in mice. Atherosclerosis. 1987;68:231240.[Medline] [Order article via Infotrieve]
14.
Chobanian AV, Hope S, Brecher P. Dissociation between
the antiatherosclerotic effect of trandolapril and suppression of serum
and aortic angiotensin-converting enzyme activity in the
Watanabe heritable hyperlipidemic rabbit.
Hypertension. 1995;25:13061310.
15.
Chobanian AV, Lichtenstein AH, Nilakhe V, Haudenschild
CC, Drago R, Nickerson C. Influence of hypertension on aortic
atherosclerosis in the Watanabe rabbit.
Hypertension. 1989;14:203209.
16.
Cayatte AJ, Palacino JJ, Horten K, Cohen RA. Chronic
inhibition of nitric oxide production accelerates
neointima formation and impairs endothelial
function in hypercholesterolemic rabbits.
Arterioscler Thromb. 1994;14:753759.
17. Krege JH, Moyer JS, Langenbach LL, Peng L, Zhang SH, Maeda N, Reddick RL, Smithies O. Angiotensin-converting enzyme gene and atherosclerosis. Arterioscler Thromb Vasc Biol. 1997;17:12451250.
18. Chobanian AV. Can antihypertensive drugs reduce atherosclerosis and its clinical complications? Am J Hypertens. 1994;7:119S125S.[Medline] [Order article via Infotrieve]
19.
Kita T, Nagano Y, Yokode M, Ishii K, Kume N, Ooshima A,
Yoshida H, Kawai C. Probucol prevents the progression of
atherosclerosis in Watanabe heritable
hyperlipidemic rabbit, an animal model for familial
hypercholesterolemia. Proc Natl Acad Sci
U S A. 1987;84:59285931.
20. Zhang SH, Reddick RL, Avdievich E, Surles LK, Jones RG, Reynolds JB, Quarfordt SH, Maeda N. Paradoxical enhancement of atherosclerosis by probucol treatment in apolipoprotein E-deficient mice. J Clin Invest. 1997;99:28582866.[Medline] [Order article via Infotrieve]
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