CARDIOVASCULAR JOURNAL OF AFRICA • Vol 21, No 5, September/October 2010
AFRICA
257
Effect of the haeme oxygenase-1/endogenous carbon
monoxide system on atherosclerotic plaque formation
in rabbits
DA-NAN LIU, YING FANG, LI-RONG WU, XING-DE LIU, PING LI, ZUO-YUN HE
Summary
Objective:
To investigate the effect of the haeme oxygenase-1/
carbon monoxide (HO-1/CO) system on atherosclerotic
plaque formation and its possible mechanism.
Methods:
For 12 weeks, rabbits were given a 1.5% cholesterol
diet (Ch group,
n
=
8) or a 1.5% cholesterol diet plus an HO-1
inducer, haemin (Hm group,
n
=
8), or an HO-1 inhibitor, zinc
protoporphyrin IX (Znpp-IX, Zn group,
n
=
8) by intraperi-
toneal injection.
Results:
Compared with the normal control group (C group,
n
=
8), serum levels of lipids and oxidised low-density lipo-
proteins (ox-LDL) increased significantly in all experimen-
tal groups (
p
<
0.01). However, no significant differences
were observed among the three experimental groups (
p
>
0.01). Compared with the control group, aortic nitric oxide
(NO) production and nitric oxide synthase (cNOS) activ-
ity decreased markedly, whereas carbon monoxide (CO)
production and HO-1 activity increased markedly in the
Ch group (
p
<
0.01). This was associated with an increase in
the area of aortic plaque of 54.00
±
4.16%. Compared with
the Ch group, CO production and HO-1 activity increased
markedly, while aortic HO activity and CO production
decreased significantly in the Hm group. The area of aortic
plaque was significantly reduced in the Hm group (17.88
±
3.01%), whereas the area of aortic plaque was significantly
increased in the Zn group (61.13
±
3.50%). Compared with
the Ch group, aortic endothlin-1 expression in the Hm group
reduced significantly, while in the Zn group it was signifi-
cantly higher than in the Ch group (
p
<
0.01).
Conclusion:
The HO-1/CO system plays an inhibitory role
in atherosclerotic plaque formation. This role was not medi-
ated by regulating serum lipids and ox-LDL, but was related
to the reciprocal relationship between the HO-1/CO and
NOS/NO systems in atherosclerosis and the down-regulated
expression of endothlin-1 (ET-1), which inhibits the prolifera-
tion of vascular smooth muscle cells.
Keywords:
atherosclerosis, carbon monoxide, nitric oxide
synthase, haeme oxygenase
Submitted 2/9/09, accepted 10/3/10
Cardiovasc J Afr
2010;
21
: 257–262
DOI: CVJ-21.001
Endogenous carbon monoxide (CO) is produced from the oxida-
tion of haemoglobin by haeme oxygenase (HO). CO is consid-
ered an important messenger molecule, with a similar effect
on cardiovascular function as nitrous oxide (NO). It activates
soluble guanylate cyclase (sGC) and increases cGMP levels,
thereby relaxing vascular smooth muscle and inhibiting platelet
aggregation and smooth muscle cell proliferation.
1–4
Some stud-
ies have shown that the HO/CO system plays an important role in
the inhibition of atherosclerotic plaque formation. However, the
specific mechanism and targets are unclear.
In our present study, NOS activity, HO-1 and endothlin-1
(ET-1) expression and the production of NO and CO were evalu-
ated in normal control rabbits, rabbits fed a diet high in choles-
terol, those not treated and those treated for 12 weeks with either
haemin (an HO inducer) or zinc protoporphyrin IX (an HO inhib-
itor) in order to investigate the effects of the HO-1/CO system on
atherosclerotic plaque formation and its regulatory mechanism.
Methods
The animal centre of Xinqiao Hospital provided 32 New Zealand
white rabbits weighing 1.6 to 2.0 kg. The experiment was started
after one week of adaptive feeding. The rabbits were randomly
divided into four groups: a cholesterol group (
n
=
8, Ch group),
a haeme group (
n
=
8, Hm group), a zinc protoporphyrin
IX (Znpp-IX) group (
n
=
8, Zn group) and a normal control
group (
n
=
8, C group). The rabbits in the C group were fed a
normal diet and those in the Ch group were fed a diet contain-
ing 1.5% cholesterol. The rabbits in the Hm and Zn groups
were fed a high-cholesterol diet, plus haemin (an HO inducer,
15 mg.kg
-1
.d
-1
) in the Hm group, or zinc protoporphyrin IX (an
HO inhibitor, 45
m
mol.kg
-1
) in the Zn group for 12 weeks by
intraperitoneal injection daily.
Blood samples were collected via the ear vein after 12 hours
of fasting and aortic tissue was harvested as described below.
Cholesterol powder (chemically pure) was imported from the
Netherlands and sub-packaged in Guangzhou. Haemin and
Znpp-IX were purchased from Sigma (USA). All procedures
were performed in accordance with the animal care guidelines of
GuiyangMedicalCollege,whichconformtotheNationalInstitutes
of Health Guide for the Care and Use of Laboratory Animals.
The ethics committee of our college also approved this study.
Preparation of aortic samples
At the end of the 12th week, all rabbits were anesthetised by
injection of 3% pentobarbital sodium (30 mg/kg) via the ear
Department of Cardiology, Affiliated Hospital, Guiyang
Medical College, Guiyang, China
DA-NAN LIU, MD,
YING FANG, MD
LI-RONG WU, MD
XING-DE LIU, MD
PING LI, MD
Department of Cardiology, Xinqiao Hospital, Third Military
Medical University, Chongqing, China
ZUO-YUN HE, MD
