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(Circulation. 1999;99:879-882.)
© 1999 American Heart Association, Inc.
Clinical Investigation and Reports |
From the Clinic for Cardiac Surgery, Institute of Medical Microbiology (M.M.), Institute of Pathology (R.M., A.C.F.), University of Luebeck, Luebeck, Germany.
Correspondence to C. Bartels, MD, Clinic for Cardiac Surgery, Medical University Lübeck, Ratzeburger Allee 160, 23538 Lübeck, FRG.
| Abstract |
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Methods and ResultsThirty-eight occluded coronary artery vein grafts and 20 native saphenous veins were examined. Detection of C pneumoniae DNA was performed by use of nested polymerase chain reaction (PCR). Homogenisates from the specimen were cultured for identification of viable C pneumoniae. Both conventional PCR and quantitative PCR for detection of CMV DNA were applied. Differential pathological changes (degree of inflammation, smooth muscle cell proliferation [MIB-1]) were determined and correlated to the detection of both microorganisms. C pneumoniae DNA could be detected in 25% of occluded vein grafts. Viable C pneumoniae was recovered from 16% of occluded vein grafts. Except for 1 native saphenous vein, all control vessels were negative for both C pneumoniae detection and culture. All pathological and control specimens were negative for CMV DNA detection. Pathological changes did not correlate with C pneumoniae detection.
ConclusionsOccluded aorto-coronary venous grafts harbor C pneumoniae but not CMV. The detection of C pneumoniae in occluded vein grafts warrants further investigation.
Key Words: viruses bypass atherosclerosis coronary disease
| Introduction |
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| Methods |
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Pathological and Control Specimens
A total of 38 occluded vein grafts from 32 consecutive patients
undergoing reoperations were collected (6 patients had 2 grafts
removed). Each patient contributed only once to the analysis of
demographic variables; in no case of repeat observations there was
any inconsistency regarding the detection of C
pneumoniae/CMV in the 2 different vein grafts obtained from the
same patient.
Only occluded vein grafts showing typical thickening of the venous
wall, indicative for late graft occlusion, were selected for further
investigation.8 Vein grafts were dissected free from the
adjacent tissue as far as technically possible. A
representative specimen of the occluded vein graft was
selected for further analysis. Mean interval from primary
surgery to reoperation was 105±50 months. Patient characteristics for
C pneumoniae positive and negative results are summarized in
the Table
. Twenty native saphenous veins served as controls: 16 veins
collected during primary surgery, and 4 veins obtained during
reoperation.
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C pneumoniae Detection
Three different segments of the occluded vein grafts were
selected for analysis. Tissue was cut into 0.3-cm segments,
ground, and suspended in cell culture medium. Suspensions were then
divided for polymerase chain reaction (PCR) and culture.
C pneumoniae PCR
Genomic C pneumoniae DNA was detected by a nested PCR
protocol as described.9 Briefly, DNA was purified
from the plaque suspensions by proteinase K digestion and
cetyltrimethylammonium bromide treatment. Nested PCR was then performed
with the species-specific HL-1/HR-1 primer pair (438 bp). The nested
primer pair IN-1/2 that yields a 128 bp product. For confirmation,
nonradioactive DNA hybridization was performed with
oligonucleotide HM-1 3'-labeled with digoxigenin-ddUTP
(Boehringer Mannheim) as the probe.
C pneumoniae Culture
Serum-free cell culture was performed as previously
described.9 10 Essentially, suspensions were
centrifuged onto HEp-2 host cell monolayers and incubated for 3
days at 35°C, 5% CO2, in isolation medium
(Eagle's Minimal Essential Medium, GIBCO/BRL) supplemented with 1
µg/mL cycloheximide (Sigma). Productive C pneumoniae
growth was identified by staining inclusions with FITC-conjugated
C pneumoniaespecific mouse monoclonal antibody
(Cellabs).
CMV Detection
DNA isolation and purification were performed (Qui amp Tissue
kit, Quiagen). Oligonucleotide primers (TIB MOLBIOL)
and probes (PE Applied Biosystems) complementary to the pp65 gene were
used.
Conventional CMV PCR
PCR was performed in a total volume of 50 µL consisting of
1xPCR buffer, 2.5 U AmpliTaq Gold (PE Applied Biosystems), 200
µmol/L of each dATP, dCTP, dGTP, dTTP, and 50 pmol of each primer.
PCR was performed by 40 cycles after activation of AmpliTaq Gold:
each cycle consisted of denaturation at 95°C for 10 seconds,
annealing 30 seconds, 62°C, and extension 30 seconds, 72°C (352
bp).
The reaction mixture was then subjected to agarose gel electrophoresis, Southern blotting, and nonradioactive hybridization with digoxigenin-labeled oligonucleotide probe as previously described.11
Quantitative CMV PCR
To obtain PCR conditions with reduced variability and
contamination, quantitative PCR was performed with real-time Taqman
(ABI PRISM 7700 Sequence Detector Systems, PE Applied
Biosystems).12 13 Premixes containing all reagents except
for targets were prepared, aliquoted into PCR tubes, and
analyzed. No template controls and positive CMV controls (0.5
ng CMV, total virus genome, Kreatech) paralleled each sample
analysis. The hybridization probe that binds to both PCR
products was labeled with a reporter dye, FAM, on the
5'-nucleotide and a quenching dye, TAMRA, on the
3'-nucleotide.14 PCR conditions were optimized
for oligonucleotide and MgCl2
concentrations. The following composition of PCR assay (total volume 50
µL) was used: 100 ng purified sample DNA, 15 pmol of each primer, 10
pmol probe, and 200 µmol/L of each of dATP, dCTP, dGTP, and
dTTP. The reaction conditions for 50 cycles after activation of
AmpliTaq Gold were 95°C, 15 seconds (denaturation) and 55°C, 1.5
minutes (annealing) (101 bp). Serial dilution of CMV DNA for
identification of CMV DNA detection threshold depicted positive CMV DNA
down to 12 copies.
Histomorphological Studies
The occluded vein grafts were investigated in consecutive series
by 2 independent investigators. The pathologists were unaware of
clinical data or detection of microorganisms. Thrombotic changes,
inflammation with respect to the extent of inflammation of vessel wall
circumference, differential analysis of contributing cells
(macrophages, lymphocytes, granulocytes, plasma cells, foam
cells, fibroblasts), and fibrotic changes within the
neointima were documented by histological
examination (paraffin section, hematoxylin-eosin staining).
Smooth muscle cell proliferation was examined by immunohistochemical staining, with the monoclonal antibody MIB-1 (Ki 67 antigen, Dianova). The antigen was unmasked by incubating sections in 10 mmol/L citrate buffer, pH 6.0, and boiling in a microwave oven for 20 minutes at a power level of 159 W (Miele supratonic 752). As an immunohistochemical detection system, the ABC technique in accordance to Hsu et al15 was used. One vessel wall circumference or 400 smooth muscle cells were examined for positive staining.
Statistical Analysis
Statistical analysis was performed with Minitab (Release
10). Continuous variables were analyzed with the 2-sample
t test (in the case of normal distribution) or Mann-Whitney
U rank-sum test. Binary data were analyzed with
Fisher's exact test. All tests were 2 tailed. A value of
P<0.05 was considered to indicate statistical
significance.
| Results |
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Demographic variables did not correlated with the positive detection of C pneumoniae by PCR or culture.
CMV Detection
All examined pathological and control specimens were negative for
CMV DNA detection by conventional and quantitative PCR.
Histomorphological Studies
No differences regarding histomorphological changes were detected
comparing C pneumoniae positive or negative occluded vein
grafts.
Proliferation rate of neointimal smooth muscle cells showed no association to the detection of C pneumoniae genome or culture.
| Discussion |
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Cytomegalovirus
Restenosis after coronary angioplasty has been
suggested to be causally related to reactivated CMV
infection.16 17 Intimal thickening of CABG presents a
unique form of accelerated atherosclerosis that shares
some similarities to restenosis following coronary
angioplasty.18 19 20 In this study neither in occluded CABG
nor in native saphenous veins could CMV DNA be detected. This negative
result was somewhat surprising because of the reported high prevalence
of positive CMV DNA detection in atherosclerotic
tissues.5 6 Two groups reported negative CMV genome
detection in atherosclerotic lesions: Benditt et al21
could not detect CMV viral mRNA in atherosclerotic arterial
wall tissue. Kol et al22 searched for the CMV major
immediate early gene mRNA (PCR) in tissue obtained from 20 patients
with unstable angina undergoing coronary atherectomy. As the
CMV major immediate early gene is indicative for replicative CMV, and
the authors did not observe a single positive PCR result, they
concluded that CMV replication is not a cause of unstable angina.
Therefore, in the present study we did not investigate the
detection of CMV gene products indicating viral replication but the
presence of CMV DNA itself.
Our results obtained by the use of highly sensitive and specific methods indicate that endovascular CMV presence does not seem to be associated with advanced vein graft disease.
Animal models demonstrated that CMV may induce atherosclerosis.23 Accelerated atherosclerosis, like vein graft disease, differs from spontaneous native atherosclerosis regarding vascular injury mechanism, pathological appearance, and duration of pathological process.1 Therefore, our negative CMV DNA detection in occluded vein grafts does not exclude an association between initiation of native coronary artery disease and CMV infection.
C pneumoniae
Preliminary results from our group reported detection
of C pneumoniae in occluded vein
grafts.9 This observation prompted us to
systematically study the prevalence of C pneumoniae in
occluded vein grafts and native saphenous veins. C
pneumoniae detection was frequent in occluded CABG: PCR 25% and
positive culture 16%. In 2 patients, C pneumoniae could be
detected in 2 separate vein grafts, indicating that endovascular
presence of C pneumoniae is not limited to 1 graft only.
Except for 1 native saphenous vein collected during reoperation from a
patient with positive C pneumoniae PCR in the occluded CABG,
all control vessels were negative for culture and PCR. Thus it may be
assumed that native saphenous veins do not harbor C
pneumoniae at implantation but that colonization takes place in a
relatively short time frame. This finding may be of significance for
the unresolved problem of rapid vein graft occlusion.
Vein grafts are subjected to mechanical injury during harvesting that initiates a healing process involving macrophages. Occlusion of vein graft is thrombotic in origin leading to leukocyte migration in the organized thrombus.1 C pneumoniae replicate within alveolar cells and spread systematically using macrophages and monocytes as vectors.24 Thus macrophage migration into the healing vein wall or organized thrombus may account for the detection of C pneumoniae in occluded vein grafts. Whether chronic macrophage infection contributes to local inflammation and plaque initiation or progression remains unclear. It has been suggested that vein graft occlusion may be immune-mediated.20 C pneumoniae infection appears to induce chronic immune activation mediated by cytokines.24 25 Whether cytokine mediated, direct endothelial cell damage or systemic inflammatory response stimulating acute phase proteins (eg, fibrinogen, C-reactive protein) is responsible for the observed association between chronic infection and atherosclerosis remains to be determined.26
Histomorphology
An interactive role of chronic infection with C
pneumoniae and/or CMV, inflammation, and coronary artery
disease has been suggested.7 27 However, it remains
unclear whether the local presence of the mentioned microorganisms or
systemic inflammatory changes are responsible for the observed
association between chronic infection and
atherosclerosis.5 Ocular infection with
Chlamydia trachomatis causes conjunctival infiltration by
macrophages and lymphocytes. Therefore, specific
histological changes, including inflammatory cell
subtypes correlated to the endovascular of C pneumoniae may
enlighten the underlying mechanism of vessel wall damage. Both C
pneumoniae and CMV may induce the induction of cytokines.
Cytokines stimulate fibroblast and smooth muscle cell
proliferation.7 More recently, Kol et
al27 demonstrated that C pneumoniae heat shock
protein 60 is localized in human atheroma and regulates
tumor necrosis factor and metalloproteinase expression. In the
present study, neither specific inflammatory changes nor extent of
smooth muscle cell proliferation could be correlated to the
endovascular presence of C pneumoniae. However, these
results are based on a relatively small number of examined
specimen.
Limitations of the Study
Local quantification of different cytokines in correlation
to the endovascular presence of C pneumoniae/CMV and
possible consecutive increased smooth cell proliferation may help to
clarify the underlying pathological mechanism. In the present
study, cytokines were not examined and thus cannot be
correlated to the observed level of smooth muscle cell proliferation.
Further studies quantifying the level of cytokines (eg,
TNF-
, -interleukin-1, -4, and -6) and comparing these levels with
the proliferation rate of smooth muscle cells are warranted to further
elucidate the underlying mechanism of vessel damage by C
pneumoniae.
Detection of both microorganisms and histomorphological analysis were performed in different parts of the occluded vein grafts. Therefore, no direct correlation of morphologic changes to the presence of C pneumoniae can be performed. However, as C pneumoniae nested PCR was reproducible positive in the analyzed three specimen from 1 occluded vein graft, it can be speculated that C pneumoniae genome was present in the specimen selected for pathological examination.
Therefore, the following conclusions can be drawn from the our results: Occluded venous coronary-artery bypass grafts but not native control veins harbor viable C pneumoniae and C pneumoniae DNA. No correlation between demographic characteristics and the positive detection of C pneumoniae could be observed. CMV does not seem to persist in occluded vein grafts; whether CMV initiates vein graft disease remains to be determined.
The observed detection of C pneumoniae DNA and viable C pneumoniae in occluded vein grafts warrants further investigation.
| Acknowledgments |
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| Footnotes |
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Received September 14, 1998; revision received November 4, 1998; accepted November 11, 1998.
| References |
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and matrix
metalloproteinase expression. Circulation. 1998;98:300307.The present study examined whether the
unresolved problem of venous coronary-artery bypass graft
occlusion can be related to infection with Chlamydia
pneumoniae and/or cytomegalovirus. Thirty-eight
coronary artery vein grafts and 20 native saphenous veins were
examined. Occluded aorto-coronary venous grafts harbor C
pneumoniae (polymerase chain reaction positive 25%; culture
positive 16%) but not cytomegalovirus. The detection of C
pneumoniae in occluded vein grafts warrants further
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