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Articles |
1
Servicio Cardiología, Hospital de Cabueñes, 33280 Gijón, Spain.
2
Laboratorio Genética Molecular-Instituto
Investigación Nefrológica and
3
Servicio
Cardiología, Hospital Central de Asturias, 33006 Oviedo, Spain.
4
Servicio Medicina Interna, Hospital Monte Naranco,
E-33006 Oviedo, Spain.
a Author for correspondence. Fax 34-985-273657; e-mail
ecoto{at}hcas.Insalud.es
| Abstract |
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Methods: To determine whether the DNA polymorphisms in
APOE (
2,
3, and
4 alleles), AGT
(M235T), AT1R (1166 A/C),
and ACE (I/D) are
associated with early onset of myocardial infarction (MI), we genotyped
220 patients and 200 controls <55 years of age. Patients and controls
were males from the same homogeneous Caucasian population. Data
concerning hypertension, diabetes, and tobacco consumption were
recorded. The lipid profiles of patients and controls were also
determined.
Results: APOE, ACE,
AGT, and AT1R allele and genotype
frequencies did not differ between patients and controls. None of these
polymorphisms was related to the biochemical values in patients
or controls. The frequency of individuals who were both
APOE
4 allele carriers
and AGT-TT homozygotes was significantly higher in
patients than in controls (11% vs 3.5%; P =
0.0037). In patients, the frequency of
4 carriers was significantly higher
(P <0.00001) in those who were AGT-TT
(46%) than those who were AGT-MT/MM
(14%). Mean cholesterol was significantly higher in
AGT-TT + APOE
34/44 patients than in the
TM/MM +
34/44 or
TT +
23/33 genotypes
(P = 0.029).
Conclusions: Our data suggest a synergistic effect between the
APOE and AGT polymorphisms and early MI.
The increased risk could be mediated in part through higher cholesterol
concentrations among individuals who are AGT-TT +
APOE
4 allele
carriers.
| Introduction |
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2,
3, and
4) have been
described. These alleles differ in the amino acids at residues 112 (Cys
in
3 and
2, and Arg
in
4) and 158 (Arg in
3, Cys in
2, and Arg
in
4) (1)(2). The
APOE
4 allele is a well-recognized
risk factor for Alzheimer disease, and several case-control
studies have described an increased risk for coronary artery disease
(CAD) among
4 carriers, with
44 homozygotes showing an earlier onset of the
disease (3)(4)(5)(6)(7)(8)(9)(10). However, other authors have found a
nonsignificantly increased or even a decreased frequency of the
4 allele among CAD patients
(11)(12). Compared with
33 homozygotes, carriers of the
2 and
4 alleles
showed decreased and increased LDL-cholesterol, respectively
(13). The
2 allele has also been
associated with higher triglyceride concentrations
(14). DNA polymorphisms in the angiotensinogen (AGT), angiotensin receptor type 1 (AT1R), and angiotensin-converting enzyme (ACE) genes have been linked to the risk of developing cardiovascular diseases. Among these polymorphisms, the ACE insertion/deletion (I/D) and the AGT-235M/T polymorphisms have been linked with differences in ACE and angiotensin II (Ang II) concentrations in plasma. Compared with individuals with an ACE-ID/II or AGT-MM/TM genotype, ACE-DD and AGT-TT genotypes have significantly higher concentrations of ACE and angiotensin, respectively (15)(16). The ACE-DD and AGT-TT genotypes have been associated with an increased risk for CAD in some studies, but not others (17)(18)(19). Several metaanalyses have investigated the association of the ACE polymorphism with myocardial infarction (MI). Whereas some authors found evidence for an association between the DD genotype and MI, others failed to confirm this result and suggested a bias toward publishing positive associations (20)(21)(22).
There is growing evidence of an interaction between the renin-angiotensin system and hypercholesterolemia in the risk for hypertension and atherosclerosis. Hypercholesterolemia induces vascular expression of AT1R in rabbits (23)(24), and ACE inhibitors and AT1R antagonists attenuate atherogenesis in hyperlipidemic rabbits and APOE-deficient mice, an animal model of atherosclerosis (25)(26). In addition, Ang II stimulates cholesterol biosynthesis in macrophages, an effect mediated by increased expression of hydroxymethylglutaryl (HMG)-CoA reductase (27).
To determine whether variations in the APOE, AGT, AT1R, and ACE genes contribute to the risk for early MI, we genotyped 220 Spanish male MI patients and 200 healthy controls younger than 55 years. The relationships between the genotypes and several clinical and biochemical markers were also analyzed.
| Materials and Methods |
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We also recruited 200 male healthy controls (hospital staff, eligible residents, and blood donors; mean age, 42 ± 6 years; range, 2155 years), who were matched with patients for age and ethnicity. Although blood pressure was not measured in these controls, they did not have cardiovascular disease or diabetes. None of the controls was using lipid-lowering or antihypertensive drugs. All patients and controls were residents in the region of Asturias (Northern Spain; total population, 1 million) and gave their consent to participate in the study. This study was approved by the Ethical Committee of Hospital Central Asturias.
apoe genotyping
Genomic DNA (100 ng) was PCR-amplified in a final volume of
30 µL containing 30 pmol of each primer
(5'-TCCAAGGAGCTGCAGGCGGCGCA-3' and
5'-ACAGAATTCGCCCCGGCCTGGTACACTGCCA-3'), 2 mmol/L each dNTP, 2
mmol/L MgCl2, 1x Taq polymerase buffer, 100
mL/L deionized formamide, and 1 U of Taq DNA-polymerase. PCR
consisted of 30 cycles of 95 °C for 30 s, 62 °C for 1 min, and
75 °C for 30 s, followed by a final extension of 5 min at 72 °C.
A 20-µL aliquot of each reaction was digested with 20 U of
HhaI and electrophoresed on a 4% agarose gel. Restriction
digestion fragments were stained with ethidium bromide and
photographed. The APOE alleles were identified as described
previously (2).
agt, at1r, and ace
genotyping
A C-to-T change in the AGT gene produces a
polymorphism at amino acid 235 (M235T). To analyze this polymorphism,
we PCR-amplified genomic DNA with primers 5'-GATGCGCACAAGGTCCTG-3'
and 5'-CAGGGTGCTGTCCACACTGGCTCGC-3' (annealing at 62 °C).
Reactions were digested with the restriction enzyme BstUI
and electrophoresed on a 3% agarose gel. Alleles were visualized as
fragments of 303 bp (allele M) and 279 bp (allele T).
The 1166 A/C polymorphism in the 3' region of the AT1R gene and the 287-bp insertion/deletion (I/D) polymorphism in the ACE gene were analyzed as described previously (29). Each DD genotype was confirmed through a second PCR with primers specific for the insertion sequence (30).
statistical analysis
Differences of allele and genotype frequencies were compared using
the
2 test. Odds ratios and their 95%
confidence intervals were also calculated. The Student
t-test was used to compare two means, and ANOVA was
used when more than two groups were compared. A P value
<0.05 indicated a statistically significant effect. For the
statistical analysis, we used the computer program BMDP-New Systems
(BMDP Statistical Software).
| Results |
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The APOE, AGT, AT1R, and
ACE genotype frequencies are summarized in Table 2
. In our population, the APOE
4 allele and genotype frequencies were similar
between patients and controls. AGT, ACE, and
AT1R allele and genotype frequencies did not differ between
patients and controls. Mean biochemical values did not differ between
the genotypes of each of the four polymorphisms in patients or controls
(Table 2
).
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APOE, AGT, AT1R, and ACE
allele and genotype frequencies did not differ between patients with or
without diabetes, or with or without hypertension (data not shown). We
analyzed a possible synergistic effect between the APOE and
the AGT, AT1R, and ACE polymorphisms.
The APOE genotype did not modify the risk associated with
the ACE or AT1R genotypes (Table 3
). However, the frequency of carriers of the APOE
4 allele was significantly higher among the
AGT-TT patients compared with the
TM/MM patients (P <0.00001).
The frequency of AGT-TT + APOE
4 carriers was significantly higher in the
overall patient group compared with controls [24 of 220 (11%) vs 7 of
200 (3.5%); P = 0.0037; Table 3
]. Thus,
34/44 + AGT-TT
individuals would have an almost fourfold higher risk of suffering an
early episode of MI (odds ratio, 3.38; 95% confidence
interval, 1.58.17).
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Mean cholesterol concentrations were significantly higher in
TT +
44/34 patients
(n = 24; 2480 mg/L) compared with the
TM/MM +
44/34/24 or
TT +
33/23 genotypes
(n = 196; 2160 mg/L; P = 0.029; Table 4
). A total of 94 patients had a total cholesterol (TC) value
higher than the mean value (2200 mg/L), and 14 (15%) were
TT +
34/44, compared
with only 10 of the 126 (8%) with a TC value below the mean
(P = 0.012). Among the controls, the mean TC value was
not significantly higher in those with the TT +
34/44/24 genotype
(n = 7) compared with the other genotypes (n = 193; 2250
± 500 vs 2040 ± 400 mg/L; P = 0.07).
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| Discussion |
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4
allele. This result is in agreement with previous reports that showed
the lowest frequency for the
4 allele in
Southern European populations (31)(32)(33)(34)(35). The role of
APOE genotype in the risk of CAD has been analyzed
previously (4)(5)(6)(7)(8)(9)(10)(11)(12)(36)(37)(38). For the
4 allele, a significantly increased frequency
in patients compared with healthy controls has been described in some
studies, but not others. These discrepancies could be partly
attributable to the fact that these studies analyzed different
populations worldwide and that the
4 allele
could be a risk factor when associated with other genetic or
environmental factors. This allele has been associated with increased
LDL-cholesterol in response to dietary fat
(13)(38)(39)(40). It is thus possible that the
influence of the APOE
4 allele as a
risk factor for MI is limited to populations that consume a high-fat
diet. According to previous results, AGT-235TT and ACE-DD individuals have increased plasma concentrations of angiotensin and ACE, respectively (15)(16). These genotypes have been associated with a higher CAD risk (17)(18)(19). However, only the DD genotype was associated with a slight, nonsignificant increased risk of developing early MI in our population. We had previously described a synergistic effect between the ACE-DD and AT1R-CC genotypes in the risk for early CAD (29).
We also investigated a synergistic effect between the APOE
and the AGT, AT1R, and ACE
polymorphisms. According to our results, the APOE
4 allele increased the risk of suffering an
episode of MI among those with an AGT-TT genotype. The
frequency of AGT-TT +
4 carriers
was higher in the overall patient group compared with controls, and the
frequency of APOE
4 carriers was
higher among patients who were AGT-TT compared with patients
who were TM/MM. Mean cholesterol was
significantly higher in patients who were AGT-TT +
4 carriers than in patients who were
4 carriers + TM/MM or
33/23 + TT. Taken
together, these data suggest that individuals who are
4 carriers + AGT-TT are at an
increased risk of suffering an early episode of CAD, and this
effect could be related to higher cholesterol concentrations.
The published results are variable with respect to the association between polymorphisms of ACE, AGT, AT1R, and APOE with CAD, hypertension, and MI. This variability could be partly attributable to the differences in the risk factors associated with these diseases. In this way, the proportion of smokers may be one important cause for this variability. The patients in our study had MI before the age of 55, and most of them were smokers. Among older patients, lipid disorders may play a more important role. It is very likely that smoking and the associated low HDL-cholesterol concentrations are the primary causes of MI among the patients in this study. Therefore, the synergistic effects of the polymorphisms at the AGT and APOE genes are likely modulating the effects of smoking on hypertension (AGT) and cholesterol (APOE) concentrations.
The existence of a synergistic effect between the AGT and APOE genotypes is in agreement with recent findings that described an interaction between lipid metabolism and the renin-angiotensin system in cardiovascular pathophysiology. Recently, Keidar et al. (27) showed that Ang II injected intraperitoneally into APOE-deficient mice increased the atherosclerotic lesion area, and peritoneal macrophages showed an increased rate of cholesterol biosynthesis mediated by an increased expression of HMG-CoA reductase. This would lead to macrophage cholesterol accumulation and foam cell formation, a major early event in the development of atherosclerosis. The stimulatory effect of Ang II on HMG-CoA reductase concentrations and cholesterol synthesis in APOE-deficient mice was blocked by treatment with losartan, an AT1R blocker (27). Losartan also had an antiatherogenic effect in non-human primates with diet-induced hypercholesterolemia (41). Endothelial dysfunction was greatly improved in hypercholesterolemic men treated with ACE inhibitors, and a reduction in aortic cholesterol content in cholesterol-fed rabbits treated with the ACE inhibitor enalapril has been reported (42)(43). Statins down-regulate AT1R expression in hypercholesterolemic men, a fact that could in part explain the beneficial effect of these drugs (44). Patients with familial hypercholesterolemia and a DD genotype would have an increased risk of CAD (45).
Our work has several limitations, some of which are inherent to case-control studies. The study was based on MI patients from a small region, and all of the patients were male and younger than 55 years. The sample was therefore small. However, the frequencies for the four polymorphisms were in the Hardy-Weinberg equilibrium, suggesting the absence of population biases. Finally, if studies based on other populations confirm our results, genotyping of APOE and AGT polymorphisms could identify individuals at a higher risk of developing MI.
| Acknowledgments |
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| Footnotes |
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| References |
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2 and
4 alleles in patients with ischemic heart disease. Clin Genet 1989;36:183-188.[Web of Science][Medline]
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