Gene Polymorphism but not Catalytic Activity of Angiotensin I–Converting Enzyme Is Associated With Coronary Artery Disease and Myocardial Infarction in Low-Risk Patients
Background An insertion/deletion (I/D) polymorphism of the angiotensin I–converting enzyme (ACE) gene has been postulated to be associated with an increased risk of coronary artery disease (CAD) and myocardial infarction (MI).
Methods and Results In the present study, the effects of I/D gene polymorphism and of ACE activity on CAD and MI were investigated in 920 individuals who underwent coronary angiography for diagnostic purposes. In the total population and in all CAD and MI groups, a strong association was observed between the gene polymorphism and ACE activities; DD genotypes had approximately twofold higher ACE activities than II genotypes. Although classic risk and protective factors of CAD and MI were identified, associations of ACE genotype and of ACE activity to CAD and MI were not detected in the total population. Among subjects defined to be at lower risk of MI by low body mass index and low cigarette consumption, however, an association of the DD genotype with MI was found. Exclusion of individuals with triglyceride levels >140 mg/dL and cholesterol levels >180 mg/dL revealed an association of the DD genotype with CAD. An association of the ACE activity with CAD or MI could not be demonstrated in any of the low-risk populations.
Conclusions Increased ACE activity obviously is not a risk factor of CAD or MI. The importance of the deletion polymorphism for the development of CAD and MI may be restricted to individuals without classic risk factors.
It has been shown that a gene deletion polymorphism of the ACE gene in intron 16 has been reported to be associated with an increased risk of MI.1 2 3 Studies on its association with CAD revealed controversial results.3 4 5
The contributions of the gene deletion polymorphism and ACE activity to the pathogenesis of CAD and MI have not been studied in a large population of individuals whose coronary anatomy was exactly defined by means of coronary angiography. Therefore, it was the aim of the present study to evaluate the association not only of the ACE gene polymorphism but also of ACE activity with CAD and MI in individuals who underwent coronary angiography for diagnostic purposes.
Gene deletion/insertion polymorphism of the ACE gene was analyzed in 920 white male individuals undergoing coronary angiography for diagnostic purposes. Coronary angiography was performed by the Judkins method. Coronary vessels with at least 50% stenosis were defined as diseased. The GS was calculated as described.6 Angina pectoris and acute MI were diagnosed according to conventional criteria. Mean age was 62±9 years in control subjects (n=470) and 63±9 years in patients with MI (n=450). By means of coronary angiography, the study population could be divided into subjects without detectable CAD (n=80; mean age, 57±10 years), patients with coronary arterial stenoses <50% (n=107, 59±10 years), and CAD patients with single-vessel disease (n=139, 62±9 years), double-vessel disease (n=215, 63±9 years), and triple-vessel disease (n=379, 63±9 years). Control group 1 (n=80) consisted of 32 patients whose coronary anatomy was evaluated for valvular surgery and 48 control subjects who were suspected to have CAD but in whom cardiac diseases were excluded by coronary angiography and other diagnostic interventions. Because the DD genotype has been postulated to be associated with ischemic and idiopathic dilated cardiomyopathy,7 persons with this disorder did not participate in this investigation and therefore were not included in our study population of 920 subjects. Also, patients who received ACE inhibitor medication for >3 months did not participate in the present study because therapy with ACE antagonists could influence the progression of CAD and the development of MI.8
Measurements of Serum Enzymes and Substrates and Definitions of Variables
Total cholesterol, apoB, apoA1, and lipoprotein (a) [Lp(a)] were measured by conventional methods of clinical chemistry. Serum ACE activity was measured in duplicate by a colorimetric method.9 Because serum ACE activity is affected by a number of ACE inhibitor medications, the activity of this enzyme was measured only in sera of patients without ACE antagonist therapy (n=769).
Detection of Insertion/Deletion Polymorphism of the ACE Gene
Leukocyte DNA was amplified according to Reference 10. Amplified DNA was electrophoresed in 2% agarose gels and visualized by ethidium bromide staining. The polymorphism of the amplified ACE gene was demonstrated in agarose gels by the presence of a 490-bp fragment (insertion polymorphism, I allele) or of a 190-bp fragment (deletion polymorphism, D allele). Potential mistyping of I/D heterozygotes was controlled according to Lindpaintner et al.5
Data presented are mean±SD. Distribution of parameters was checked by the Kolmogorov-Smirnov goodness-of-fit test. Since BMI, apoB, apoA1, Lp(a), GS, and ACE activity were not distributed normally, predominantly nonparametric tests had to be applied. The effects of variables on MI were tested by multiple logistic regression and by Kruskal-Wallis one-way ANOVA. The effects on CAD (defined by the degree of vessel disease and by the GS6 ) were estimated by Kruskal-Wallis one-way ANOVA. The correlation between ACE activity and age was tested by multiple regression analysis.
Relation of Established Risk Factors and of ACE Genotype to MI and CAD
Total cholesterol, triglycerides, apoB, apoA1, Lp(a), prevalence of arterial hypertension, BMI, and cigarette consumption were not different between the ACE genotypes of the total study population and of each subgroup (not shown).
Whereas triglycerides (P<.05), cholesterol (P<.05), apoB (P<.05), diabetes mellitus (P<.05), and cigarette consumption (P<.05) were identified as risk factors of MI and apoA1 (P<.05) as a protective factor against MI, no association was found between the ACE I/D genotype and risk of MI (Table⇓). Although in the present study population, age at first MI ranged from 32 to 86 years, subjects with the DD genotype did not suffer their first MI at younger ages than persons with the ID or II genotype either in the total population (II, 57.6±10 years; ID, 56.6±9 years; and DD, 56.7±10 years) or in low-risk groups (not shown). However, among subjects defined to be at lower risk of MI by low BMI (<25 kg/m2) and low cigarette consumption (<5 pack-years), a significant association of the ACE DD genotype with MI was found (P<.02). Exclusion of subjects with hypertension and BMI <25 kg/m2 revealed an association of DD with MI (P<.05).
Levels of triglyceride (P<.01), cholesterol (P<.05), apoB (P<.001), and Lp(a) (P<.01) as well as diabetes mellitus (P<.0001), hypertension (P<.01), and cigarette consumption (P<.001) were demonstrated to be risk factors for CAD, and apoA1 (P<.01) was demonstrated to be a protective factor against CAD. In contrast, the I and D allele frequencies were not only similar between healthy persons and patients with CAD but also did not exhibit any significant differences among patients with single-, double-, or triple-vessel disease (Table⇑). In addition, the GSs of II, ID, and DD genotype subjects were essentially the same in the total population and in each CAD or MI group (Fig 1⇓). However, among subjects at lower risk of CAD (levels of triglycerides <140 mg/dL and cholesterol <180 mg/dL), a significant association of the ACE DD genotype with CAD was found (degree of vessel disease, P<.01; GS, P<.002).
Relation of ACE Activity to MI and CAD
A strong association between ACE gene polymorphism and enzymatic activity was observed not only in the total study population (P<.0001; II genotype, 20.7±13.2 IU/mL; ID genotype, 27.8±17.4 IU/mL; DD genotype, 38.3±20.8) but also in all CAD and MI groups (Fig 2⇓). An interaction of ACE activity with age was not observed either in the total study population (r=.002, P=.96) or in the subgroups of control subjects (r=.01, P=.83) and MI patients (r=.01, P=.86).
A significant difference in ACE activities between control subjects and MI patients was not observed (P=.73; II genotype, P=.49; ID genotype, P=.68; DD genotype, P=.52) either in the total population (Fig 2⇑) or in low-risk groups (not shown).
An association of ACE activity with CAD was not detected either in the total population (degree of vessel disease, P=.89; GS, P=.83) or in groups of II genotype subjects (degree of vessel disease, P=.63; GS, P=.28), ID genotype subjects (degree of vessel disease, P=.66; GS, P=.66), and DD genotype subjects (degree of vessel disease, P=.53; GS, P=.23) (Fig 3). Also, no interaction of ACE activity with CAD was observed in low-risk groups (not shown).
Cambien et al1 were the first to report on an association of gene deletion polymorphism with an increased risk of MI. The results of the present study demonstrate that in the total population gene deletion polymorphism of the ACE gene was not associated with an increased risk for MI. These results are in line with those of Cambien and colleagues,11 who reported that ACE gene I/D polymorphism was only weakly associated with MI in the whole population. Furthermore, not only in Cambien et al1 but also in our study, an association of the DD genotype to an increased risk for MI was found in low-risk groups. In contrast to the findings of Cambien et al, we did not detect an association in low-risk patients defined by apoB <1.25 g/L and BMI <26 kg/m2.
The findings of Cambien et al11 suggest that increased ACE activity may be an independent risk factor for MI in subjects younger than age 55 years. In contrast, in our investigation, an association of ACE activity to MI was not found clearly either in young or in old patients. Reasons for these discrepancies are not known.
Studies on the association of gene deletion polymorphism with CAD revealed controversial results. It was reported in a rather small population of individuals (n=245) that the DD genotype was more closely associated with CAD compared with ID and II genotypes.2 In other studies3 4 5 and the present investigation, an association of the ACE I/D genotype with CAD in the total population was not observed. Similar to the report of Mattu et al,4 in the present study the DD genotype was associated with CAD only in low-risk patients.
Potential interactions of ACE activity with CAD have not been investigated yet. The present results clearly demonstrate that ACE activity in healthy persons without CAD and in patients with single-vessel or multivessel disease was essentially the same. This conclusion can be drawn for subjects with II, ID, or DD genotypes.
In general, the results of the present study and of published investigations allow the assumption that the importance of gene deletion polymorphism may be restricted to individuals without classic risk factors. Indeed, it is a common observation that there is a population of patients who develop CAD and MI without having classic risk factors. The identification of the deletion polymorphism in these individuals, and possibly of other polymorphisms, such as the A/C polymorphism of the angiotensin II type 1 receptor gene,12 may be important for primary or secondary prevention of CAD and MI.
Selected Abbreviations and Acronyms
|ACE||=||angiotensin I–converting enzyme|
|apoA1, apoB||=||apolipoprotein A1, apolipoprotein B|
|BMI||=||body mass index|
|CAD||=||coronary artery disease|
The authors gratefully acknowledge the excellent technical assistance of Monika Fink.
- Received July 20, 1995.
- Revision received September 11, 1995.
- Accepted September 21, 1995.
- Copyright © 1995 by American Heart Association
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