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The renin angiotensin system plays an important role in the development of pulmonary artery remodeling and right ventricular hypertrophy in hypoxia-induced pulmonary hypertension as may occur in patients with COPD. Several polymorphisms of genes encoding for components of the renin
angiotensin system such as the M235T polymorphism in the angiotensinogen gene, the 287-base-pair insertion (I)/deletion (D) polymorphism at intron 16 of the ACE gene, and the A1166C polymorphism
in the angiotensin II type 1 receptor gene have been associated with an increased risk of cardiovascular diseases. With respect to the pulmonary circulation, only limited data exist on possible associations between polymorphisms of these genes and pulmonary hypertension and/or right ventricular
hypertrophy. The objective of the present study was to investigate a possible relationship between
polymorphisms of the renin angiotensin system and electrocardiographic evidence of right ventricular hypertrophy in patients with COPD. We therefore determined the angiotensinogen (M235T), angiotensin converting enzyme (I/D), and angiotensin II type 1 receptor (A1166C) genotypes in 87 patients with severe COPD and correlated these data with electrocardiographic parameters of right
ventricular hypertrophy. Thirty-one patients (36%) of 87 patients with COPD showed electrocardiographic evidence of right ventricular hypertrophy. In the male, but not in the female, subgroup, the
angiotensin-converting enzyme DD genotype was negatively associated with electrocardiographic evidence of right ventricular hypertrophy (male: 
2 = 3.8, p = 0.05; female: 2 = 0.05, p = 0.82). We
found no associations between the investigated polymorphisms in the angiotensinogen and angiotensin II type 1 receptor genes and electrocardiographic evidence of right ventricular hypertrophy.
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INTRODUCTION |
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ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
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The development of pulmonary hypertension in patients with chronic obstructive pulmonary disease (COPD) is associated with hypoxia-induced pulmonary vasoconstriction and pulmonary vascular remodeling (1). Recent studies suggest that the renin angiotensin system plays an important role in the development of both pulmonary artery remodeling and right ventricular hypertrophy in hypoxia-induced pulmonary hypertension. In rats, angiotensin-converting enzyme (ACE) expression is increased in the walls of small pulmonary arteries and in the right ventricle during the development of hypoxia-induced pulmonary hypertension (2, 3). Moreover, in several animal models of hypoxia-induced pulmonary hypertension ACE inhibitors and angiotensin II type 1 receptor (AGT1R) antagonists attenuate or prevent the development of structural pulmonary artery changes and right ventricular hypertrophy (4). In patients with COPD most investigators report a significantly higher serum ACE activity and plasma renin activity than in normoxic-normocapnic subjects (8, 9). Plasma ACE levels are also known to be elevated in subjects homozygous for the deletion allele (DD) of the ACE gene compared with heterozygotes (ID) or subjects homozygous for the insertion (II) allele (10, 11). The ACE DD genotype has been associated with a variety of cardiovascular diseases such as left ventricular hypertrophy, increased risk of myocardial infarction, cardiomyopathy, and coronary artery disease (11). Also, polymorphisms in other genes of the renin angiotensin system such as the M235T polymorphism in the angiotensinogen (AGT) gene and the A1166C polymorphism in the angiotensin II type 1 receptor (AGT1R) gene have been associated with cardiovascular disease such as essential hypertension, coronary heart disease, and myocardial infarction (16). With respect to the pulmonary circulation, only limited data exist about an association between pulmonary hypertension, right ventricular hypertrophy, right ventricular function, and polymorphisms of the renin angiotensin system. One study reports that the ACE DD genotype is more prevalent in patients with primary pulmonary hypertension than the non-DD genotype (21). Although the degree of pulmonary hypertension was comparable, patients with the ACE DD genotype had a preserved cardiac output, a lower pulmonary vascular resistance, and lower right atrial pressures than did patients with the non-ACE DD genotype. This finding caused the investigators to suggest that the ACE DD genotype may permit the development of more extensive adaptive right ventricular hypertrophy in patients with primary pulmonary hypertension and may be seen as a marker of maintained right ventricular function. Associations between the M235T polymorphism of the angiotensinogen gene or the A1166C polymorphism of the angiotensin II type 1 receptor gene and pulmonary hypertension have not been described. Also the extent to which these polymorphisms may contribute to the development of right ventricular hypertrophy in patients with COPD is unknown. Therefore we determined the distribution of polymorphisms of the ACE gene (I/ D), AGT1R gene (A1166C), and AGT gene (M235T) in patients with severe stable COPD and correlated these data with electrocardiographic parameters of right ventricular hypertrophy. In analogy with the findings of Abraham and coworkers (21) and data derived from the systemic circulation we hypothesized that, also in patients with COPD, the ACE DD, AGT1R CC, and the AGT TT genotype were positively correlated with right ventricular hypertrophy.
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INTRODUCTION
METHODS
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DISCUSSION
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Study Population
The study group consisted of 87 patients with COPD (62 male, 25 female), ranging from 46 to 79 yr of age (mean, 65 yr), who were admitted to the pulmonary rehabilitation centre Hornerheide (Horn, The Netherlands). COPD was diagnosed in all patients according to the criteria of the American Thoracic Society (22), and FEV1 was expressed as a percentage of the reference values (FEV1% pred) < 70% (23). All patients were stable at the time of the study. Patients with electrocardiographic evidence of severe left ventricular hypertrophy and/or myocardial infarction and patients with signs of left ventricular heart failure and/or heart murmers on physical examination were excluded. The research program was approved by the local ethical committee, and informed consent was obtained from all patients.
Control Group
The control group consisted of 95 subjects (42 male, 53 female) 41 to 70 yr of age (mean, 50 yr). They had no clinical history of COPD and a FEV1% pred within normal limits (mean FEV1% pred, 93%; SD, 8) and were, as the study group, all Caucasians and living in the same region.
Pulmonary Function and Blood Gas Studies
FEV1 was measured, using the pneumotachograph (Masterlab; Jaeger, Würzburg, Germany). Values were expressed as a percentage of reference values. For arterial blood gas analysis blood was obtained by puncture of the radial artery while patients breathed room air. The PaO2, PaCO2, and SaO2 were measured using a blood gas analyzer (ABL 330; Radiometer, Copenhagen, Denmark).
Electrocardiography
To assess the presence of right ventricular hypertrophy a 12-lead electrocardiogram (ECG) was made. The following ECG criteria of right ventricular hypertrophy were used: (1) Incomplete or complete right bundle branch block. (2) Right axis deviation, defined as a frontal plane QRS axis of > 90 degrees. (3) P wave in lead V1, II, or III of > 2.5 mm (P pulmonale). (4) S wave of > 1.5 mm in lead I in combination with a slow R progression. (5) Clockwise rotation of the heart in the horizontal axis defined as a shift in the transition zone to V5 or beyond. (6) Low voltage QRS complex of < 5 mm in all the limb leads (II, III, and AVF).
The ECGs were evaluated by two cardiologists (PvP and EC). In all patients agreement was reached. A positive ECG diagnosis suggestive for right ventricular hypertrophy was accepted if two or more ECG criteria were present (24).
Extraction and Amplification of Genomic DNA
Genomic DNA was extracted from peripheral blood leukocytes with the QIAmp Blood Kit (QIAGEN Inc., Chatsworth, CA).
ACE polymorphism. The ACE genotype was determined by the polymerase chain reaction (PCR) and subsequent gel electrophoresis of the PCR products using the method described by Rigat and colleagues (25). All DD genotypes were subjected to a second, independent PCR amplification to avoid mistyping in ID heterozygote subjects in which the I allele is sometimes suppressed (26). This second PCR did not identify any mistyping.
AGT1R polymorphism. The A1166C polymorphism was determined by PCR amplification of genomic DNA according to the method described by Bonnardeaux and colleagues (18).
AGT polymorphism. The M235T variant was analyzed after PCR amplification of genomic DNA and restriction digestion with Tth 111 I as described by Russ and colleagues (27).
Statistical Analysis
Differences in genotype distributions between patients with COPD
with and without electrocardiographic evidence of right ventricular hypertrophy were tested by the chi-square test (2). Means of variables potentially related to the development of right ventricular hypertrophy were compared by two-sample t test. Statistical significance
was defined at p < 0.05 (28). The Statistical Package for Social Sciences (release 7.5; SPSS Inc., Chicago, IL) was used for statistical analyses.
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Pulmonary Function Test and Blood Gas Analysis
The mean FEV1 (% pred) was 37% (range, 16 to 70%). The mean PaCO2 and PaO2 were 5.7 kPa (range, 4.1 to 8.7) and 9.3 kPa (range, 6.3 to 12.7), respectively. The mean SaO2 was 93.3% (range, 80 to 98%).
Hematocrit and Age
The mean Ht was 43.3% (range, 33 to 52%). The mean age was 65 yr (range, 46 to 79 yr).
Medication
Patients receiving antihypertensive drug treatment (ACE inhibitors [n = 8], angiotensin II receptor blockers [n = 1], or calcium antagonists [n = 10]) were equally distributed over the different genotypes and patients with or without right ventricular hypertrophy.
Electrocardiographic Evidence of Right Ventricular Hypertrophy
Thirty-one patients (36%) of the entire study group of 87 patients had electrocardiographic evidence of right ventricular hypertrophy. Fourteen patients (16%) showed two criteria, nine patients (10%) showed three criteria, five patients (6%) showed four criteria, and three patients (4%) showed five criteria of right ventricular hypertrophy.
Frequencies of RAS Genotypes in the Study Group
The distribution of the DD, ID, and II genotypes of the angiotensin-converting enzyme gene was 32, 49, and 19%, respectively. The distribution of the AA, AC, and CC genotypes of the angiotensin type 1 receptor gene was 53, 37, and 10%, respectively, and the distribution of the MM, MT, and TT genotypes of the angiotensinogen gene was 33, 49, and 18%, respectively.
Frequencies of RAS Genotypes in the Control Group
The distribution of the DD, ID, and II genotypes of the angiotensin-converting enzyme gene was 29, 53, and 18%. The distribution of the AA, AC, and CC genotypes of the angiotensin type 1 receptor gene was 42, 49, and 9%, respectively, and the distribution of the MM, MT, and TT genotypes of the angiotensinogen gene was 33, 48, and 19%, respectively. These percentages did not significantly differ from patients with COPD (p = 0.96, 0.33, and 0.97, respectively). Separate analysis of frequencies of RAS genotypes in male and female subgroups in the study group and the control group did not significantly differ either (data not shown).
Associations between the ACE Genotypes and Right Ventricular Hypertrophy
In the male subgroup, the ACE DD genotype was negatively
associated with electrocardiographic evidence of right ventricular hypertrophy (2 = 3.8; odds ratio, 2.2; 95% confidence interval, 0.8 to 5.5; p = 0.05) (Table 1). In the female subgroup
there was no such association (2 = 0.05; odds ratio, 1.1; 95%
confidence interval, 0.2 to 4.8; p = 0.82). There was no association between the presence of the D allele (DD and ID) and
the presence or absence of electrocardiographic evidence of
right ventricular hypertrophy (entire study group: 2 = 0.56, p = 0.45; male: 2 = 0.38, p = 0.53; female: 2 = 0.05, p = 0.82).
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Possible Confounding Variables in ACE I/D Genotype Subgroups
Mean PaCO2, PaO2, and SaO2 were comparable between the different subgroups (for instance, DD versus non-DD: PaCO2 = 5.6 and 5.7 kPa, respectively, PaO2 = 9.1 and 9.3 kPa, respectively) (Table 2). Patients (male and female) with the DD genotype had a significant higher Ht than did patients with the
non-DD genotype (mean, 44.7 and 42.7%, respectively, t = 
2.9, p = 0.004). This was also true in the male subgroup with
the DD genotype (mean, 45.1 and 42.9%, respectively, t = 2.6, p = 0.01). Patients with the D allele (DD and ID) were
significantly younger than the patients with the II genotype
(mean, 64.7 and 67.8 yr, respectively, t = 1.9, p = 0.05) and
had a significantly higher FEV1 (% pred) than did patients
with the II genotype (mean, 38.5 and 31.7%, respectively, t = 2.2, p = 0.03).
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Associations between the AGT1R and AGT Genotypes and Right Ventricular Hypertrophy
We found no significant associations between the investigated polymorphisms in the AGT1R and AGT genes and electrocardiographic evidence of right ventricular hypertrophy, neither for the group as a whole nor for female and male subgroups.
Possible Confounding Variables in AGT1R and AGT Genotype Subgroups
Mean PaCO2, PaO2, and FEV1 (% pred) were comparable between the different subgroups (data not shown). Male patients
with the AGT1R C allele (CC and AC) had a significantly
lower SaO2 and were significantly older than the patients with
the AGT1R AA genotype (mean SaO2, 92.7 and 94.1%, respectively, t = 2.0, p = 0.04 and mean age, 68 and 64 yr, respectively, t = 2.1, p = 0.03). This was also true for the mean age
in the entire group (mean age, 67 and 64 yr, respectively, t = 1.9, p = 0.05).
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DISCUSSION |
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The main finding of this study was a negative association between the ACE DD genotype and electrocardiographic evidence of right ventricular hypertrophy in male patients with COPD. This negative association was in contrast with our hypothesis that stated that the ACE DD genotype would be positively associated with right ventricular hypertrophy. This hypothesis was based on recent findings of Abraham and colleagues (21) in patients with pulmonary hypertension that indeed showed more extensive adaptive right ventricular hypertrophy. An important difference, however, between those data and our study is that Abraham and coworkers studied patients with primary pulmonary hypertension, whereas we studied patients with COPD who may develop pulmonary hypertension secondary to chronic alveolar hypoxia. The different outcome of the two studies may suggest that the function of the renin angiotensin system differs in primary pulmonary hypertension from that in secondary pulmonary hypertension in COPD. A differential function of the renin angiotensin system was also observed in two different animal models of pulmonary hypertension (7).
Because we realize that the prevalence of right ventricular hypertrophy in patients with COPD increases not only with the severity of airway obstruction but also with several other factors such as age, hypoxemia, CO2 retention, and polycythemia (29, 30), we analyzed the effects of these possible confounding variables on the associations between ACE genotypes and electrocardiographic evidence of right ventricular hypertrophy. The mean PaCO2, PaO2, FEV1 (% pred), SaO2, and age were not significantly different in patients with the DD genotype from those in patients with the non-DD genotype. However, the mean Ht was significantly higher in both the patient group as a whole and in the male subgroup with the DD genotype compared with the non-DD genotype patients (mean, 44.7 and 42.7%; mean, 45.1 and 42.9%, respectively). The higher hematocrit reported for the whole patient group with a DD genotype versus patients with the non-DD genotype may be explained by the higher hematocrit in the male subgroup. Although these mean Ht values are within normal limits and the mean differences are small, the increased Ht could potentially contribute to increased pulmonary arterial pressures in patients with COPD with the DD genotype. However, an increased Ht would be associated with an increased right ventricular hypertrophy. Because we found a negative association between the ACE DD genotype and right ventricular hypertrophy, normalization of the data for Ht would result in an even stronger negative association between the ACE DD genotype and right ventricular hypertrophy. The ACE DD genotype was negatively associated with right ventricular hypertophy, but only in the male patients. Interestingly, the ACE DD genotype was recently found to be a sex-specific candidate gene for systemic hypertension (31), albeit that in that study the ACE DD genotype was positively associated with systemic hypertension.
In female patients no association was found between the DD genotype and electrocardiographic evidence of right ventricular hypertrophy. It is well known that the female sex is a cardioprotective factor, and there is a growing body of evidence that estrogens modulate the development of cardiac hypertrophy (32). Estradiol protects against pulmonary vascular remodeling and right ventricular hypertrophy in male monocrotaline-treated rats (33). Finally, estradiol treatment has been shown to attenuate hypoxia-induced vasoconstriction in lamb lungs (34). We therefore believe that, although most female patients in this study were postmenopausal, estrogens may mask or delay a potential association between the ACE genotype and right ventricular hypertrophy in female patients with COPD.
Patients carrying the D allele (DD and ID) were significantly younger and had a significantly higher FEV1 (% pred) than did patients with the II genotype. Younger age and a higher FEV1 (% pred) could theoretically mean less right ventricular hypertrophy compared with older patients and patients with a lower FEV1 (% pred). In the present study, however, there was no association between the presence of the D allele (DD and ID genotype) and the presence or absence of electrocardiographic evidence of right ventricular hypertrophy.
No significant associations were found between the angiotensin II type 1 receptor (A1166C) and angiotensinogen (M235T) genotypes and electrocardiographic evidence of right ventricular hypertrophy. In the systemic circulation, the angiotensin II type 1 receptor CC genotype and especially the angiotensinogen TT genotype have been associated with essential hypertension (18, 19). The data presented here suggest that these polymorphisms do not significantly contribute to the development of pulmonary hypertension and/or right ventricular hypertrophy in patients with COPD.
In theory, the distribution of RAS genotypes may be different in patients with COPD from that in patients without COPD. However, the distributions of the ACE, AGT1R, and AGT genotypes found in the present study did not significantly differ from those in our control group and those described in control populations of other studies (12, 17, 20). It is therefore unlikely that the negative association between the DD genotype of the ACE gene and electrocardiographic parameters of right ventricular hypertrophy is influenced by differences in ACE genotype distribution in patients with and without COPD. The mean age of the control group was 50 yr (SD, 7), which is indeed lower than the mean age of the COPD group (65 yr; SD, 7). To exclude a possible pre-COPD confounder in the control group we have subanalyzed the data of the control group. Analysis of the RAS genotypes in the older subjects in the control group (mean age, 58 yr; SD, 5; n = 27) did not reveal a significant change in genotype distribution, not when compared with the young subgroup (mean age, 45 yr; SD, 3; n = 68; FEV1% pred = 94%; SD, 7), or when compared with the COPD group. Moreover, mean FEV1% pred in that older subgroup of our control population was 90% (SD, 8), which is not significantly different from the 93% (SD, 8) of the total group, and far above that in the COPD group (37%). Therefore, we think that it is very unlikely that our control group contained a COPD-prone subpopulation.
A limitation of the present study was that evidence of right ventricular hypertrophy was based on electrocardiographic criteria. Although electrocardiography is highly specific for detecting right ventricular hypertrophy in patients with COPD, this technique is rather insensitive (35).
In conclusion, this study has shown a negative association between the ACE DD genotype and electrocardiographic evidence of right ventricular hypertrophy in male patients with COPD. This may indicate that male patients with COPD with the ACE DD genotype have lower mean pulmonary arterial pressures and in theory have a better prognosis than do male patients with the non-DD genotype. On the other hand it could mean that male patients with COPD with the ACE DD genotype show less adaptive right ventricular hypertrophy, which theoretically could mean a worse prognosis when compared with male patients with the non-DD genotype. Further studies, that include hemodynamic and echocardiographic measurements are needed to elucidate whether this negative association is a result of lower mean pulmonary arterial pressures or diminished adaptive right ventricular hypertrophy in these patients. Analysis of polymorphisms of the ACE gene may, in the future, play an important role in the risk assessment and medical management of pulmonary hypertension in male patients with COPD.
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Footnotes |
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Correspondence and requests for reprints should be addressed to Robert J. van Suylen, M.D., Dept. of Pathology, Maastricht University, P.O. Box 5800, 6202 AZ Maastricht, The Netherlands.
(Received in original form July 13, 1998 and in revised form January 12, 1999).
Acknowledgments: The writers thank P. Aarts and A. Bergh for technical assistance.
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References |
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  H. R. Gosker, H.-J. Pennings, and A. M. W. J. Schols ACE Gene Polymorphism in COPD Am. J. Respir. Crit. Care Med., September 1, 2004; 170(5): 572 - 572. [Full Text] [PDF]
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N. S. Hopkinson, A. H. Nickol, J. Payne, E. Hawe, W. D.-C. Man, J. Moxham, H. Montgomery, and M. I. Polkey Angiotensin Converting Enzyme Genotype and Strength in Chronic Obstructive Pulmonary Disease Am. J. Respir. Crit. Care Med., August 15, 2004; 170(4): 395 - 399. [Abstract] [Full Text] [PDF]
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 A.G.N. Agusti, A. Noguera, J. Sauleda, E. Sala, J. Pons, and X. Busquets Systemic effects of chronic obstructive pulmonary disease Eur. Respir. J., February 1, 2003; 21(2): 347 - 360. [Abstract] [Full Text] [PDF]
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A. A. Aldashev, A. S. Sarybaev, A. S. Sydykov, B. B. Kalmyrzaev, E. V. Kim, L. B. Mamanova, R. Maripov, B. K. Kojonazarov, M. M. Mirrakhimov, M. R. Wilkins, et al. Characterization of High-Altitude Pulmonary Hypertension in the Kyrgyz: Association with Angiotensin-Converting Enzyme Genotype Am. J. Respir. Crit. Care Med., November 15, 2002; 166(10): 1396 - 1402. [Abstract] [Full Text] [PDF]
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R. J. van SUYLEN, W. M. AARTSEN, J. F. M. SMITS, and M. J. A. P. DAEMEN Dissociation of Pulmonary Vascular Remodeling and Right Ventricular Pressure in Tissue Angiotensin-converting Enzyme-deficient Mice Under Conditions of Chronic Alveolar Hypoxia Am. J. Respir. Crit. Care Med., April 1, 2001; 163(5): 1241 - 1245. [Abstract] [Full Text]
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M.A. Higham, D. Dawson, J. Joshi, P. Nihoyannopoulos, and N.W. Morrell Utility of echocardiography in assessment of pulmonary hypertension secondary to COPD Eur. Respir. J., March 1, 2001; 17(3): 350 - 355. [Abstract] [Full Text] [PDF]
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