Antihypertensive treatment efficacy: genetic aspects




J. J. BRUGTS,MD, PhD, MSc

M. L. SIMOONS,MD, PhD
Department of Cardiology
Erasmus MC Thorax Center
Rotterdam, THE NETHERLANDS

by J . J . Brugt s and M. L . Simoons ,The Netherlands

Angiotensin-converting enzyme (ACE) inhibitors are among the most commonly used drugs in stable coronary artery disease (CAD), as these agents have been proven effective in reducing the risk of cardiovascular morbidity and mortality. As with other drugs, individual variation in treatment benefit is likely. Such heterogeneity could be used to target ACE inhibitor therapy in those patients most likely to benefit from treatment. However, prior attempts to target ACE inhibitor therapy at the patients most likely to benefit from such prophylactic treatment in secondary prevention based on clinical characteristics or the level of baseline risk have not been satisfactory. A new “tailored-therapy” approach would integratemore patient-specific characteristics, such as genetic information (DNA). Pharmacogenetic research of ACE inhibitors in CAD patients is at a formative stage, and studies are limited. The PERGENE (PERindopril GENEtic association) study is a large pharmacogenetic substudy of the randomized placebo-controlled EUROPA (EUropean trial on Reduction Of cardiac events with Perindopril in stable coronary Artery disease) trial, which aims to assess the feasibility of pharmacogenetic profiling with the ACE inhibitor perindopril.

Medicographia. 2010;32:302-308 (see French abstract on page 308)

Angiotensin-converting enzyme inhibitors

Angiotensin-converting enzyme (ACE) inhibitors competitively block the conversion of angiotensin I into angiotensin II. This blockade results in a decrease in circulating and local levels of angiotensin II, thereby inhibiting the main effects of angiotensin II: arteriolar vasoconstriction and water and salt retention. However, ACE inhibitors do not antagonize the AT1 receptor and thus do not inhibit the unfavorable effects of angiotensin II completely. Furthermore, the formation of angiotensin II is restored, at least partially, due to the reactive rise that occurs when renin release is blocked by angiotensin II–induced negative feedback. A second beneficial effect of ACE inhibitors, and a main difference between them and angiotensin receptor antagonists, is the increase in bradykinin levels caused by the decrease in transformation of bradykinin into inactive peptides.1,2 The increase in bradykinin levels induced by ACE inhibitors leads to the release of nitric oxide and prostaglandins with vasodilating effects on vessel walls.2,3

The efficacy of ACE inhibitors has been demonstrated by several large clinical trials in patients at high risk of cardiovascular disease, including those with a left ventricular ejection fraction of <40% after myocardial infarction (MI), heart failure (HF), or a history of cerebrovascular accidents, and in those at a lower risk of cardiovascular events, in particular patients with stable coronary artery disease (CAD) without overt HF.4-10 Nowadays, the use of ACE inhibitors is recommended in guidelines on the management of hypertension, stable CAD, MI, and HF and on the prevention of renal insufficiency progression in diabetes mellitus–related kidney disease.11-13 In particular, ACE inhibitors are recommended as a secondary prevention treatment for the broad group of patients with known CAD.11 This review primarily focuses on patients with stable CAD and the ACE inhibitor perindopril, as studied in EUROPA (EURopean trial On reduction of cardiac events with Perindopril in patients with stable coronary Artery disease).10,14

Figure 1
Figure 1. Treatment benefit of perindopril on primary end point and selected secondary end points in the EUROPA trial.

Size of squares proportional to number of patients in that group. Dashed line indicates overall relative risk.
Abbreviations: EUROPA, EUropean trial on Reduction Of cardiac events with Perindopril in stable coronary Artery disease; MI, myocardial infarction; UA, unstable angina.
Modified from reference 10: Fox and The European Trial on Reduction of Cardiac Events with Perindopril in Patients with Stable Coronary Artery Disease Investigators.
Lancet. 2003;362:782-788. © 2003, Elsevier Ltd.

The EUROPA trial

EUROPA studied the ACE inhibitor perindopril in a population with stable CAD without HF.10 In this trial, 12 218 patients were randomly assigned perindopril 8 mg once daily (n=6110) or matching placebo (n=6108). The primary end point was cardiovascularmortality,MI, or cardiac arrest. Themean age of patients was 60 years, 85% were male, and 92% were taking platelet inhibitors, 62% β-blockers, and 58% statins. During a mean follow-up of 4.2 years, perindopril was associated with a 20% relative reduction in the primary end point, from 9.9% to 8.0%, (hazard ratio [HR], 0.80; 95%confidence interval [CI], 0.71 to 0.91; 8% vs 10%) (Figure 1).10 These benefits were consistent in all clinical subgroups across several secondary end points and independent of baseline blood pressure (BP) and use of concomitant medication. Perindopril was safe and well tolerated. To prevent one major cardiovascular event, 50 patients with stable CAD needed to be treated for a period of 4.2 years.10 Several substudies of EUROPA have established that ACE inhibitors exert additional beneficial effects by improving endothelial function and neurohumoral balance and by reducing unfavorable remodeling of the coronary arteries.15-18

Prior attempts to direct ACE inhibitor therapy toward those patients most likely to benefit

Several analyses have been performed to test the consistency of the treatment benefit of ACE inhibitors in patient subgroups based on clinical characteristics.19-23 Heterogeneity in the clinical treatment effect of ACE inhibitors could be used to direct ACE inhibitor therapy toward those patients most likely to benefit from such therapy. Tailored ACE inhibitor therapy would improve patient benefits and reduce unnecessary health-care costs and side effects.

Using EUROPA trial data, a risk model based on baseline clinical characteristics was developed.20 The treatment benefit of perindopril was consistent across different risk categories, and therefore not modified by the level of baseline risk (Figure 2).20 Renal insufficiency is an important risk factor for developing cardiovascular disease.21 To study whether patients with normal renal function or impaired renal function experienced different treatment benefit, a subgroup analysis was performed within the EUROPA trial. This analysis showed that treatment benefit was not modified by renal insufficiency.22

In a recent meta-analysis of the EUROPA, PROGRESS (Perindopril pROtection aGainst REcurrent Stroke Study), and ADVANCE (Action in Diabetes and Vascular disease: PreterAx and DiamicroN MR Controlled Evaluation) trials investigating the same ACE inhibitor perindopril, we demonstrated a consistent treatment effect of ACE inhibitor–based regimens independent of clinical characteristics or baseline BP levels.23 Hence, no heterogeneity of treatment benefit was observed according to clinical characteristics. It did not appear feasible to target ACE inhibitor therapy at stable CAD patients in the specific subgroups most likely to benefit from this type of prolonged prophylactic treatment based on simple clinical characteristics.

Pharmacogenetic approach to individualizing ACE inhibitor therapy

As simple clinical patient characteristics are inadequate for tailoring ACE inhibitor therapy, new approaches that integrate more patient-specific characteristics should be considered, such as pharmacogenetic profiling of drug response. The new field of cardiovascular pharmacogenetics, which is expanding rapidly, involves examining the genetic determinants of patients’ responses to drugs. Pharmacogenetics aims to understand why some drugs work better for some people than others and why some people are more likely than others to experience side effects. Indeed, pharmacogenetic profiling could lead to significant advances in individualized cardiovascular medicine.

A priori, several types of factors are expected to play a role in determining the response of a patient to therapy. Genetic factors causing differences in drug absorption and metabolic clearance are highly relevant; however; this is as yet a relatively unexplored field for ACE inhibitors. Better known are the genetic factors affecting the direct pharmacodynamic pathways that ACE inhibitors act on, the renin-angiotensin-aldosterone system (RAAS) and bradykinin pathways. These are likely to impact the clinical efficacy of ACE inhibitors. In recent years, several genetic polymorphisms in RAAS genes have been associated with high BP levels or increased cardiovascular risk.3,24,25 Nearly all prior studies focused on two polymorphisms, the ACE insertion/deletion (I/D) polymorphism and the M235T polymorphism in the angiotensinogen gene. Because of the limited study sample size and power, results have been inconsistent, and these important topics have not yet been investigated convincingly. With regard to the connection between genetic variation and ACE inhibitor treatment response, results are scarce as clinical data are lacking. No prior research with ACE inhibitors in stable CAD has been performed on a large-scale or in a randomized trial setting.

Figure 2
Figure 2. Treatment effect (relative risk reduction) in patients categorized in tertiles
according to 4.2-year risk of cardiovascular mortality and nonfatal MI.

Consistency of the treatment benefit of perindopril in the EUROPA trial using a risk model based on clinical characteristics.
Abbreviations: EUROPA, EUropean trial on Reduction Of cardiac events with Perindopril in stable coronary Artery disease; MI, myocardial infarction.
Modified from reference 20: Deckers et al. Eur Heart J. 2006;27:796-801. © 2006, The European Society of Cardiology.

It has been suggested that the response to drug therapy may be influenced by genetic polymorphisms in different ways. Firstly, pharmacodynamics may be affected by polymorphisms in the genes of all the proteins involved in the RAAS system and related systems, including receptors and signal transduction molecules. Secondly, variations in drug absorption and metabolic clearance may cause interindividual variation in pharmacokinetics. Thirdly, variations within genes of the RAAS system and related systems may influence atherosclerosis (underlying disease process) and inherent differences in the susceptibility to therapeutic agents such as ACE inhibitors.

The concept of using pharmacogenetic research to individualize medicine is emerging rapidly and is clinically highly relevant. Several successes of this approach for different cardiovascular agents have recently been demonstrated, such as the activation of clopidogrel26,27 and the risk of rhabdomyolysis associated with statin therapy.28 Current pharmacogenetic data are often obtained from observational cohort studies or cross-sectional data. Large randomized clinical trials using DNA offer a unique opportunity to study this concept of tailored therapy and to truly test the feasibility of pharmacogenetic profiling of treatment benefit. The objective is to construct a genetic profile that enables doctors to predict the benefit of treatment in a patient in advance. Additionally, pharmacogenetics will teach us more about the individual response mechanism to medications.

Current literature

Three studies have performed a pharmacogenetic analysis of ACE inhibitors or of a treatment regimen containing ACE inhibitors.29-31 Two of them studied only the ACE I/D polymorphism and found no associations,29,30 while one study examined relevant genetic targets within the RAAS and found some interesting results.31

The GENetics of Hypertension-Associated Treatment (GENHAT) study was the first to assess the concept of pharmacogenetics of antihypertensive drugs.29 The investigators used a double-blind, active-controlled randomized trial of antihypertensive treatment that included hypertensives >55 years of age with at least 1 risk factor for cardiovascular disease. The ACE I/D genotype was determined in 37 939 participants randomized to chlorthalidone, amlodipine, lisinopril, or doxazosin treatment and followed up for 4 to 8 years. Primary outcomes included fatal coronary heart disease (CHD) and/or nonfatal MI. Fatal and nonfatal CHD occurred in 3096 individuals during follow-up. The hazard rates for fatal and nonfatal CHD were similar across antihypertensive treatments.

The ACE I/D genotype group was not associated with fatal and nonfatal CHD (relative risk of deletion:deletion (DD) versus insertion:deletion (ID) and insertion:insertion (II), 0.99; 95% CI, 0.91 to 1.07). The 6-year hazard rate for fatal and nonfatal CHD in the DD genotype group was not statistically different from the ID and II genotype groups by type of treatment. Therefore, the authors concluded that ACE I/D genotype group was not a predictor of CHD, nor did it modify the response to antihypertensive treatment. The ACE I/D polymorphism is not a useful marker for predicting antihypertensive treatment response.29 Unfortunately, the authors did not study other relevant candidate genes or multiple genetic polymorphisms within the complex RAAS system.

In PROGRESS,30 the ACE genotype I/D polymorphism was studied via the effect of a perindopril-based BP-lowering regimen on macrovascular events, dementia, and cognitive decline among hypertensive and nonhypertensive patients with a history of cerebrovascular disease. There were no associations between ACE genotypes and cerebrovascular disease history or cardiovascular risk factors, including baseline BP. ACE genotype was not associated with the long-term risks of stroke, cardiac events, mortality, dementia, or cognitive decline; neither did ACE genotype predict BP reduction associated with the use of the ACE inhibitor perindopril. Similarly, there was no evidence that ACE genotype modified the relative benefits of ACE inhibitor–based therapy versus placebo. ACE genotype is not useful for predicting either the risk of disease or the benefits of perindopril-based BP-lowering treatment.30

In the Chinese Community-Based Comprehensive Prevention and Control of Hypertension Project, investigators studied the genetic contribution to variation in BP response to ACE inhibitors.31 Fourteen single-nucleotide polymorphisms (SNPs) in the angiotensinogen (AGT), angiotensin receptor 1 (AGTR1), and angiotensin receptor 2 (AGTR2) genes were evaluated for their association with BP response to ACE inhibitor in 1447 Chinese patients with hypertension in a 2-stage, 3-year benazepril postmarket survey. The AGT rs7079 (C/T) SNP (3’-untranslated region) was significantly associated with the response of diastolic blood pressure (DBP) to benazepril (DBP response: 7.4 mm Hg for subjects with the CC genotype 8.9 mm Hg for CA, and 10.1 mm Hg for AA; P<0.001). Although there was no association of individual SNPs in the AGTR1 gene, there was a graded response between common haplotypes and systolic blood pressure (SBP) reduction. Haplotypes are a combination of alleles at different markers along the same chromosome that are inherited as a unit (linkage disequilibrium pattern). The total variations in response to ACE inhibitor therapy explained by the AGT SNP and AGTR1 haplotype groups were 13%for SBP and 9%to 9.6%for DBP, respectively. These findings will be useful in future studies, providing genetic markers to predict hypertensive response to ACE inhibitor therapy.31

An important limitation of prior studies is the investigation of only one or two polymorphisms within one candidate gene, which ignores well-documented feedback mechanisms within the RAAS and also the fact that the two angiotensin II receptors (AT1 and AT2) have counteracting effects. Additionally, ACE I/D polymorphism is not a reflection of the entire RAAS. We suggest that more comprehensive coverage of genetic variation in multiple RAAS genes is needed by using a haplotype approach to study common variations within relevant candidate genes. Combining information from multiple SNPs in the RAAS genes will result in a more comprehensive, in-depth analysis of the RAAS and bradykinin system genes and their relation to ACE inhibitor treatment benefit, which is more likely to unravel any existing pharmacogenetic associations.

The PERGENE study: a new substudy of the EUROPA trial

PERGENE (PERindopril GENEtic association study) is a pharmacogenetic substudy of the main EUROPA trial.32 PERGENE aims to assess the feasibility of pharmacogenetic profiling of the treatment benefit of ACE inhibitors in patients with stable CAD. We hypothesized that genetic polymorphism in the RAAS and kininogen-kallikrein-bradykinin pathways may influence the treatment benefit of ACE inhibitors in patients with stable CAD. Polymorphisms were selected based on haplotype tagging SNPs using the HapMap genome project to comprehensively cover all genetic variation within genes; additional selection was based on functionality, location within the gene (promoter), or relevant literature. The PERGENE study is unique in the field of pharmacogenetic studies because of the large sample size, the randomized placebo-controlled design, and the availability of extensive and accurate phenotypic data. Also, the extensive selection of 52 tagging SNPs in 12 candidate genes in both pathways ensures a new and comprehensive coverage of common genetic variation in candidate genes.

The main outcome measure of PERGENE was the interaction between genetic factors and treatment effect of ACE inhibitors during follow-up. The secondary end points were the relation between genetic determinants and BP and BP reduction and ACE inhibitor therapy. The size of this pharmacogenetic substudy allowed detection with a statistical power of 98% to detect a difference in hazard ratios (treatment effect) of 20% between genotypes with minor allele frequency of 0.20 (two-sided alpha 0.05).

_ Genetic analysis within PERGENE
The DNA samples collected in the EUROPA study offer a unique opportunity to investigate the relations between polymorphisms in genes of the RAAS with the treatment benefit of an ACE inhibitor on cardiovascular events in a sufficiently large population and in a randomized double-blind setting. As mentioned, the available studies of this subject have to date been of small size and nonrandomized, so reported relationships may have been due to chance findings. Furthermore, the majority of studies so far include only one RAAS polymorphismor one RAAS gene. In contrast, PERGENE uses a haplotype-tagging selection procedure to comprehensively cover all common genetic variations (>90%) in the relevant genes within the RAAS and bradykinin pathways. We will use the latest information from HapMap Genome Project, SEATTLE, and other up-to-date genetic information platforms as well as sophisticated software packages, such as Haplostats, for these haplotype analyses.

The determination of haplotypes is essential for understanding genetic variation and the inheritance of complex diseases. An analysis based on haplotypes is more advantageous than an analysis based on individual SNPs, especially in the presence of multiple susceptibility alleles and when linkage disequilibria between SNPs are weak. With a single SNP approach, associations may be missed when the causal SNP is not in linkage disequilibrium with the single analyzed SNP. It is more informative to simultaneously analyze multiple markers in a region of interest that identifies genetic variants underlying various human traits; also, these markers should be selected based on tagging principles and linkage disequilibrium.

By combining information from multiple SNPs in the RAAS and bradykinin pathway genes, a more efficient, comprehensive, in-depth analysis of common genetic variation in relation to ACE inhibitor therapy is performed, which is more likely to unearth important pharmacogenetic associations.

Feasibility of pharmacogenetic profiling of ACE inhibitors

Highly developed pharmacogenetic profiling could increase the overall efficacy of ACE inhibitors and reduce the number of patients treated without any benefit. The concept of ACE inhibitor pharmacogenetic profiling should be investigated further and replicated in similar patient populations, but also in patients at higher risk of cardiovascular events, as stable CAD patients are at relatively low risk. With regard to PERGENE, further replicationmust be sought in other large trials. Additionally, other relevant genetic targets need to be investigated, such as the genes involved in the metabolism of ACE inhibitors, ie, cytochrome P450 genes (pharmacokinetics). However, until now no specific genetic targets for ACE inhibitor metabolism have been discovered. Ultimately, one would wish to perform a genomewide scan on the PERGENE data to elucidate further relevant pharmacogenetic targets in the genome related to the treatment benefit of ACE inhibitors.

When the feasibility of pharmacogenetic profiling of ACE inhibitor therapy is confirmed in other studies, pharmacogenetic analyses of clinical trials will truly offer the prospect of individualizing preventive therapy in patients with cardiovascular disease. Physicians will be able to predict response to treatment (responders and nonresponders) in advance, before starting prescription.

A similar approach could be used for other cardiovascular drugs, such as statins, to optimize patient benefits as strong consistency in treatment benefit has been demonstrated as well.33 Combining these cardiovascular drug trial results could be used to develop a pharmacogenetic profile for cardiovascular drugs in general. We advocate that future large-scale randomized clinical trials integrate pharmacogenetic analysis in their trial design to prospectively test treatment efficacy in a similar way to that usually done with clinical risk factor assessment of trial patients. “Individualized therapy” using pharmacogenetic profiling will avoid unnecessary treatment of nonresponding patients and considerably reduce healthcare costs.

Summary

In the EUROPA trial, 50 patients with stable CAD needed to be treated with perindopril 8 mg/day for a period of 4.2 years to prevent one major cardiovascular event.10 Several attempts have been made to target ACE inhibitor therapy at specific clinical subgroups to give the most treatment benefit. But until now, treatment benefit of ACE inhibitors in stable CAD has been consistent and clinical characteristics cannot be used to target ACE inhibitor therapy. The field of pharmacogenetics could be a new way to test the consistency of the treatment effect of ACE inhibitors. The PERGENE project is unique not only because of its size, randomized design, accurate phenotypic data, and complete coverage of two pathways (RAAS and bradykinin), but also because of the extensive and comprehensive SNP selection procedure involving multiple SNPs in multiple genes of both pathways, integrating information on the haplotype structure of RAAS and bradykinin genes. At present, attempts to target therapy using simple clinical patient characteristics have been unsuccessful at directing ACE inhibition therapy, and it is not yet possible to tell in advance who to treat.19-21

New and improved approaches that integrate more patientspecific characteristics are needed to better target ACE inhibitor therapy. We will investigate whether specific genetic polymorphisms in RAAS genes modify the treatment effect of ACE inhibitor therapy. Our aim is to develop a pharmacogenetic profile associated with the benefit of ACE inhibitor therapy in patients with stable CAD. If it is possible to construct a pharmacogenetic profile related to treatment benefit, this could lead to a significant reduction in the number of patients needed to treat. A pharmacogenetic profile related to the benefit of perindopril may enable the selection of those patients ahead of treatment. Likewise, targeting therapy in only those patients that are likely to benefit will considerably increase the cost-effectiveness of treatment. Cardiovascular pharmacogenetic research is still in a stage of development, but it has the potential to enhance individualized medicine and tailored therapy in cardiovascular medicine.

Executive summary
– ACE inhibitors reduce cardiovascular risk in patients with stable CAD
– Assessing the consistency of treatment benefit is crucial for efficacy and cost-effective prescription of ACE inhibitors
– Treatment benefit of ACE inhibitors is not modified by clinical characteristics. Thus directing ACE inhibitor therapy does not appear feasible using clinical characteristics
– The PERGENE study is a pharmacogenetic analysis of the treatment benefit of ACE inhibitors in a large randomized placebo-controlled clinical trial of patients with stable CAD
– Discovery of a pharmacogenetic profile will optimize patient treatment benefits and reduce unnecessary treatment of patients and health-care costs.

The PERGENE study is supported by a grant from the Netherlands Heart Foundation (NHS2005B219). Dr Brugts is supported by a grant from the Netherlands Heart Foundation (NHS2005B219) and a grant from the Netherlands Organization for Health Research and Development (ZonMW).

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Keywords: pharmacogenetics; ACE inhibitors; perindopril; gene; haplotype; polymorphism; coronary artery disease; secondary prevention