Research Article
Austin J Cardiovasc Dis Atherosclerosis. 2015;2(1): 1009.
Apolipoprotein E Polymorphism is not Associated with Statin Induced Myalgia/Myopathy
Hubacek JA¹*, Schwarzova L², Zlatohlavek L², Adamkova V³, Ceska R² and Vrablik M²
¹Center for Experimental Medicine, Institute for Clinical and Experimental Medicine, Czech Republic
²3rd Department of Medicine, 1st Faculty of Medicine of Charles University and General University Hospital in Prague, Czech Republic
³Department of Preventive Cardiology, Institute for Clinical and Experimental Medicine, Czech Republic
*Corresponding author: Jaroslav A. Hubacek, Center for Experimental Medicine, Institute for Clinical and Experimental Medicine, IKEM-DEM-LMG, Videnska 1958/9 140 21, Prague 4, Czech Republic,
Received: November 25, 2014; Accepted: February 17, 2015; Published: February 19, 2015
Abstract
Statin treatment is the most commonly used way to lower plasma cholesterol levels and prevent cardiovascular disease. The variability of the lipid response seems to be dependent on APOE variant and carriers of APOE4 allele are less responsive to statins than others. As the potential mechanism of such effect is unclear, we hypothesise, that APOE4 carriers could be more prone to the statin side effect, leading to the lower compliance, causing the false effect of lower efficacy. We have successfully genotyped 621 adult patients treated with statins (166 with myalgia/myopathy) and 667 population controls. As expected, carriers of the APOE4E3 and APOE4E4 genotypes were more common among the patients (25.0% vs 16.6%, P < 0.0005). However, the frequencies of the individual APOE genotypes were identical within the groups of patients on statins with and without the myalgia/myopathy (P = 0.99 for codominant model of the analysis). We conclude that it is very unlikely that the lower efficacy of statins in patients with APOE4 allele is a consequence of the higher risk of statin induced side effects in these patients.
Keywords: Apolipoprotein E; Polymorphism; Cholesterol; Treatment; Statin; Myopathy/Myalgia
Introduction
High levels of plasma total- and/or LDL - cholesterol are an independent risk factor for cardiovascular disease [1].
As majority of the patients do not respond sufficiently to the lifestyle interventions (most commonly some dietary restrictions and enhanced physical activity), the pharmacological treatment is the usual way to achieve recommended target lipid levels, and statins (inhibitors of the 3-hydroxymethyl glutaryl coenzyme A reductase, the key enzyme in the biosynthesis of the cholesterol) are the drugs of first choice in this case [2]. High interindividual response variability among individuals treated with the equipotent doses was observed [3], and it has been estimated that up to 70% of the effect of statins is attributable to genetic variation [4] with many other important confounders - e.g. sex, age, physical activity, alcohol intake, or type of diet consumed.
The effect of the common variants within the apolipoprotein E (APOE, gene ID 348, OMIM acc. no. 107741) on plasma cholesterol are consistent over all so far analysed populations. Carriers of the APOE4 (Cys112 → Arg, rs429358) allele have higher total cholesterol levels, while APOE2 (Arg158 → Cys, rs7412) allele carriers have lower cholesterol in comparison to the most common APOE3E3 homozygotes [5].
Because of these facts, many pharmacogenetic studies focused on the potential impact of the common APOE variants on statin treatment efficacy.
Despite some inconsistency among the studies (almost half of the studies found no effect), APOE4 carriers seems to have poorer response to statin treatment and individuals with the APOE2 allele appear to profit more from the treatment (rewieved by [6]).
These differences could have (so far unknown) physiological background or, more simply, could reflect the association between the APOE genotype and statin induced undesirable effects, going hand in hand with lower compliance to statin therapy. A large meta-analysis of almost 80 000 patients, provide the results that statin treatment is associated with low, however, not negligible risk of undesirable side effects [7]. The most frequent side effect in statin treated patients is myopathy [8] that occurs in different forms (myalgia, myositis, rhabdomyolysis) in 3 - 10% of patients. A significant contribution of genetic background to individual susceptibility for undesirable effects of statins is certain [4].
There has been so far also just one published study focusing on the possible effect of the APOE on the statin compliance [9]. Among almost 800 patients treated with statins, individuals carrying the APOE4 allele were under more than double risk to discontinue their drug use. One reason for this fact could be the lower effectiveness associated with this allele. Another possibility could be a different susceptibility to side effects in APOE4 carriers. However, to our knowledge there is no direct study on the topic of adverse effects of statins and APOE polymorphism published.
We have analysed APOE variant in a group of the patients treated with statins, with part of them developing the myopathies.
Materials and Methods
Patients with primary dyslipidemia indicated to statin treatment were retrospectively selected from databases of Lipid Clinics of the 3rd Department of Internal Medicine of the 1st Faculty of Medicine, Charles University and the Institute for Clinical and Experimental Medicine, Prague, the Czech Republic [10]. Six hundred thirty eight adult patients were included, average age 58.5 ± 12.6 years (261 males) (for more details, see Table 1). Patients taking simvastatin (45.6%), atorvastatin (42.0%) and lovastatin (12.4%) in doses of 10 (~90% of individuals) or 20 mg/day were enrolled in the study. We did not include subjects on combination lipid-lowering therapy (e.g. statinfibrate, statin-ezetimibe …). The individuals fulfilling the clinical and laboratory criteria of familial hypercholesterolemia were not included in the study. Criteria for the definition of statin induced adverse effect (myalgia/myopathy) were used as described in details elsewhere [8] and were based on self reported muscle problems resolving with the interruption of therapy, elevation of CK over 5x upper normal limit and family history of myalgia/myopathy.
Patients
Population control
With myalgia/myopathy
Without myalgia/myopathy
N
166
455
667
% of males
38.6
43.3
40.3
Age (years)
62.9 ± 13.1
60.5 ± 13.8
62.0 ± 3.5
Total cholesterol (mmol/l)
7.1 ± 1.6
7.4 ± 1.8
5.8 ± 1.0
Diabetes (%)
22.3
19.9
17.7
Smoking (%)
29.6
28.3
16.2
Obesity (%)
31.6
32.7
45.1
No significant differences have been detected between the patients with and without myalgia/myopathy.
Table 1: Basic characteristic of analyzed individuals.
As a population control group, a subset of the Czech post- MONICA study (675 individuals, upper age quartile of the entire population) was used [11] (Table 1).
All participants of the study were of Caucasian ethnicity from the Central European Czech population. Written informed consent was obtained from all the study participants and the local ethics committee approved the design of the study according to the Declaration of Helsinki of 1975.
Three millilitres of whole blood collected into EDTA tubes for DNA isolation were stored at -20°C. The DNA was isolated using the standard salting out method [12]. APOE gene fragment with two polymorphisms was genotyped using PCR – RFLP method as described in more details elsewhere [13].
The Hardy-Weinberg test was applied to confirm the independent segregation of the alleles. Genotype frequencies between the examined groups were compared individually (using www tool https://www.physics.csbsju.edu/cgi-bin/stats/contingency_form. sh?nrow=2&ncolumn=3) for each polymorphism in 6x2 table and each genotype with the rest of the group in 2x2 table. Distinct combinations pooling together i) carriers of the APOE2/E2 and APOE2/E3 genotypes ii) APOE4/E3 and APOE4/E4 genotypes and iii) APOE3/E3 homozygotes (in this case APOE2/E4 heterozygotes were omitted and 3x2 table was used for the analysis) have been used.
As there have been no significant differences in age, gender, and prevalences of obesity, smoking and diabetes between the patients with and without statin induced myalgia/myopathy, no adjustments have been performed.
Results and Discussion
Hardy-Weinberg test confirmed independent segregation of individual alleles in both groups. The call rate for the APOE polymorphism was very high in both groups – 97.3% for the patients and 98.8% for the controls resulting with 166 patients with myopathy/ myalgia, 455 patients without myopathy/myalgia and finally with 667 controls.
In the control population, the APOE allelic (E2 = 7.3%, E3 = 82.9% and E4 = 9.7%) and genotype frequencies were fully comparable with the so far published frequencies obtained in other Caucasian populations [14]. No gender differences in genotype frequencies were observed either in the patients or in controls (data not shown in details).
As expected the carriers of the APOE4 allele were significantly more prevalent in the patients (as patients on statins have higher plasma lipids) than in the controls (25.0% vs. 16.6%, P < 0.0005) (Table 2). Within the patients treated with statins, the frequencies of the individual genotypes were almost identical (P = 0.99 for codominant model of the analysis) in a subgroup with and without myopathy/myalgia (Table 2). Also other models of the analyses (dominant or recessive) reveal no significant differences (not shown in details). This result almost excludes the possibility, that variants within the apolipoprotein E gene could be significant predictors of statin induced myalgia/myopathy.
APOE
Patients with myopathy/myalgia
Patients without myopathy/myalgia
Controls
genotype
N
%
N
%
N
%
Total
166
455
667
E2/E2
1
0.6
7
1.5
3
0.5
E3/E2
9
5.4
20
4.4
81
12.1
E3/E3
111
66.9
306
67.3
461
69.1
E4/E3
38
22.9
102
22.4
103
15.4
E4/E4
4
2.4
11
2.4
8
1.2
E4/E2
3
1.8
9
2.0
11
1.7
Both groups of patients significantly differ from the controls (P = 0.005 and P = 0.0005). Distribution of the APOE genotypes was almost identical within the patients treated with statins with and without the myalgia/myopathy (P = 0.99, if E2/E2 + E3/E2 vs. E3E3 vs. E4/E3 + E4/E4 were compared).
Table 2: Distribution of the apolipoprotein E genotypes in analyzed groups.
Thus our theory that APOE4 carriers have lower compliance, due to the higher frequency of undesirable side effects than others, seems not to be valid. A large number of gene polymorphisms has been implicated as potentially causal in the development of adverse effects of statins [8,15]. However, most studies assessing impact of genetic background on statin induced adverse effects suffer from the lack of sufficient power (some of them reviewed by [16]). Major issues concern the insufficient number of patients included (as a consequence of the relative low frequency of this condition) and substantial heterogeneity of concomitant treatment as well as study population selection. The interest of medical community in the understanding of the genetic determination of statin adverse effect is obvious. Compared to common biochemical assays analysis of the genetic information yields steady results at relatively low cost and a very robust reproducibility.
In our pilot study, we have detected identical distribution of the common six APOE genotypes between the patients treated by statins with and without myalgia/myopathy. Despite the relative low number of included individuals, there is little reason to consider the use of APOE genotyping as a predictor of statin induced myalgia/myopathy.
6. Acknowledgement
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