Excessive activity of free oxygen radicals has been associated with atherosclerosis.1 Although the use of antioxidants is considered a potential therapy for coronary artery disease (CAD),2 the existing human data provide insufficient evidence for recommending antioxidant supplementation for the prevention or treatment of CAD.3 Nevertheless, it is of interest to examine whether different beta-adrenergic blocking agents exert different antioxidative effects. The Carvedilol Acute Myocardial Infarction Study (CAMIS) compared the efficacies of carvedilol (a nonselective beta-adrenergic receptor blocker with vasodilating properties that has shown antioxidative activity in experimental models and in humans)4,5 and atenolol (a beta-1-selective beta-adrenergic receptor blocker) in patients with an acute myocardial infarction (AMI), with a follow-up time of 12 months.6
The biochemistry of oxidative stress is particularly relevant to lipid peroxidation.7 There are data supporting that oxidatively modified low-density lipoprotein cholesterol (ox-LDL) is a more potent proatherosclerotic mediator than the native unmodified LDL and that an endothelium exposed to ox-LDL develops early signs of injury.8,9 It has been shown that ox-LDL is associated with acute coronary syndromes,3,10-12 and in vitro studies have indicated that vitamin E can inhibit the oxidation of LDL.3 Furthermore, it has been demonstrated that levels of malondialdehyde, measured as thiobarbituric acid reactive substances (TBARS), are elevated in the presence of cardiovascular risk factors such as cigarette smoking, hypertension, hyperlipidemia, and diabetes.13 An increase in TBARS and a decrease in serum levels of vitamin E have been shown in patients with an AMI.14
This randomized prospective study compared the antioxidative properties of carvedilol and atenolol-based on measurements of the circulating levels of ox-LDL, vitamin E, and TBARS-during long-term treatment in post-AMI patients.
MATERIALS AND METHODS
Study Population and Design
A total of 232 patients from the CAMIS were included in this study, of which 220 patients were still receiving the study treatment after 12 months. Blood samples were available at baseline and at 12 months in 204 and 188 randomly selected patients for ox-LDL and TBARS measurements, respectively (Table 1). Vitamin E was analyzed in a subset of 85 patients randomly selected from the total population. The study design has been described in detail previously.6,15 The CAMIS was a single-center, open, end-point-blinded, randomized-controlled comparison of the effects of carvedilol and atenolol in patients with an AMI. Informed consent was obtained from all patients, and the study was approved by the National Committees for Research Ethics in Norway. Patients between 18 and 80 years of age with chest pain consistent with an AMI were included in the study if admitted to the hospital within 24 hours after the onset of symptoms and with the diagnosis confirmed by a significant increase in cardiac enzymes with or without ECG changes. Patients already treated with beta-adrenergic receptor blockers during the previous 3 months; with bradycardia, hypotension, or atrioventricular block of grade 2 or 3; or with severe chronic obstructive pulmonary disease were excluded.
In the main study the patients were randomized to early oral treatment with either carvedilol or atenolol.6 The daily maintenance dose was 36.2 ± 15.1 mg (mean ± SD) in the carvedilol group and 72.1 ± 30.6 mg in the atenolol group. As soon as possible after verification of the diagnosis, and after drawing of blood samples, the patients started treatment with either atenolol (12.5 mg bid) or carvedilol (6.25 mg bid). If tolerated, the dose was continued on a twice-daily basis for each drug and uptitrated over a 6week period. The treatment goal was 50 mg bid for atenolol and 25 mg bid for carvedilol. Of the patients, 53% in the atenolol group and 53% of the patients in the carvedilol group reached the target dose of treatment. The median follow up was 595 days, with a range of 1-1499 days.
In the antioxidative trial, 71% of the patients received early reperfusion therapy (percutaneous coronary intervention and/or thrombolysis) in both study groups (Table 2), and at discharge from hospital 100% of the patients were receiving aspirin and/or warfarin, 98% were receiving statins, 30% were receiving an angiotensin-converting enzyme (ACE) inhibitor or angiotensin II receptor blocker, and 14% were receiving diuretics. During the follow-up period and at the end of the study there were only minor changes in the use of aspirin, statins, and ACE inhibitor or angiotensin II receptor blockers (Table 3), with no difference between the 2 beta-adrenergic receptor antagonist groups. All patients included in the study were receiving beta-adrenergic receptor antagonists at the end of the follow-up period.
None of the patients were allowed to receive nonaspirin, nonsteroidal antiinflammatory drugs, or vitamin E during the study.
Peripheral blood samples were taken at the commencement of the study before the first dose of study drugs was given (within 24 hours from the onset of the AMI) and after 12 months of treatment (in a fasting state at 0800-1000 AM) at 12 hours after the last dose of study drug was given. Blood samples for ox-LDL determination were immediately immersed in ice-cold water and centrifuged within 10 minutes at 2500 × g (gravity) and +4°C for 20 minutes; then the EDTA (ethylenediamine tetraacetic acid) plasma was pipetted off. Serum was prepared within 1 hour for the determination of vitamin E and TBARS. Serum and plasma samples were stored at -70°C until batch analysis was performed.
Ox-LDL was measured with an ELISA (enzyme-linked immunosorbent assay) method (Mercodia, Uppsala, Sweden) based on a direct sandwich technique in which 2 monoclonal antibodies are directed against separate antigenic determinants on the oxidized apolipoprotein B molecule. TBARS were determined with a spectrophotometric method according to Kosugi et al.16 Vitamin E was analyzed using a high-performance liquid chromatography (HPLC) system (Shimadzu/Waters) as described by Brude et al with minor modifications.17 The interassay coefficients of variation were 9% for ox-LDL, 3% for vitamin E, and 8% for TBARS. The global left-ventricular ejection fraction (LVEF) at baseline was determined within 5 days by gated blood-pool scintigraphy.18,19 All laboratory staff who performed the biochemical analyses and measurements of LVEF were blinded to the treatment modalities.
The Mann-Whitney test or Wilcoxon test was used to compare data with skewed distributions, and Student's t test was used for normally distributed data.20 Changes in the markers of oxidative stress over time were assessed by a covariance model with repeated-measures (ANCOVA)21 adjusted for potential confounders. Results are expressed as mean ± standard deviation (SD) values, with a 2-tailed probability value of P < 0.05 being considered significant.
The data for individuals with blood samples available for ox-LDL are listed in Tables 1-4; those for vitamin E and TBARS did not differ significantly. The baseline characteristics, acute treatment, and medication at discharge from hospital and at the end of the study period (Tables 1, 2, and 3) did not differ significantly between patients receiving carvedilol and atenolol, except that the number of females was significantly higher in those receiving atenolol. No differences were observed in heart rate and blood pressure between the carvedilol and atenolol groups (Tables 1 and 4), which suggests that the 2 drugs had been given at equipotent doses.
Ox-LDL levels decreased significantly in both the carvedilol (P = 0.0001) and atenolol (P = 0.044) groups, with there being a significant between-group difference in the changes (P = 0.036) (Figure 1). The vitamin E levels did not change in the carvedilol group, whereas a marginal reduction was observed in the atenolol group (P = 0.056), with a significant between-group difference (P = 0.008) (Figure 2). The TBARS levels were reduced in both groups, although this was only significant in the atenolol group (P = 0.020). However, there was no significant difference in changes between the groups (P = 0.454) (Figure 3).
This is the first long-term randomized parallel-group study comparing markers of oxidative stress of 2 beta-adrenergic receptor blockers in patients after an AMI. The results indicate that carvedilol exerts a stronger antioxidant effect than atenolol, as assessed by the ox-LDL and vitamin E levels. Our results are in accordance with previous studies in humans with essential hypertension, which found that carvedilol exerted a selective antioxidant effect.22-24 Nitric oxide (NO) is an endothelium-derived relaxing factor.25,26 A short-term trial involving patients with hypertension27 has compared a more beta-1-selective-adrenergic receptor blocker that exerts vasodilating effects caused by endothelium-dependent relaxation, nebivolol, with the effects of atenolol, and both were found to reduce blood pressure. In addition, oxidative stress markers such as ox-LDL were decreased more significantly by nebivolol than by atenolol. Improvement in NO availability, which reverses endothelial dysfunction in essential hypertension in patients treated with nebivolol and contributes to vasodilation,28 is not only the result of the previously known increased effects on endothelial NO synthase (eNOS activity) and hence NO,29 but also due to the antioxidant properties of nebivolol.27
The absence of a difference in the heart rate and blood pressure between the 2 drugs in our study-suggesting equipotent doses-has been observed previously.6,15 Many biomarkers have been proposed for evaluating oxidative stress.8 Although none of them have been shown to be superior, lipid peroxidation has received considerable attention, including LDL oxidation. Elevated levels of ox-LDL have been associated with the development of CAD,10,30,31 and ox-LDL has been found to be elevated in individuals who subsequently developed AMI.32,33 Furthermore, compared with age-matched controls, the levels of ox-LDL have been found to be higher in patients without clinical evidence of CAD but with angiographically verified CAD.34 The plasma levels of ox-LDL are also reportedly higher in patients with acute coronary syndromes than in patients with stable angina.10
In patients who have received a heart transplant, the plasma levels of ox-LDL are correlated with both the severity of the coronary artery stenoses and the extent of the CAD.35 Oxidative modification of LDL, an early event in the formation of atherosclerotic plaques,36,37 is inhibited by vitamin E in vitro.38 An inverse association between plasma vitamin E and the risk of developing angina pectoris has also been observed in case-control studies.39 However, randomized studies have not found any effect of vitamin E supplements in the primary prevention of coronary events, and their use in secondary prevention is controversial.3
In the present study, vitamin E levels decreased in the atenolol group but increased slightly in the carvedilol group. This difference might be of clinical relevance because vitamin E might modify and inhibit the formation of atherosclerotic plaques.36-38 The decrease in the atenolol group might also be attributable to consumption of serum vitamin E during ongoing peroxidation.
Increased levels of TBARS have been reported in both patients with stable CAD and those with congestive heart failure.13,40 Despite the suggestion of a unique antioxidative effect of carvedilol compared with other beta-adrenergic receptor blockers,4 in our study TBARS declined by almost the same amount with treatment modality and time in both groups; the reason for this is unclear. The patients in our 2 study groups were treated equally with statins. Various studies have shown that statins affect lipid peroxidation, which could at least partly explain why no significant difference in TBARS was observed between the groups.41 However, our results are in accordance with a study that found no difference in TBARS levels in patients with congestive heart failure who were treated with the 2 beta-adrenergic receptor blockers carvedilol and metoprolol.40 The spectrophotometric method used in our study is a nonspecific and crude measure of peroxidation; HPLC is a more specific method measuring TBARS, but it is impractical for large studies.8
Studies have demonstrated marked increases in sympathetic activity and oxidative stress during AMI.11,42-46 Elevations in plasma catecholamines and sympathetic stimulation have been found after an AMI,42-46 with the latter being linked to the production of free oxygen radicals and to endothelial damage, dysfunction, and the progression of atherosclerosis.47-49 We have previously reported that the inhibition of sympathetic activity was greater for carvedilol than for atenolol in the present population,15 which could also partly explain the more beneficial antioxidative effect of carvedilol.
The present results indicate that carvedilol has a more pronounced antioxidative effect than atenolol in post-AMI patients, when evaluated based on the levels of ox-LDL and vitamin E. Because lipid and protein peroxidation are important in the formation of atherosclerotic plaques, the observed effects of carvedilol might be clinically useful in the treatment of patients with CAD.
We gratefully acknowledge the inestimable technical assistance of the staff at the Department of Nuclear Medicine and the Center of Clinical Research, Ullevaal University Hospital, University of Oslo, and of Ida G. Bay, Department of General Practice and Community Medicine, University of Oslo.
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