Apolipoprotein B is a stronger predictor of myocardial infarction than LDL cholesterol, and it is inversely related to physical activity and modifiable with exercise training. As such, apolipoprotein measures may be of particular relevance for subjects with PAD and claudication. We compared plasma apolipoprotein profiles in 29 subjects with peripheral artery disease (PAD) and intermittent claudication and in 39 control subjects. Furthermore, we compared the plasma apolipoprotein profiles of subjects with PAD either treated (
Peripheral artery disease (PAD) is a highly prevalent medical condition, [
We have previously found that cardiovascular risk factors, such as dyslipidemia, are associated with impaired ambulation and vascular function in subjects with PAD and claudication [
The classification of plasma lipoproteins based on apolipoprotein composition instead of size and density provides a new way of characterizing plasma lipoproteins as these subclasses differ not only in their apolipoprotein composition but also in their metabolic properties [
In subjects with severe PAD requiring revascularization, women with both localized aortic stenosis and diffuse segmental stenosis have impaired apolipoprotein profiles compared to controls [
Statin therapy improves claudication measures [
The procedures used in this study were approved by the Institutional Review Board at the University of Oklahoma Health Sciences Center and by the Research and Development Committee at the Oklahoma City VA Medical Center. Written informed consent was obtained from each patient prior to investigation.
Subjects participated in this study at the General Clinical Research Center, at the University of Oklahoma Health Sciences Center. Subjects with PAD and claudication were recruited by referrals from vascular and primary care clinics at the University of Oklahoma Health Sciences Center and the Oklahoma City VA Medical Center. Control subjects were recruited by newspaper advertisements for the assessment of cardiovascular risk factors in individuals without a history of cardiovascular diseases.
Subjects with claudication secondary to vascular insufficiency were included in this study if they met the following criteria: (a) a history of ambulatory leg pain [
Control subjects were included in this study if they met the following criteria: (a) no history of ambulatory leg pain [
Subjects arrived in the morning fasted but were permitted to take their usual morning medication regimen. Blood samples were drawn into chilled EDTA (1 mg/dL of blood) containing tubes after an overnight fast.
Blood was analyzed for fasting glucose concentrations as part of the automated chemistry battery (complete metabolic panel). Blood was also analyzed for fasting lipids, apoB, apolipoprotein C-III (apoC-III), and apolipoprotein subparticles consisting of Lp-B-II, Lp-A-II:B:C:D:E, Lp-B:E + Lp-B:C:E, Lp-B, Lp-B:C, Apo AI, Lp-A-I, and Lp-A-I:A-II. Total cholesterol, triglycerides, and high-density lipoprotein cholesterol (HDL-C) were measured by standardized enzymatic procedure [
Blood was frozen at minus 70°C for subsequent analysis of apolipoprotein levels. ApoC-III was measured in the total plasma sample and in the heparin-manganese precipitate (HP), following reconstitution of the original volume. ApoC-III HP represents the apoC-III bound to apoB-containing lipoproteins. ApoC-III in the heparin-manganese supernate (HS) represents apoC-III bound to apoA-containing lipoproteins. The values for apoC-III HS were derived by subtracting apoC-III HP from total plasma apoC-III.
Density-defined lipoprotein classes, including total cholesterol, triglycerides, and HDL-C, were measured as previously described [
After the blood samples were drawn, subjects were seen by a study physician. Demographic information, height, weight, cardiovascular risk factors, comorbid conditions, claudication history, ABI, and a list of current medications were obtained from a medical history and physical examination.
Within each of the three groups, controls, PAD subjects treated with statin, and PAD subjects not treated with statin, measurement variables were summarized as means and standard deviations. Dichotomous variables were summarized as percent with attribute present. As preliminary analysis, the mean ages of the three groups were compared using a one-way ANOVA and sex distributions compared using Chi-Square test in Tables
The clinical characteristics of the PAD groups and the control group are shown in Table
Clinical characteristics of subjects with peripheral artery disease (PAD) and controls. Values are means (standard deviation) or percentage of subjects in each category.
Variables | Control group ( |
PAD no statin group ( |
PAD statin group ( |
|
---|---|---|---|---|
Age (years) | 55 (13) | 66 (13) | 63 (11) | 0.003 |
Sex (% men) | 54 | 67 | 53 | 0.695 |
Diabetes (% yes) | — | 0 | 47 | 0.005 |
Hypertension (% yes) | — | 92 | 69 | 0.144 |
Current smoking (% yes) | — | 67 | 41 | 0.176 |
Coronary artery disease (% yes) | — | 33 | 35 | 0.913 |
Lipid measures of subjects with peripheral artery disease (PAD) and controls. Values are means (standard deviation).
Variables | Control group ( |
PAD no statin group ( |
PAD statin group ( |
ANCOVA |
ΔAdjusted mean = control group − PAD groups | ΔAdjusted mean = PAD no statin group − PAD statin group |
---|---|---|---|---|---|---|
Triglycerides (mg/dL) | 87.5 (41.9) | 154.1 (116.9) | 133.9 (92.3) | 0.011 | −60.6** | 21.6 |
Total cholesterol (mg/dL) | 181.5 (53.2) | 177.8 (31.3) | 157.1 (32.3) | 0.062 | 23.4* | 17.4 |
HDL-C (mg/dL) | 52.4 (15.2) | 44.3 (13.6) | 46.8 (13.7) | 0.016 | 10.7* | −3.9 |
LDL-C (mg/dL) | 117.5 (38.6) | 108.3 (28.0) | 87.2 (26.6) | 0.011 | 23.3** | 20.2 |
LDL-C/HDL-C | 2.35 (0.83) | 2.65 (1.22) | 1.92 (0.64) | 0.078 | −0.1 | 0.77* |
Non-HDL-C (mg/dL) | 129.1 (47.8) | 133.5 (32.9) | 110.3 (27.9) | 0.158 | 12.6 | 21.3 |
Total cholesterol/HCL-C ratio | 3.62 (1.10) | 4.36 (1.60) | 3.56 (1.04) | 0.076 | −0.5 | 0.86 |
Triglyceride/HDL-C ratio | 1.93 (1.48) | 4.19 (3.78) | 3.50 (3.35) | 0.005 | −2.3*** | 0.82 |
HDL-C: high-density lipoprotein cholesterol; LDL-C: low-density lipoprotein cholesterol.
Apolipoprotein measures of subjects with peripheral artery disease (PAD) and controls. Values are means (standard deviation).
Variables | Control group ( |
PAD no statin group ( |
PAD statin group ( |
ANCOVA |
ΔAdjusted mean = control group − PAD groups | ΔAdjusted mean = PAD no statin group − PAD statin group |
---|---|---|---|---|---|---|
ApoB (mg/dL) | 90.9 (12.3) | 93.8 (16.1) | 82.1 (19.2) | 0.085 | 1.7 | 12.0* |
ApoC-III (mg/dL) | 10.1 (3.0) | 10.1 (2.1) | 10.0 (3.4) | 0.890 | 0.4 | 0.0 |
ApoC-III HS (mg/dL) | 6.6 (2.7) | 6.9 (1.3) | 6.5 (2.0) | 0.507 | 0.6 | 0.2 |
ApoC-III HP (mg/dL) | 3.4 (1.3) | 3.1 (0.9) | 3.5 (3.0) | 0.823 | −0.2 | −0.3 |
ApoC-III ratio | 2.26 (1.32) | 2.37 (0.63) | 2.64 (1.46) | 0.552 | 0.19 | −0.42 |
Lp-B-II (mg/dL) | 90.4 (13.2) | 83.6 (17.9) | 81.5 (18.9) | 0.213 | 6.9 | 2.4 |
Lp-A-II:B:C:D:E (mg/dL) | 12.1 (5.8) | 23.0 (33.4) | 10.0 (4.7) | 0.079047 | −3.0 | 12.5* |
Lp-B:E + Lp-B:C:E (mg/dL) | 12.4 (4.5) | 22.6 (26.4) | 12.7 (5.6) | 0.066 | −4.2 | 9.5* |
Lp-B (mg/dL) | 59.8 (7.2) | 50.6 (20.0) | 54.8 (12.1) | 0.127 | 6.1* | −3.8 |
Lp-B:C (mg/dL) | 9.5 (4.0) | 20.0 (21.1) | 10.4 (4.8) | 0.013 | −5.1* | 9.4* |
Apo A1 (mg/dL) | 132.5 (16.5) | 134.8 (20.2) | 124.7 (18.9) | 0.156 | 5.4 | 9.2 |
Lp-A-I (mg/dL) | 34.8 (4.4) | 48.2 (37.9) | 32.5 (6.0) | 0.049 | −3.6 | 15.1* |
Lp-A-I:A-II (mg/dL) | 97.7 (12.9) | 87.0 (27.2) | 92.1 (15.5) | 0.134 | 8.8* | −5.3 |
B/A1 ratio | 0.69 (0.14) | 0.62 (0.13) | 0.66 (0.17) | 0.673 | 0.03 | −0.03 |
Lp-B/C-III HP ratio | 20.15 (8.46) | 18.33 (8.88) | 21.36 (9.34) | 0.461 | 1.78 | −3.54 |
Lipid measures of subjects with PAD and controls are displayed in Table
Apolipoprotein measures of subjects with PAD and controls are displayed in Table
To our knowledge, this is the first study to compare apolipoprotein subparticles in subjects with PAD and claudication compared to control subjects. The PAD groups had a 5 mg/dL higher age-adjusted Lp-B:C value than the control group, a 6 mg/dL lower age-adjusted Lp-B level, and a 9 mg/dL lower age-adjusted Lp-A-I:A-II value.
The higher Lp-B:C particles level in the PAD group supports a previous study with type 2 diabetic patients that showed that levels of Lp-B:C particles were independently associated with macrovascular complications, as defined by the presence of coronary artery disease, PAD or cerebrovascular disease, or more than one of these [
The PAD groups had a 60 mg/dL higher age-adjusted triglyceride level than the control group, a 2.3 higher age-adjusted ratio of triglyceride/HDL-C, an 11 mg/dL lower age-adjusted HDL-C concentration, and a 23 mg/dL lower age-adjusted LDL-C value.
The higher triglyceride level in the PAD group supports a previous observation of a 118% higher triglyceride concentration in subjects with diffuse, stenotic PAD compared to controls [
Surprisingly, the PAD group had lower LDL-C than the controls, possibly because 17 of 29 subjects with PAD were taking statin medications. Since apoB was not different between the PAD and control groups, this suggests that subjects with PAD may have had higher values of intermediate-density lipoprotein cholesterol (IDL-C) and very low-density lipoprotein cholesterol (VLDL-C) because apoB directly measures the total number of atherogenic particles [
To our knowledge, this is the first study to examine the relationship between statin therapy and apolipoprotein subparticles in subjects with PAD and claudication. Subjects with PAD who were taking statin medications had lower values of LDL-C/HDL-C ratio, apoB, Lp-A-II:B:C:D:E, Lp-B:E + Lp-B:C:E, Lp-B:C, and Lp-A-I than subjects who were not taking statin medications. These findings agree with the observation that subjects with PAD who take statin medications have lower LDL-C [
The effects of statins among apolipoproteins subparticles are not uniform and depend on both the type of pharmacological agent and the type of apolipoprotein subparticle being measured [
Another observation was that Lp-A-I was lower in the PAD statin group. This was not expected because Lp-A-I is in the higher density gradient of apolipoprotein subparticles, and it is a major constituent of HDL-C. A possible explanation may be related to the polydisperse character of lipoprotein families within ApoA-I-containing lipoprotein subclasses, as many overlap with the LDL-C class. It is possible that the LDL-C lowering effect of statins resulted in concomitant reduction in the Lp-A-I subparticle.
We have previously found that subjects with PAD receive suboptimal management for dyslipidemia, hypertension, and diabetes [
There are limitations to this study. Subjects with PAD and controls who participated in this trial were volunteers and therefore may represent those who were more interested in exercise and in their health, who had better access to transportation to our research center, and who had relatively better health than PAD subjects and controls who did not volunteer. The cross-sectional design comparing those with and without PAD does not allow causality to be established, as it is possible that unfavorable apolipoprotein and lipid profiles may either precede or be a consequence of the development of PAD and claudication. The present findings are also limited to PAD subjects with a history of claudication. Thus, the current findings cannot be generalized to subjects with less severe PAD (i.e., asymptomatic PAD) or more severe symptoms (i.e., critical leg ischemia) or to those who are limited in their exercise performance by other significant comorbid conditions. Finally, this study consisted of small group sample sizes, and subjects were not recruited as a consecutive series.
Subjects with PAD have worse lipid profiles and impaired apolipoprotein profiles than controls, characterized by Lp-B:C and Lp-A-I:A-II. Furthermore, subjects with PAD on statin medications have a more favorable risk profile, particularly noted in multiple apolipoprotein subparticles. The efficacy of statin therapy to improve cardiovascular risk appears more evident in the apolipoprotein subparticle profile than in the more traditional lipid profile of subjects with PAD and claudication. The possibility of apolipoprotein subparticles as better therapeutic targets for the management of dyslipidemia is an attractive proposition as it may allow identifying patient populations that are at higher risk of developing adverse cardiovascular events and progression of PAD. Moreover the suggestion that statins may selectively alter levels of apolipoprotein subparticles is an endeavor worth pursuing but will need the rigors of a formal randomized control trial. Until then, these results are worth reporting as observed findings in the first study to compare apolipoprotein subparticles in subjects with PAD and claudication compared to control subjects.
Grant support is provided by the National Institute on Aging (R01-AG-24296), Oklahoma Center for the Advancement of Science and Technology (HR09-035), and General Clinical Research Center (M01-RR-14467).