Patients with histories of myocardial infarction display shortened leukocyte telomere length (LTL), but conflicting findings have been reported on the relation between LTL and subclinical coronary artery atherosclerosis, as expressed by coronary artery calcium (CAC). The aim of this study was to examine the relation between LTL, measured by Southern blots, and CAC in 3,169 participants in the National Heart, Lung, and Blood Institute Family Heart Study. Participants consisted of 2,556 whites, 613 blacks, 1,790 women, and 1,379 men. The odds of having CAC ≥100 for the shortest LTL tertile versus the longest LTL tertile were 1.95 (95% confidence interval [CI] 1.28 to 3.16) in white men and 1.76 (95% CI 1.18 to 2.45) in white women, after adjusting for multiple covariates of CAC. The corresponding odds ratios for blacks were 1.53 (95% CI 0.67 to 3.50) and 0.87 (95% CI 0.37 to 2.00). Significance levels of tests for trend across LTL tertiles were p = 0.002 in white men, p = 0.006 in white women, p = 0.32 in black men, and p = 0.74 in black women. The associations, or lack of associations, were independent of C-reactive protein levels and other risk factors for CAC. As previously shown in other studies, whites displayed shorter LTLs than blacks (p <0.0001). In conclusion, the higher the coronary artery atherosclerotic burden in whites, the shorter the LTL. This LTL-atherosclerosis connection is not found in blacks. The mechanisms for the racial difference in LTL, CAC, and their interrelations do not seem to be related to inflammation and merit further research.
Cardiovascular disease, principally in the form of atherosclerosis, and leukocyte telomere length (LTL) are associated with aging and ostensibly with each other. A recent meta-analysis, although confirming that patients who have had myocardial infarctions have shorter LTLs than their peers, failed to show a significant association of LTL with coronary artery disease, the root cause of most cases of myocardial infarction. Coronary artery calcium (CAC) is a highly sensitive and specific index of coronary artery disease risk, because arterial calcium is pathognomonic of atherosclerosis and also a sensitive indicator of atherosclerotic plaque burden in the coronary arteries. A body of research indicates that independent of traditional risk factors, CAC predicts myocardial infarction. Even in the presence of multiple cardiac risk factors, subjects with no evidence of CAC have low near-term risk for myocardial infarction. Here we present the relation of LTL with CAC on the basis of a cohort comprising 3,169 participants in the National Heart, Lung and Blood Institute Family Heart Study. This work has also examined whether gender, ethnicity (black or white), and high-sensitivity serum C-reactive protein (CRP) affect the association of LTL with CAC.
Methods
The NHLBI Family Heart Study is a multicenter investigation of the genetic and epidemiologic basis of cardiovascular disease. From January 2002 to January 2004, 3,359 subjects were examined (2,737 whites, 622 blacks). These subjects had either participated in previous clinic visits from February 1994 to March 1996 or were newly recruited blacks from the Hypertension Genetic Epidemiology Network field center in Birmingham, Alabama. The study protocol was approved by the institutional review board at each of the participating centers, and each participant gave written informed consent.
Ethylenediamine tetra-acetic acid blood was stored at −70°C until shipment to the Center of Human Development and Aging at the New Jersey Medical School, Rutgers, for LTL measurement. Deoxyribonucleic acid (DNA) was extracted using the Gentra Puregene Blood Kit (Qiagen, Valencia, California), and samples were subjected to DNA integrity tests. LTL was derived from the mean length of the terminal restriction fragments, determined by Southern blot analysis. The interassay coefficient of variation for duplicate samples, which were resolved on different gels on different occasions, was 2.4%.
CAC measurements were obtained from 5 field centers using 4-slice multidetector computed tomographic systems without contrast (GE Health Systems LightSpeed Plus and LightSpeed Ultra, Siemens Volume Zoom, or Philips MX 8000). The protocol and scoring (Agatston score) at a central reading laboratory have been previously described and were consistent across centers.
Measurements of glucose and lipid levels were performed on fasting blood samples. Thirty-six subjects who were fasting for <6 hours were excluded from all analyses. High-sensitivity serum CRP was measured at the Laboratory for Clinical Biochemistry Research, University of Vermont, using an enzyme-linked immunosorbent assay method calibrated with World Health Organization reference material. The New Jersey and Vermont laboratories were blinded to the identities of the subjects.
Pack-years of smoking were obtained by a questionnaire. An automated blood pressure device (Dinamap Monitor Pro 100) was used to record 3 measurements of blood pressure, 1 minute apart. Hypertension was defined as currently taking antihypertensive medications or an untreated blood pressure of ≥140/90 mm Hg. Medication use for hypertension or dyslipidemia was obtained from each subject and coded as current or not for this analysis.
Subject characteristics were compared across gender and race categories using generalized estimating equations and an exchangeable correlation matrix to model the relatedness of the subjects (PROC GENMOD; SAS Institute Inc., Cary, North Carolina). To examine the mean LTL by 4 different CAC categories (0, 1 to 99, 100 to 399, and ≥400 Agatston units), we first adjusted LTL for age and analyzed the means of the residuals after the overall mean was added back to each residual. A test for a linear trend across the categories was performed using contrasts in this same model. Tertiles of LTL were analyzed for the primary association tests so that a linear relation between LTL and CAC did not need to be assumed.
To predict the risk for developing significant coronary atherosclerotic calcium, CAC was modeled as a dichotomous dependent variable (CAC ≥100 vs CAC <100) in a logistic general linear model that incorporated the effects of LTL nested within gender and race categories as the independent variable, the relatedness of the sample, and multiple covariates that have been shown to be related to the development of CAC. Two sets of covariates were used for additional statistical adjustment. First, adjustment was performed using age and body mass index (BMI) only as covariates. The second set of covariates included age, BMI, pack-years of smoking, glucose, low-density lipoprotein cholesterol, high-density lipoprotein (HDL) cholesterol, triglycerides, mean arterial blood pressure, blood pressure medication status, and CRP. Gender-combined models included an adjustment for gender.
Results
A total of 3,169 of 3,359 subjects had LTL measurements. The 190 subjects without LTL measurements were those who did not provide blood samples to obtain DNA, those who had too little DNA for LTL measurement, and whose samples failed the DNA integrity tests. Table 1 lists the characteristics of the subjects. Women were slightly older and had lower diastolic blood pressure, higher CRP and HDL cholesterol, but lower fasting glucose and triglycerides compared with men. Blacks were younger and displayed higher BMIs, systolic and diastolic blood pressures, higher CRP, fasting glucose and HDL cholesterol, and lower triglycerides than whites. Fewer women than men were smokers. Compared with whites, more blacks were current smokers and taking antihypertensive medications, and fewer were taking lipid-lowering drugs.
| Variable | Black | White | p-value ∗ | |||
|---|---|---|---|---|---|---|
| Men (N=215) | Women (N=398) | Men (N=1164) | Women (N=1392) | Gender Effect ∗ | Race Effect ∗ | |
| Age (year) | 52±0.7 | 54±0.6 | 57±0.4 | 58±0.4 | 0.01 | <0.0001 |
| Body mass index (kg/m 2 ) | 30.4±0.4 | 33.8±0.4 | 29.3±0.2 | 28.4±0.2 | 0.47 | <0.0001 |
| Systolic blood pressure (mmHg) | 132±1.4 | 133±1.2 | 122±0.5 | 119±0.6 | <0.0001 | <0.0001 |
| Diastolic blood pressure (mmHg) | 79±0.8 | 74±0.6 | 73±0.3 | 67±0.3 | <0.0001 | <0.0001 |
| Coronary arterial calcium (Agatston) | 342±44 | 166±19 | 521±29 | 125±13 | <0.0001 | 0.09 |
| Leukocyte telomere length (kb) | 6.85±0.04 | 7.11±0.03 | 6.73±0.02 | 6.87±0.02 | <0.0001 | <0.0001 |
| C-reactive protein (mg/l) | 4.6±0.4 | 7.6±0.5 | 2.8±0.1 | 4.1±0.2 | <0.0001 | <0.0001 |
| Glucose (mg/dl) | 116±3.0 | 111±2.2 | 103±0.8 | 97±0.6 | <0.0001 | <0.0001 |
| Low density lipoprotein cholesterol (mg/dl) | 113±2.6 | 116±1.8 | 109±1.0 | 112±1.1 | 0.01 | 0.03 |
| High density lipoprotein (mg/dl) | 47±1.1 | 57+0.7 | 42±0.4 | 54±0.5 | <0.0001 | <0.0001 |
| Triglycerides (mg/dl) | 117±5.7 | 110±3.9 | 152±3.2 | 136±2.4 | <0.0001 | <0.0001 |
| Pack-years of smoking | 15.4±1.4 | 7.0±0.6 | 15.9±0.8 | 7.6±0.5 | <0.0001 | 0.49 |
| Antihypertensive drugs | 56% | 70% | 33% | 30% | 0.37 | <0.0001 |
| Lipid lowering drugs | 20% | 15% | 26% | 21% | <0.0001 | 0.16 |
∗ p-value from two-way ANOVA test for gender and race, after adjusting for age.
Age-adjusted LTL was longer in women than in men (6.98 ± 0.02 vs 6.81 ± 0.02, p <0.0001) and in blacks than in whites (7.01 ± 0.03 vs 6.78 ± 0.02, p <0.0001). Shorter LTL was significantly related to increased CAC category, but only in whites ( Table 2 ). Blacks with either CAC = 0 or CAC ≥400 had longer LTLs than those in the 2 intermediate CAC categories, resulting in more of a quadratic relation between the 2 variables. When age-adjusted LTL was divided into tertiles, shorter LTL predicted increased probability of CAC ≥100 in white men and women after adjustment for age and BMI ( Figure 1 ). Odds ratios for CAC ≥100 for the shorter LTL tertile versus the longer LTL tertile were 2.08 (95% confidence interval [CI] 1.38 to 3.13) for white men and 1.55 (95% CI 1.06 to 2.28) for white women after age and BMI adjustment. After including other covariates that have been related to CAC in the model (mean arterial pressure, low-density lipoprotein cholesterol, HDL cholesterol, triglycerides, pack-years of smoking, and CRP), the previous odds ratios were only slightly reduced and remained significant (1.95 [95% CI 1.28 to 3.16] for white men and 1.76 [95% CI 1.18 to 2.45] for white women). Significance levels of tests for linear trend across the 3 LTL tertiles were p = 0.002 for white men and p = 0.006 for white women. The odds ratios for blacks ( Figure 1 ) were not significant (1.53 [95% CI 0.67 to 3.50] for black men and 0.87 [95% CI 0.37 to 2.00] for black women) in the fully adjusted model. Results of tests for linear trends across the LTL tertiles in blacks were p = 0.32 for men and p = 0.74 for women.
| CAC | Black | White | ||||
|---|---|---|---|---|---|---|
| Men | Women | Both | Men | Women | Both | |
| 0 | 6.98±0.08 (82) | 7.20±0.04 (205) | 7.08±0.04 (287) | 6.78±0.04 (300) | 6.85±0.03 (721) | 6.80±0.02 (1021) |
| 1-99 | 6.92±0.07 (71) | 7.16±0.06 (127) | 7.04±0.05 (198) | 6.78±0.03 (371) | 6.88±0.03 (380) | 6.81±0.02 (751) |
| 100-399 | 6.90±0.10 (29) | 7.15±0.09 (36) | 7.02±0.07 (65) | 6.57±0.04 (154) | 6.77±0.05 (147) | 6.69±0.04 (301) |
| ≥400 | 6.97±0.10 (33) | 7.23±0.10 (30) | 7.10±0.07 (63) | 6.61±0.04 (339) | 6.74±0.06 (144) | 6.70±0.03 (483) |
| p ∗ | 0.91 | 0.80 | 0.90 | 0.0003 | 0.036 | 0.002 |
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
