Susan G. Lakoski

Genetic and Metabolic Determinants of Plasma PCSK9 Levels

CONTEXT PCSK9 is a secreted protein that influences plasma levels of low-density lipoprotein cholesterol (LDL-C) and susceptibility to coronary heart disease. PCSK9 is present in human plasma, but the factors that contribute to differences in plasma concentrations of PCSK9 and how they impact on the levels of lipoproteins have not been well-characterized. OBJECTIVE The aim of the study was to measure PCSK9 levels in a large, ethnically diverse population (n = 3138) utilizing a sensitive and specific sandwich ELISA. DESIGN We conducted an observational study in the Dallas Heart Study, a multiethnic, probability-based sample of Dallas County. RESULTS Plasma levels of PCSK9 varied over approximately 100-fold range (33-2988 ng/ml; median, 487 ng/ml). Levels were significantly higher in women (517 ng/ml) than in men (450 ng/ml), and in postmenopausal women compared to premenopausal women (P < 0.0001), irrespective of estrogen status. Plasma levels of PCSK9 correlated with plasma levels of LDL-C (r = 0.24) but explained less than 8% of the variation in LDL-C levels (r(2) = 0.073). Other factors that correlated with PCSK9 levels included plasma levels of triglycerides, insulin, and glucose. Individuals with loss-of-function mutations in PCSK9 and reduced plasma levels of LDL-C also had significantly lower plasma levels of PCSK9 after adjusting for age, gender, and LDL-C levels (P < 0.0001). CONCLUSION Multiple metabolic and genetic factors contribute to variation in plasma levels of PCSK9 in the general population. Although levels of PCSK9 correlate with plasma levels of LDL-C, they account for only a small proportion of the variation in the levels of this lipoprotein.

Lifetime risks for cardiovascular disease mortality by cardiorespiratory fitness levels measured at ages 45, 55, and 65 years in men. The Cooper Center Longitudinal Study.

OBJECTIVES The purpose of this study was to determine the association between fitness and lifetime risk for cardiovascular disease (CVD). BACKGROUND Higher levels of traditional risk factors are associated with marked differences in lifetime risks for CVD. However, data are sparse regarding the association between fitness and the lifetime risk for CVD. METHODS We followed up 11,049 men who underwent clinical examination at the Cooper Institute in Dallas, Texas, before 1990 until the occurrence of CVD death, non-CVD death, or attainment of age 90 years (281,469 person-years of follow-up, median follow-up 25.3 years, 1,106 CVD deaths). Fitness was measured by the Balke protocol and categorized according to treadmill time into low, moderate, and high fitness, with further stratification by CVD risk factor burden. Lifetime risk for CVD death determined by the National Death Index was estimated for fitness levels measured at ages 45, 55, and 65 years, with non-CVD death as the competing event. RESULTS Differences in fitness levels (low fitness vs. high fitness) were associated with marked differences in the lifetime risks for CVD death at each index age: age 45 years, 13.7% versus 3.4%; age 55 years, 34.2% versus 15.3%; and age 65 years, 35.6% versus 17.1%. These associations were strongest among persons with CVD risk factors. CONCLUSIONS A single measurement of low fitness in mid-life was associated with higher lifetime risk for CVD death, particularly among persons with a high burden of CVD risk factors.

Exercise rehabilitation in patients with cancer

Emerging evidence indicates that patients with cancer have considerable impairments in cardiorespiratory fitness, which is likely to be a result of the direct toxic effects of anticancer therapy as well as the indirect consequences secondary to therapy (for example, deconditioning). This reduced cardiorespiratory fitness is associated with heightened symptoms, functional dependence, and possibly with an increased risk of cardiovascular morbidity and mortality. Current understanding of the complex interaction between the effects of the tumour and cancer-associated therapies on the organ components that govern cardiorespiratory fitness, and the effects of exercise training on these parameters is limited; further research will be critical for further progress of exercise-based rehabilitation in the oncology setting. We assess the current evidence regarding the level, mechanisms, and clinical importance of diminished cardiorespiratory fitness in patients with cancer. The efficacy and adaptations to exercise training to prevent and/or mitigate dysfunction in conjunction with exercise prescription considerations for clinical use are also discussed.

Low-Risk Lifestyle, Coronary Calcium, Cardiovascular Events, and Mortality: Results From MESA

Unhealthy lifestyle habits are a major contributor to coronary artery disease. The purpose of the present study was to investigate the associations of smoking, weight maintenance, physical activity, and diet with coronary calcium, cardiovascular events, and mortality. US participants who were 44-84 years of age (n = 6,229) were followed in the Multi-Ethnic Study of Atherosclerosis from 2000 to 2010. A lifestyle score ranging from 0 to 4 was created using diet, exercise, body mass index, and smoking status. Coronary calcium was measured at baseline and a mean of 3.1 (standard deviation, 1.3) years later to assess calcium progression. Participants who experienced coronary events or died were followed for a median of 7.6 (standard deviation, 1.5) years. Participants with lifestyle scores of 1, 2, 3, and 4 were found to have mean adjusted annual calcium progressions that were 3.5 (95% confidence interval (CI): 0.0, 7.0), 4.2 (95% CI: 0.6, 7.9), 6.8 (95% CI: 2.0, 11.5), and 11.1 (95% CI: 2.2, 20.1) points per year slower, respectively, relative to the reference group (P = 0.003). Unadjusted hazard ratios for death by lifestyle score were as follows: for a score of 1, the hazard ratio was 0.79 (95% CI: 0.61, 1.03); for a score of 2, the hazard ratio was 0.61 (95% CI: 0.46, 0.81); for a score of 3, the hazard ratio was 0.49 (95% CI: 0.32, 0.75); and for a score of 4, the hazard ratio was 0.19 (95% CI: 0.05, 0.75) (P < 0.001 by log-rank test). In conclusion, a combination of regular exercise, healthy diet, smoking avoidance, and weight maintenance was associated with lower coronary calcium incidence, slower calcium progression, and lower all-cause mortality over 7.6 years.

Indices of Cholesterol Metabolism and Relative Responsiveness to Ezetimibe and Simvastatin

CONTEXT The level and duration of exposure to circulating low-density lipoprotein-cholesterol (LDL-C) are major contributors to coronary atherosclerosis. Therefore, optimal prevention will require long-term LDL-C reduction, making it important to select the most effective agent for each individual. OBJECTIVE We tested the hypothesis that individuals with high fractional absorption of cholesterol respond better to the cholesterol absorption inhibitor ezetimibe than to simvastatin, whereas low absorbers, who have elevated rates of cholesterol synthesis, respond better to simvastatin. DESIGN, SETTING, AND PARTICIPANTS A randomized, double-blind, placebo-controlled, crossover trial was performed in 215 African- and European-American men. INTERVENTION Participants were randomized to placebo, ezetimibe (10 mg/d), simvastatin (10 mg/d), and both drugs for 6 wk each. MAIN OUTCOME Plasma levels of LDL-C, surrogate markers for cholesterol absorption (campesterol) and synthesis (lathosterol), and proprotein convertase subtilisin-like kexin type 9 were measured at baseline and after treatment. RESULTS LDL-C levels were reduced by 19% (ezetimibe), 25% (simvastatin), and 41% (ezetimibe+simvastatin) from a baseline of 146 +/- 20 mg/dl; results were similar between ethnic groups. Reduction in LDL-C correlated poorly with baseline levels of noncholesterol sterols and proprotein convertase subtilisin-like kexin type 9. Although individual responses varied widely, change in LDL-C on ezetimibe correlated with response to simvastatin (r = 0.46, P < 0.001). Combination therapy lowered LDL-C by 15% or greater in more than 95% of participants. CONCLUSIONS Baseline cholesterol absorption and synthesis did not predict responsiveness to LDL-lowering drugs. Responsiveness to simvastatin and ezetimibe were highly correlated, suggesting that factors downstream of the primary sites of action of these drugs are a major determinant of response.

Implications of Increased C-Reactive Protein for Cardiovascular Risk Stratification in Black and White Men and Women in the US

BACKGROUND We evaluated prevalence and correlates of increased high-sensitivity C-reactive protein (hsCRP) in a large population of blacks and whites, and the impact of hsCRP measurement on coronary heart disease risk reclassification. METHODS We studied 19 080 participants of the REGARDS (REasons for Geographic And Racial Differences in Stroke) study (age >45 years, without vascular diagnoses, and living dispersed across the US). A total of 8309 nondiabetic participants not using lipid-lowering medications were classified into 4 risk categories based on the Framingham vascular disease risk score. Participants with hsCRP <1 mg/L were reclassified to the next lower risk group, and those with hsCRP >3 mg/L to the next higher risk group. We also assessed reclassification of risk based on the Reynolds vascular risk score, incorporating hsCRP and family history. RESULTS Overall, 40% of participants had hsCRP >3 mg/L. Blacks, women, and obese people were at highest risk for increased hsCRP. Among nondiabetic women at 5%-20% Framingham vascular predicted risk, hsCRP data led to reclassification of 48% to a higher risk group and 19% to a lower risk group. For men, these percentages were 24% and 40%. Blacks were more often reclassified to a higher risk group than whites. Reynolds vascular risk score data led to reclassification of 85% of women and 67% of men, almost exclusively to a lower risk group than the Framingham vascular score. CONCLUSIONS In this national study, a majority of participants, especially blacks and women, were reclassified to a different 10-year vascular risk category on the basis of hsCRP testing after risk assessment. With the inclusion of hsCRP testing data, the Reynolds risk score classified the population differently than the new Framingham vascular score. .

Cardiorespiratory Fitness and Long‐Term Survival in “Low‐Risk” Adults

Background We sought to establish whether cardiorespiratory fitness had important implications for long-term cardiovascular risk among individuals classified as low risk by the Framingham Risk Score (10-year coronary heart disease risk <10%). Prognostic factors of long-term cardiovascular risk are needed for low-risk subjects who make up the largest percentage of the US population. Methods and Results The study population was composed of men and women, 30 to 50 years of age, who had a baseline medical exam at the Cooper Clinic, Dallas, TX, between 1970 and 1983. Eligible individuals were defined as at low risk for coronary heart disease by Framingham Risk Score at the time of study entry and had no history of diabetes (n=11 190). Cardiorespiratory fitness was determined by maximum graded exercise treadmill tests. Over an average 27±2-year period, 15% of low-fit (quintile 1) compared to 6% of high-fit (quintile 5) individuals died (P<0.001). A 1–metabolic equivalent level increase in baseline fitness was associated with an 11% reduction in all-cause deaths and an 18% reduction in deaths due to cardiovascular disease (CVD) after adjustment for age, sex, body mass index, systolic blood pressure, total cholesterol, blood glucose levels, smoking, and early family history of coronary disease. There was an incremental decrease in CVD risk with increasing fitness quintile, such that the high fit had the lowest adjusted 30-year CVD mortality rate (hazard ratio 0.29, 95% CI: 0.16–0.51) compared to the low fit. Conclusions Cardiorespiratory fitness is associated with a significant reduction in long-term CVD among individuals identified as low risk by Framingham Risk Score. These data suggest that preventive lifestyle interventions geared to optimize cardiorespiratory fitness, even among a “low-risk” subset, should be considered to improve CVD-free survival. (J Am Heart Assoc. 2012;1:e001354 doi: 10.1161/JAHA.112.001354.)

The relationship between inflammation, obesity and risk for hypertension in the Multi-Ethnic Study of Atherosclerosis (MESA)

It has been suggested that inflammation is important in the aetiology of hypertension and that this may be most relevant among obese persons. To study this, we examined the independent relationships between obesity, inflammation-related proteins (interleukin-6 (IL-6), C-reactive protein (CRP) and fibrinogen) and risk for hypertension in the Multi-Ethnic Study of Atherosclerosis (MESA). Hypertension status, defined as a blood pressure ⩾140/90 mm Hg or a history of hypertension and use of blood pressure medications, was determined at baseline and two subsequent exams over 5 years. Among 3543 non-hypertensives at baseline, 714 individuals developed incident hypertension by Exam 3. Cox proportional hazard models were used to determine the relationship between baseline levels of IL-6, CRP and fibrinogen and future risk of hypertension. One s.d. difference in baseline concentration of IL-6, CRP or fibrinogen was associated with 20–40% greater risk of incident hypertension. This risk was attenuated after accounting for other hypertension risk factors (hazard ratio (HR) IL-6: 1.13 (95% CI: 1.04–1.23); CRP: 1.11 (95% CI: 1.02–1.21); fibrinogen 1.0 (95% CI: 0.92–1.08)). Conversely, obesity was an independent risk factor for hypertension risk, minimally impacted by other covariates, including IL-6 and CRP (HR 1.72 (95% CI: 1.36–2.16)). IL-6 and CRP did not modify the relationship between obesity and hypertension, though an adjusted twofold greater risk was observed for obese individuals with a CRP >3 mg l−1 compared with CRP <1 mg l−1. The relationship between inflammation-related proteins and hypertension risk was predominantly explained by other hypertension risk factors. Obesity, independent of inflammation, remained a potent risk factor for future hypertension.

Impact of Body Mass Index, Physical Activity, and Other Clinical Factors on Cardiorespiratory Fitness (from the Cooper Center Longitudinal Study)

Cardiorespiratory fitness (CRF) is widely accepted as an important reversible cardiovascular risk factor. In the present study, we examined the nonmodifiable and modifiable determinants of CRF within a large healthy Caucasian population of men and women. The study included 20,239 patients presenting to Cooper Clinic (Dallas, Texas) for a comprehensive medical examination from 2000 through 2010. CRF was determined by maximal treadmill exercise testing. Physical activity categories were 0 metabolic equivalent tasks (METs)/min/week (no self-reported moderate or vigorous intensity physical activity), 1 to 449 METs/min/week (not meeting physical activity guideline), 450 to 749 METs/min/week (meeting guideline), and ≥750 METs/min/week (exceeding guideline). Linear regression modeling was used to determine the most robust clinical factors associated with achieved treadmill time. Age, gender, body mass index (BMI), and physical activity were the most important factors associated with CRF, explaining 56% of the variance (R(2) = 0.56). The addition of all other factors combined (current smoking, systolic blood pressure, blood glucose, high-density and low-density lipoprotein cholesterol, health status) were associated with CRF (p <0.05) but additively only improved R(2) by 2%. There was a significant interaction between BMI and physical activity on CRF, such that normal-weight (BMI <25 kg/m(2)) subjects achieved higher CRF for a given level of physical activity compared to obese subjects (BMI ≥30 kg/m(2)). Percent body fat, not lean body mass, was the key factor driving this interaction. In conclusion, BMI was the most important clinical risk factor associated with CRF other than nonmodifiable risk factors age and gender. For a similar amount of physical activity, normal-weight subjects achieved a higher CRF level compared to obese subjects. These data suggest that obesity may offset the benefits of physical activity on achieved CRF, even in a healthy population of men and women.

Physical activity participation, health perceptions, and cardiovascular disease mortality in a multiethnic population: The Dallas Heart Study

BACKGROUND Physical activity (PA) participation differs by ethnicity, but contributing factors and cardiovascular (CV) outcomes related to these disparities are not well understood. We determined whether health beliefs regarding the benefit of PA contribute to ethnic differences in participation and assessed how these differences impact CV mortality. METHODS The Dallas Heart Study is a longitudinal study of CV health. We assessed PA participation and health perceptions by questionnaire among 3,018 African American, Hispanic, and white men and women at baseline visit (2000-2002). Participant mortality was obtained through 2008 using the National Death Index. RESULTS African Americans (odds ratio 0.65, 95% CI 0.53-0.80) and Hispanics (odds ratio 0.34, 95% CI 0.26-0.45) were less likely to be physically active compared with whites even after accounting for income, educational status, age, sex, body mass index, diabetes, hypertension, and hyperlipidemia. Beliefs regarding the benefits of PA did not contribute to this disparity, as >94% of individuals felt PA was effective in preventing a heart attack across ethnicity. Physical activity participation was associated with a lower risk of all-cause mortality (hazard ratio [HR] 0.66, 95% CI 0.46-0.93) and CV disease death (HR 0.56, 95% CI 0.32-0.97) in multivariable adjusted models. Similar results were seen when restricting to African Americans (CV disease death, HR 0.57, 95% CI 0.31-1.05). CONCLUSIONS Ethnic minorities reported less PA participation, and lack of PA was associated with higher CV mortality overall and among African Americans. Health perception regarding the benefits of PA did not contribute to this difference, indicating there are other ethnic-specific factors contributing to physical inactivity that require future study.