Reduced adipose tissue lipoprotein lipase responses, postprandial lipemia, and low high-density lipoprotein-2 subspecies levels in older athletes with silent myocardial ischemia

Caloric restriction: powerful protection for the aging heart and vasculature

Cardiovascular disease (CVD) is the leading cause of morbidity and mortality in the United States. Research has shown that the majority of the cardiometabolic alterations associated with an increased risk of CVD (e.g., insulin resistance/type 2 diabetes, abdominal obesity, dyslipidemia, hypertension, and inflammation) can be prevented, and even reversed, with the implementation of healthier diets and regular exercise. Data from animal and human studies indicate that more drastic interventions, i.e., calorie restriction with adequate nutrition (CR), may have additional beneficial effects on several metabolic and molecular factors that are modulating cardiovascular aging itself (e.g., cardiac and arterial stiffness and heart rate variability). The purpose of this article is to review the current knowledge on the effects of CR on the aging of the cardiovascular system and CVD risk in rodents, monkeys, and humans. Taken together, research shows that CR has numerous beneficial effects on the aging cardiovascular system, some of which are likely related to reductions in inflammation and oxidative stress. In the vasculature, CR appears to protect against endothelial dysfunction and arterial stiffness and attenuates atherogenesis by improving several cardiometabolic risk factors. In the heart, CR attenuates age-related changes in the myocardium (i.e., CR protects against fibrosis, reduces cardiomyocyte apoptosis, prevents myosin isoform shifts, etc.) and preserves or improves left ventricular diastolic function. These effects, in combination with other benefits of CR, such as protection against obesity, diabetes, hypertension, and cancer, suggest that CR may have a major beneficial effect on health span, life span, and quality of life in humans.

FABP2 Ala54Thr genotype is associated with glucoregulatory function and lipid oxidation after a high-fat meal in sedentary nondiabetic men and women

BACKGROUND

A common functional missense mutation [Ala54Thr of the fatty acid-binding protein 2 gene (FABP2)] has previously been studied for associations with glucoregulation, postprandial lipemia, and lipid oxidation rates. However, most of those studies have not accounted for the interactive and potentially confounding effects of habitual physical activity and diet.

OBJECTIVE

We tested the hypothesis that, in sedentary nondiabetic subjects following a low-fat diet, Thr54 FABP2 carriers have lower glucoregulatory function, greater postprandial lipemia, and greater lipid oxidation rates than do their Ala54 FABP2-homozygous counterparts.

DESIGN

Men and women (n = 122) aged 50-75 y who were following a low-fat diet were genotyped and underwent oral-glucose-tolerance tests. A subgroup (n = 36) also underwent postprandial lipemia tests with lipid oxidation rate measurements.

RESULTS

Thr54 carriers were less likely to have normal glucose tolerance (P = 0.05) and had higher fasting glucose concentrations (P = 0.003) than did Ala54 homozygotes. In Thr54 carriers, the insulin sensitivity index was lower (P = 0.02), and the fasting insulin and the oral-glucose-tolerance test insulin area under the curve were higher (P = 0.05 and 0.03, respectively) than in Ala54 homozygotes. FABP2 genotype was not associated with fasting or postprandial lipemia test triacylglycerol or free fatty acids (P > or = 0.22 for all), but postprandial lipid oxidation rates were higher (P = 0.01), which suggests that fat absorption is higher in Thr54 carriers than in Ala54 homozygotes.

CONCLUSIONS

In sedentary nondiabetic persons following a low-fat diet, FABP2 Thr54 carriers have lower glucose tolerance and lower insulin action than do Ala54-homozygous persons. Furthermore, FABP Thr54 carriers have higher lipid oxidation rates, which may be the mechanism of glucoregulatory dysfunction.

Modification of lipoproteins by very low-carbohydrate diets

Very low-carbohydrate diets (VLCDs) are popular, but remain controversial. This review summarizes the latest studies that have examined the effects of VLCDs on lipoproteins and related risk factors for cardiovascular disease. Prospective studies indicate that VLCDs improve the lipoprotein profile independently of weight loss. Although not as effective at lowering LDL cholesterol (LDL-C), VLCDs consistently improve postabsorptive and postprandial triacylglycerols (TAGs), HDL cholesterol (HDL-C), and the distribution of LDL-C subfractions to a greater extent than low-fat diets. VLCDs also improve proinflammatory markers when associated with weight loss. Studies usually report mean lipid responses, but individual data indicate a large degree of variability in the magnitude and in some cases the direction (e.g., LDL-C) of lipoprotein responses to both low-fat and VLCDs. Such variability makes it hard to defend a single diet recommendation, especially considering the potential for low-fat/high-carbohydrate diets to exacerbate TAG, HDL-C, and other characteristics of the metabolic syndrome. Considering the effectiveness of VLCDs in promoting fat loss and improving the metabolic syndrome, discounting or condemning their use is unjustified. We encourage a more unbiased, balanced appraisal of VLCDs.

Lipoprotein lipase activator NO-1886

Lipoprotein lipase (LPL) is a rate-limiting enzyme that hydrolyzes circulating triglyceride-rich lipoproteins such as very low-density lipoproteins and chylomicrons. A decrease in LPL activity is associated with an increase in plasma triglycerides (TG) and a decrease in plasma high-density lipoprotein cholesterol (HDL-C). The increase in plasma TG and decrease in plasma HDL-C are risk factors for cardiovascular disease. Tsutsumi et al. hypothesized that elevating LPL activity would cause a reduction of plasma TG and an increase in plasma HDL-C, resulting in protection against the development of atherosclerosis. To test this hypothesis, Otsuka Pharmaceutical Factory, Inc. synthesized the LPL activator NO-1886. NO-1886 increased LPL mRNA and LPL activity in adipose tissue, myocardium and skeletal muscle, resulting in an elevation of postheparin plasma LPL activity and LPL mass in rats. NO-1886 also decreased plasma TG concentration and caused a concomitant rise in plasma HDL-C. Long-term administration of NO-1886 to rats and rabbits with experimental atherosclerosis inhibited the development of atherosclerotic lesions in coronary arteries and aortas. Multiple regression analysis suggested that the increase in plasma HDL-C and the decrease in plasma TG protect from atherosclerosis. The atherogenic lipid profile is changed to an antiatherogenic profile by increasing LPL activity, resulting in protection from atherosclerosis. Therefore, the LPL activator NO-1886 or other possible LPL activating agents are potentially beneficial for the treatment of hypertriglyceridemia, hypo-HDL cholesterolemia, and protection from atherosclerosis.

Effects of prior exercise on postprandial lipemia: a quantitative review

The purpose of this report is to synthesize the results from studies examining the effect of exercise on postprandial lipemia to summarize the existing data and provide direction for future research. A quantitative review of the literature was performed using meta-analytic methods to quantify the effect sizes. Moderator analyses were performed to examine features of the studies that could potentially influence the effect of exercise on postprandial lipemia. Thirty-eight effects from 555 people were retrieved from 29 studies. The mean weighted effect was moderate as indicated by Cohen's d (d = -0.57; 95% confidence interval [CI], -0.71 to -0.43), indicating that people who perform exercise before meal ingestion exhibit a 0.5 standard deviation reduction in the postprandial triglyceride (TG) response relative to persons in comparison groups. There was no significant effect of study design, gender, age, type of meal ingested, exercise intensity, exercise duration, or timing of exercise on the postprandial response (P >.05). There was, however, significant variation in the effect sizes, for women for exercise performed within 24 hours of meal ingestion, and for exercise performed more than 24 hours before meal ingestion (P <.01). For studies that reported the energy expenditure of exercise, there was a significant relationship between effect size and energy expenditure (r = -.62, P =.02). Results from this quantitative review of the literature suggest that exercise has a moderate effect on the postprandial lipemic response and that the energy expenditure of prior exercise may play a role in the magnitude of this effect. Other factors that may affect the response remain to be clarified.

Postprandial triglyceride response in patients with polycystic ovary syndrome: relationship with waist-to-hip ratio and insulin

OBJECTIVE

To examine the postprandial triglyceride response to a high-fat meal in women with polycystic ovary syndrome (PCOS) compared with a matched control group.

DESIGN

Controlled clinical study.

SETTING

Department of Endocrinology and Pathophysiology, School of Medicine, Universidad de Los Andes.

PATIENT(S)

18 Hispanic women with PCOS (nine overweight and nine nonobese) and 9 healthy control women.

INTERVENTION(S)

Biometric measures and blood sample collection.

MAIN OUTCOME MEASURE(S)

Insulin and glucose levels during a standard oral glucose tolerance test. Plasma triglyceride, cholesterol, and high-density lipoprotein cholesterol levels were measured at baseline and at 4, 5, and 6 h after a high-fat meal.

RESULT(S)

Both obese and nonobese PCOS women had higher waist-to-hip ratios than controls. PCOS women had higher levels of fasting and postglucose insulin and fasting triglyceride and postprandial triglyceride response and had lower levels of postprandial high-density lipoprotein cholesterol response, but no significant differences within PCOS groups were observed.

CONCLUSION(S)

An expanded postprandial hypertriglyceridemia in PCOS women is related to a higher waist-to-hip ratio and insulin resistance, regardless of obesity, and contributes to increase the risk for coronary artery disease.

Fasting lipoprotein and postprandial triacylglycerol responses to a low-carbohydrate diet supplemented with n-3 fatty acids

BACKGROUND

The effects of a prolonged low-carbohydrate diet rich in n-3 fatty acids on blood lipid profiles have not been addressed in the scientific literature.

OBJECTIVE

This study examined the effects of an eight-week ketogenic diet rich in n-3 fatty acids on fasting serum lipoproteins and postprandial triacylglycerol (TG) responses.

DESIGN

Ten men consumed a low-carbohydrate diet rich in monounsaturated fat (MUFA) and supplemented with n-3 fatty acids for eight weeks. Fasting blood samples were collected before and after one week of habitual diet and on two consecutive days after 2, 4, 6 and 8 weeks of the intervention diet. Postprandial TG responses to a fat-rich test meal were measured prior to and after the intervention diet.

RESULTS

Compared to the habitual diet, subjects consumed significantly (p < or = 0.05) greater quantities of protein, fat, MUFA and n-3 fatty acids and significantly less total energy, carbohydrate and dietary fiber. Body weight significantly declined over the experimental period (-4.2+/-2.7 kg). Compared to baseline, fasting total cholesterol, LDL cholesterol and HDL cholesterol were not significantly different after the intervention diet (+1.5%, +9.7% and +10.0%, respectively). Fasting TG were significantly reduced after the intervention diet (-55%). There was a significant reduction in peak postprandial TG (-42%) and TG area under the curve (-48%) after the intervention diet.

CONCLUSIONS

A hypocaloric low-carbohydrate diet rich in MUFA and supplemented with n-3 fatty acids significantly reduced postabsorptive and postprandial TG in men that were not hypertriglyceridemic as a group before the diet. This may be viewed as a clinically significant positive adaptation in terms of cardiovascular risk status. However, transient increases in total cholesterol and LDL cholesterol were also evident and should be examined further in regard to which particular subfractions are elevated.

Postprandial lipoprotein metabolism and atherosclerosis

Postprandial lipids and lipoproteins have been associated with the presence of cardiovascular disease in a large number of case-control studies. Because the metabolic perturbations around the postprandial situation is a key driving force for cholesterol flux between lipoproteins and tissues, together with the augmented generation of potentially atherogenic cholesterol-rich remnant lipoproteins, several hypotheses have been formulated to link excessive lipoproteinaemic response to fat intake with cardiovascular disease. Recent information on the regulation of lipoprotein remnant formation and its relation to atherosclerosis will enable us to test a pertinent clinical question: is there a direct relationship between repeated elevations of postprandial lipoproteins and development of atherosclerosis?

Effect of apo E phenotype on plasma postprandial triglyceride levels in young male adults with and without a familial history of myocardial infarction: the EARS II study. European Atherosclerosis Research Study

The goal of the present study was to assess whether the effect of the apolipoprotein E polymorphism on postprandial lipemia explained part of the risk attributable to familial history of coronary heart disease. Cases (n = 407) were students, aged between 18 and 28 years, whose fathers had a proven myocardial infarction before the age of 55 years. Age-matched controls (n = 415) were recruited from the corresponding student registers. Blood was obtained after an overnight fast and at 2, 3, 4 and 6 h after ingestion of a fatty meal for triglyceride measurements. Apolipoprotein E phenotype was associated with postprandial triglyceride variability in both cases and controls. However, the apolipoprotein E-dependent triglyceride response was not significantly heterogeneous between cases and controls. In the pooled data, postprandial triglyceride levels were higher in carriers of the E2 and, to a lesser extent, of the E4 isoform, than in E3/3 homozygotes, independently of fasting triglyceride levels. At 6 h, triglyceride levels were increased by 21.2% (P < 0.01) in E2 carriers and 11.5% (P = 0.053) in E4 carriers by comparison to E3/3 subjects. These effects were not significantly different between regions. In conclusion, the effects of the apolipoprotein E polymorphism on postprandial triglyceridemia are similar across regions of Europe, and homogeneous in healthy young subjects with and without a family history of early myocardial infarction. This suggests that the influence of apolipoprotein E on myocardial infarction risk may be acting through mechanisms other than through effects on postprandial triglyceridemia.

Predictors of adipose tissue lipoprotein lipase in middle-aged and older men: relationship to leptin and obesity, but not cardiovascular fitness

The effects of long-term endurance exercise training, body composition, and cardiovascular fitness (VO2max) on the activity of adipose tissue lipoprotein lipase (AT-LPL) and lipoprotein lipids were examined in 66 healthy age-matched middle-aged and older men (mean +/- SE, 61 +/- 1 years). We compared subcutaneous abdominal (ABD) and gluteal (GLT) heparin-elutable AT-LPL activity in 19 master athletes (VO2max > 40 mL/kg/min) and 20 lean sedentary men (VO2max < 40 mL/kg/min) versus 27 obese sedentary men (VO2max < 40 mL/kg/min; body fat > 27%). Fasting insulin and leptin levels were similar in master athletes and lean sedentary men, but were lower than in obese sedentary men. There were no differences in fasting values for total cholesterol or low-density lipoprotein cholesterol (LDL-C) among the groups, but master athletes had lower triglyceride (TG) values (P < .05) and higher high-density lipoprotein cholesterol (HDL-C) and HDL2-C (P < .05) than obese and lean sedentary men. There were no regional (ABD v GLT) differences in the activity of AT-LPL in these groups, but obese sedentary men had higher levels of ABD AT-LPL (2.1 +/- 0.3 nmol/10(6) cells x min) than lean sedentary men (0.8 +/- 0.2) and master athletes (0.5 +/- 0.1, P = .01). Similar results were observed for GLT AT-LPL. Both ABD and GLT AT-LPL activity correlated positively with percent body fat (r = .46 to .54, P < .001), fasting insulin (r = .37 to .45, P < .001), and leptin (r = .61 to .65, P < .0001), but not with VO2max. In stepwise multiple regression analysis, leptin was the main independent predictor of ABD (R2 = .43, P < .0001) and GLT (R2 = .40, P < .0001) AT-LPL activity. Plasma TG correlated positively (r = .32, P < .01) and HDL-C correlated negatively (r = -.32, P = .02) with ABD AT-LPL activity, but these relationships were not significant after controlling for percent body fat or leptin. The results of this study indicate that in healthy middle-aged and older men, the major determinants of AT-LPL activity are obesity and its major associated hormones, leptin and insulin, not cardiovascular fitness, and also suggest that the higher HDL-C levels observed in endurance-trained men are not associated with increased AT-LPL activity.

Exercise-induced silent myocardial ischemia in master athletes

High-physical activity levels are associated with reduced risk of symptomatic coronary artery disease (CAD). However, there are a number of reports of exercise-related sudden death and myocardial infarction in aerobically trained athletes. This study compared the prevalence of exercise-induced silent myocardial ischemia on maximum graded exercise tests with tomographic thallium scintigraphy in 70 master male athletes (63 +/- 6 years, mean +/- SD) (maximum aerobic capacity, VO2max >40 ml/kg/min) and in 85 healthy untrained men (61 +/- 7 years) with no history of CAD. The prevalence of silent ischemia (exercise-induced ST-segment depression on electrocardiogram and perfusion abnormalities on thallium scintigraphy) was similar in athletes and untrained men; 16% of the athletes (11 of 70) had silent ischemia compared with 21% of the untrained men (chi-square = 0.81, p = 0.36). No athletes had hyperlipidemia, systemic hypertension, or diabetes mellitus. However, the apolipoprotein E4 allele was present in 9 of the 11 athletes with silent ischemia compared with 2 of 32 athletes with normal exercise tests (chi-square = 24, p = 0.0001). These results suggest that older male athletes with the apolipoprotein E4 allele are at increased risk for the development of exercise-induced silent ischemia.

Postmortem lipid levels for the analysis of risk factors of sudden death: usefulness of the Ektachem and Monarch analyzers

Elevated serum cholesterol, triglyceride, and free fatty acid levels have been identified as risk factors for sudden death from cardiovascular disease and increased risk for myocardial ischemia or arrhythmias; therefore, correlation of antemortem and postmortem lipid levels may be useful in establishing the cause, pathophysiology, or familial risk factors of sudden death. In the present study, antemortem (within 72 h) and postmortem (within 24 h) cholesterol, triglyceride, free fatty acid, and albumin levels were analyzed in seven autopsied hospitalized patients from the University of New Mexico Hospital in Albuquerque, New Mexico. The cholesterol, triglyceride, and albumin levels were measured by dry-slide technology on an Ektachem 700 analyzer, and the free fatty acid levels were measured on a Monarch analyzer with a commercially available kit from Wako Chemical. Postmortem cholesterol levels averaged 13% lower than antemortem levels, postmortem triglyceride levels averaged 38% higher than antemortem levels, postmortem free fatty acid levels averaged 23% lower than antemortem levels, and postmortem albumin levels were essentially unchanged (<0.01% higher) from antemortem levels. Whether the antemortem and postmortem differences in lipid levels were the result of postmortem degradation products, a general phenomenon (such as variable enzyme degradation), or an idiosyncracy of the Ektachem or Monarch systems could not be definitely established. These preliminary results suggest that caution should be exercised when interpreting postmortem cholesterol, triglyceride, and free fatty acid levels analyzed on the Ektachem or Monarch systems.

Effects of low and moderate intensity treadmill walking on postprandial lipaemia in healthy young adults

We have previously shown that the lipaemic response to a fatty meal was reduced when prolonged (2 h) low intensity exercise was taken some hours before eating. The purpose of this study was to test the hypothesis that the effect is quantitatively greater after exercise of moderate intensity than after exercise at low intensity. Six men and six women, mean age 26.9 (SEM 1.5) years, took part in three trials, each conducted over 2 days; on the afternoon of day 1 of each of two exercise trials the subjects walked on a treadmill for 90 min at either 31 (SEM 1) % or 61 (SEM 1) % of maximal oxygen uptake, i.e. low and moderate intensity, respectively; on the control trial the subjects refrained from exercise on day 1. On the morning of day 2 of each trial they ingested a test meal (1.28 g fat, 1.44 g carbohydrate, 76 kJ energy.kg-1 body mass); blood samples were obtained in the fasted state and for 6 h after the meal. Fasting serum triacylglycerol concentration and the area under the postprandial triacylglycerol-time curve were lower than in the control trial (P < 0.05) after moderate intensity walking but not after low intensity walking. The results suggest that the mitigation of the lipaemic response to a meal high in fat and carbohydrate is related to the intensity and/or the energy expenditure of the preceding exercise.