Increased Postprandial Triglyceride-Rich Lipoprotein Levels in Elderly Survivors of Myocardial Infarction

High-density lipoproteins (HDL): Novel function and therapeutic applications

The failure of high-density lipoprotein (HDL)-raising agents to reduce cardiovascular disease (CVD) together with recent findings of increased cardiovascular mortality in subjects with extremely high HDL-cholesterol levels provide new opportunities to revisit our view of HDL. The concept of HDL function developed to explain these contradictory findings has recently been expanded by a role played by HDL in the lipolysis of triglyceride-rich lipoproteins (TGRLs) by lipoprotein lipase. According to the reverse remnant-cholesterol transport (RRT) hypothesis, HDL critically contributes to TGRL lipolysis via acquirement of surface lipids, including free cholesterol, released from TGRL. Ensuing cholesterol transport to the liver with excretion into the bile may reduce cholesterol influx in the arterial wall by accelerating removal from circulation of atherogenic, cholesterol-rich TGRL remnants. Such novel function of HDL opens wide therapeutic applications to reduce CVD in statin-treated patients, which primarily involve activation of cholesterol flux upon lipolysis.

Delayed clearance of triglyceride-rich lipoproteins in young, healthy obese subjects

Obesity is associated with the metabolic syndrome. The aims were, first, to study the postprandial triglyceride clearance in young, healthy obese subjects and, second, to investigate if fasting triglycerides can predict delayed postprandial triglyceride clearance. Eighteen apparently healthy, obese subjects with no clinical signs of metabolic disturbances participated. Controls were age- and sex-matched, healthy, normal weight subjects. Subclinical markers of metabolic disturbances were assessed by measuring postprandial triglycerides in serum and in chylomicrons by oral fat tolerance test. Postprandial triglyceride clearance for 8 h was assessed indirectly as removal of the lipid from serum during the oral fat tolerance test. Insulin resistance was measured by the homeostasis model assessment of insulin resistance (HOMA-IR). Twelve (66%) of the apparently healthy obese individuals had insulin resistance measured by HOMA-IR. There was a delayed clearance of serum triglycerides and chylomicron triglycerides at 6 h when compared with the control group, while, at 8 h, the differences were only detected for the chylomicron triglyceride clearance. Triglyceride response was significantly greater in the obese subjects. Fasting triglycerides in upper normal level predicted a delayed postprandial triglyceride clearance and insulin resistance. In young, apparently healthy obese subjects early metabolic disturbances including insulin resistance and delayed postprandial triglyceride clearance can be detected. Fasting serum triglyceride in upper normal level predicted delayed postprandial triglyceride clearance and insulin resistance.

Postprandial lipemia as a cardiometabolic risk factor

High levels of fasting circulating triglycerides (TG) represent an independent risk factor for cardiovascular disease. In western countries, however, people spend most time in postprandial conditions, with continuous fluctuation of lipemia due to increased levels of TG-rich lipoproteins (TRLs), including chylomicrons (CM), very low density lipoproteins (VLDL), and their remnants. Several factors contribute to postprandial lipid metabolism, including dietary, physiological, pathological and genetic factors. The presence of coronary heart disease, type 2 diabetes, insulin resistance and obesity is associated with higher postprandial TG levels compared with healthy conditions; this association is present also in subjects with normal fasting TG levels. Increasing evidence indicates that impaired metabolism of postprandial lipoproteins contributes to the pathogenesis of coronary artery disease, suggesting that lifestyle modifications as well as pharmacological approaches aimed at reducing postprandial TG levels might help to decrease the cardiovascular risk.

Postprandial lipemia is not increased in patients with previous unprovoked venous thromboembolism

BACKGROUND

Patients with arterial cardiovascular disease have increased postprandial lipemia, and plasma levels of postprandial remnants are related to the progression of atherosclerosis. Studies have shown that patients with unprovoked venous thromboembolism have increased risk of arterial cardiovascular disease.

OBJECTIVE

To investigate whether patients with a history of unprovoked venous thromboembolism have increased postprandial lipemia.

METHODS

A population-based case-control study was performed in 20 patients with a history of unprovoked venous thromboembolism and 20 age- and gender-matched healthy controls. Participants were subjected to a standard fat tolerance test (1 g/kilo body weight) with subsequent blood sampling every second hour for 8 hours. Lipids were measured by traditional methods and lipoprotein subclasses by proton nuclear magnetic resonance.

RESULTS

Fasting lipids and lipoprotein subclasses did not differ between groups. The postprandial lipemia, assessed by the incremental area under the triglyceride curve, was not different in venous thromboembolism patients and healthy controls (5.0 ± 3.6 mmol/L∗h vs 5.3 ± 4.4 mmol/L∗h, P = .81). Similarly, the distribution and size of the lipoprotein subclasses obtained 4 hours postprandially did not differ between groups.

CONCLUSION

Patients with a history of unprovoked venous thromboembolism had similar lipoprotein subclasses size, distribution, and postprandial lipemia as healthy controls. Our findings indicate that postprandial lipemia is not a link between unprovoked venous thromboembolism and arterial cardiovascular disease.

Incidence of and risk factors for type-2 diabetes in a general population: The Tromsø Study

Aims: To determine the gender-specific incidence and risk factors of type-2 diabetes mellitus (T2DM) in a general population. Methods: The study is based on 12,431 men and 13,737 women aged 25-98 years, attending the Tromsø Study in 1994 and followed through 2005, who did not have diabetes when entering the study. Sex-specific hazard ratios were estimated from Cox proportional hazard models. Results: A total of 522 cases of T2DM were registered, 308 among men and 214 among women. The age-standardised incidence rate was higher in men than in women, 2.6 (95% CI 2.32—2.90) and 1.6 (95% CI 1.40—1.83) per 1000 person-years, respectively. In multivariate survival analysis, age, body mass index (BMI), triglycerides, high-density lipoprotein (HDL) cholesterol, hypertension, family history of diabetes, low education and smoking were independent predictors of T2DM in both genders (p>0.05). Total cholesterol and lack of leisure-time physical activity were independent predictors in men only. We found an interaction between HDL cholesterol and triglyceride levels (p>0.001) and between triglyceride levels and a positive family history of diabetes (p = 0.04). These interactions were independent of BMI. A positive family history combined with triglycerides in the highest tertile and BMI >25 kg/m2 conveyed a 10-year risk of T2DM of 10% (95% CI 8—12%) vs. 0.2% (95% CI 0.08—0.31%) for the lowest risk group. Conclusions: A family history of diabetes, elevated BMI, and high triglyceride levels identifies independent of cardiovascular risk factors, a group with especially high risk of T2DM.

Dose-response of n-3 polyunsaturated fatty acids on lipid profile and tolerability in mildly hypertriglyceridemic subjects

The n-3 polyunsaturated fatty acids (PUFAs) are known to reduce risk for coronary heart disease partly by altering blood lipids. The purpose of this study was to determine the effect of low doses of n-3 PUFAs on the lipid profile and their tolerability in mildly hypertriglyceridemic subjects. Subjects with a serum triacylglycerol (TG) level between 100 and 300 mg/dL were placed on a corn oil placebo (seven capsules per day; single-blind) for 4 weeks and then randomized to continue seven capsules per day of placebo (n = 49) or one of the following doses of n-3 PUFAs for 20 weeks: 0.5 g (n = 51), 1 g (n = 23), or 2 g (n = 12). During the treatment period, 48-50% of the 1-g and 2-g dose groups reported noticing burping (P < .05), and only about half as many in the 0.5-g group noticed burping. Interestingly, 2% of those assigned to the placebo did report a fishy burping during the study, but this dropped back to nearly 0% by week 20. There was no significant effect for any dosage group on fasting and postprandial serum TG, chylomicron TG, very-low-density lipoprotein-cholesterol, or high-density lipoprotein-cholesterol concentration. However, 1-g and 2-g n-3 PUFA treatments significantly increased total cholesterol and low-density lipoprotein-cholesterol concentration. In addition, all doses of n-3 PUFA treatments significantly increased plasma phospholipid n-3 PUFAs. We conclude that doses of n-3 PUFAs of 0.5-2 g/day in healthy volunteers with above average TG levels did not have beneficial effects on their lipid profiles.

Tissue factor-induced thrombin generation in the fasting and postprandial state among elderly survivors of myocardial infarction

INTRODUCTION

Tissue factor (TF)-induced thrombin generation (TG) ex vivo has been suggested to be an important method to assess thrombotic risk. No studies have investigated the impact of postprandial lipemia on TF-induced TG. Since myocardial infarction (MI) is associated with elevated postprandial levels of triglycerides, we hypothesized a differential impact of postprandial lipemia on coagulation activation in MI-patients and healthy controls.

MATERIAL AND METHODS

Elderly survivors of acute MI (n=44) and healthy age-and sex matched controls (n=43) underwent a fat tolerance test (1 gram per kg body weight) to assess coagulation activation during postprandial lipemia.

RESULTS

The incremental area under the curve (AUCi) for serum triglycerides was higher in MI-patients than in healthy age-and sex matched controls (5.64±0.52 mmol/L*h and 3.94±0.39 mmol/L*h, p=0.012) during the postprandial phase. Subsequent endogenous activation of coagulation, assessed by FVIIa and thrombin generation (F1+2), was similar among groups and not related to levels of triglycerides during the postprandial phase. Healthy individuals had a gradual decline in TF-induced thrombin generation ex vivo, assessed by endogenous thrombin potential (ETP) (AUCi=-542.4±71.4 nM*min*h, p<0.001), whereas MI-patients retained their ETP (AUCi=127.4±89.0 nM*min*h, p=0.47) in plasma during the postprandial phase (p for group difference=0.005).

CONCLUSIONS

MI-patients had elevated postprandial lipemia and retained their ability for TF-induced TG in plasma ex vivo in the postprandial phase, whereas the capacity gradually decreased in healthy individuals. Further studies are warranted to reveal underlying mechanism(s) and clinical implications.