Kinetics of plasma apolipoprotein C-III as a determinant of diet-induced changes in plasma triglyceride levels

OBJECTIVE

To compare the effect of a high monounsaturated fatty acid (MUFA) diet and of a control low-fat diet consumed under ad libitum conditions on plasma apolipoprotein (apo) C-III metabolism.

DESIGN

Randomized, two-arm parallel dietary trial.

SETTING

Diets were prepared and consumed at the metabolic kitchen of the Department of Food Sciences and Nutrition, and laboratory analyses were performed at the Institute of Nutraceuticals and Functional Foods at Laval University.

SUBJECTS AND INTERVENTIONS

Eighteen men were randomly assigned to either the high MUFA diet or the low-fat control diet, which they consumed for 6-7 weeks. Before and after the dietary intervention, subjects received a primed-constant infusion of [5,5,5-D(3)]-L-leucine for 12 h under constant feeding conditions for the determination of plasma apoC-III kinetics.

RESULTS

The high-MUFA diet and the low-fat control diet had no significant impact on plasma apoC-III production rate (PR) or fractional catabolic rate. However, diet-induced variations in plasma apoCIII PR predicted the reduction in plasma triglycerides and apoC-III levels (r=0.85, P<0.01 and r=0.73, P<0.05, respectively) in the high MUFA group only.

CONCLUSIONS

These results suggest that the hypotriglyceridemic effect of a high-MUFA diet may be attributable in part to a reduced hepatic production of apoC-III.

SPONSORSHIP

This study was supported in part by an operating grant from the Canadian Institutes of Health Research (CIHR), and the Canada Research Chair in Nutrition and Cardiovascular Health (B Lamarche).

Effect of obesity on HDL and LDL particle sizes in carriers of the null P207L or defective D9N mutation in the lipoprotein lipase gene: the Québec LipD Study

BACKGROUND

We have recently demonstrated that French Canadians bearing a mutation in the lipoprotein lipase (LPL) gene present an impaired lipoprotein-lipid profile characterized by small low-density lipoprotein (LDL) and high-density lipoprotein (HDL) particles compared with healthy subjects. It has also been documented that obesity has a significant impact on HDL and LDL particle sizes.

OBJECTIVE

To examine the extent to which obesity modulates HDL and LDL particle sizes among carriers of mutations in the LPL gene.

SUBJECTS

Analyses were carried out in 206 heterozygous carriers of the D9N mutation (N=118) or the P207L mutation (N=88).

MEASUREMENTS

Lipoprotein particle sizes were measured on whole plasma by nondenaturing polyacrylamide gradient gel electrophoresis.

RESULTS

In general, body mass index (BMI) and waist circumference were significant correlates of LDL and HDL particle sizes among heterozygous carriers of the P207L or D9N mutation in the LPL gene, with relatively similar associations among men and women. Multivariate analyses indicated that variations in waist circumference but not BMI were an independent predictor of variations in both HDL particle size (5.2%, P=0.0005) and LDL particle size (5.9%, P=0.01) in the entire group of heterozygotes for LPL mutation in a model that included the nature of the LPL mutation (D9N vs P207L), gender, age, cholesterol and plasma TG levels. Interestingly, there was a significant interaction between plasma TG levels and waist circumference or BMI in modulating HDL particle size. Indeed, an increased waist circumference or BMI was associated with a significant reduction in HDL particle size among subjects with plasma TG levels <or=3.5 mmol/l, but not among those with marked hypertriglyceridemia (TG levels >3.5 mmol/l).

CONCLUSION

These results suggest that abdominal obesity, more so that overall obesity, is an important determinant of variations in LDL and HDL particle size among heterozygous carriers of mutations in the LPL gene, perhaps further contributing to modulate the risk of CHD in these individuals.

Comparison of various electrophoretic characteristics of LDL particles and their relationship to the risk of ischemic heart disease

BACKGROUND

Several cross-sectional studies and 3 prospective, nested, case-control studies have indicated that individuals with small, dense low density lipoprotein (LDL) particles are at increased risk for ischemic heart disease (IHD). However, whether LDL particle size is an independent risk factor for future IHD events remains controversial. The objective of the present study was to further analyze the cardiovascular risk associated with various electrophoretic characteristics of LDL particles in men.

METHODS AND RESULTS

LDL particles were characterized by polyacrylamide gradient gel electrophoresis (PAGGE) in a cohort of 2034 men of the Quebec Cardiovascular Study. All men were initially free of IHD and were followed up for a period of 5 years, during which 108 first IHD events were recorded. Among all LDL characteristics investigated by PAGGE, including LDL peak particle size, the cholesterol concentration in LDL particles with a diameter smaller than 255 A showed the strongest association with the risk of IHD (relative risk=4.6 in men in the third vs first tertile of the distribution, P<0.001). Multivariate logistic and survival models indicated that the relationship between LDL cholesterol levels in particles with a diameter <255 A and IHD risk was independent of all nonlipid risk factors and of LDL cholesterol, high density lipoprotein cholesterol, triglyceride, and lipoprotein(a) levels.

CONCLUSIONS

Results from this large, population-based, prospective study suggest that further characterization of LDL particles by PAGGE, in addition to the traditional lipid profile, may improve our ability to predict IHD events in men.

A prospective, population-based study of low density lipoprotein particle size as a risk factor for ischemic heart disease in men

BACKGROUND

The current interpretation of the increased risk of ischemic heart disease (IHD) associated with reduced low density lipoprotein (LDL) particle size is based entirely on data derived from relatively small case-control studies, with a lack of evidence from large, prospective, population-based cohort data.

OBJECTIVES

To investigate the association between LDL particle size and incident IHD on the basis of data from the entire population-based, prospective cohort of men from the Quebec Cardiovascular Study.

PATIENTS AND METHODS

Analyses were conducted in a cohort of 2057 men who were all initially free of IHD, and who were followed up over a five-year period, during which 108 first IHD events (myocardial infarction, angina or coronary death) were recorded. LDL particle size was measured by nondenaturing gradient gel electrophoresis.

RESULTS

Cox proportional hazards analysis indicated that the relationship between LDL particle size and the risk of future IHD events was not linear. Men with an LDL particle size less than 256.0 A had a significant 2.2-fold increase in the five-year rate of IHD (P<0.001) compared with men having an LDL particle size greater than 256.0 A. Multivariate and subgroup analyses indicated that small, dense LDL particles predicted the rate of IHD independent of LDL cholesterol, triglycerides, high density lipoprotein (HDL) cholesterol, apolipoprotein B and the total cholesterol to HDL cholesterol ratio. Finally, the magnitude of the increase in IHD risk attributed to lipid risk factors was modulated to a significant extent by variations in LDL particle size.

CONCLUSIONS

The present study provides the first large scale, population-based, prospective evidence supporting the hypothesis that small, dense LDL particles may be associated with an increased risk of IHD. The results also suggest that information on LDL diameter may improve the ability to predict IHD risk accurately over traditional lipid variables.