Dietary n-3 polyunsaturated fatty acids (PUFAs) have been proposed to modulate plasma lipids, lipoprotein metabolism, and inflammatory state and to reduce triglyceride (TG) concentrations. The present double-blind, randomized, placebo-controlled, crossover study investigated the effects of n-3 PUFA supplementation at 3 g/d for 8 weeks on the intravascular kinetics of intestinally derived apolipoprotein (apo) B-48-containing lipoproteins in 10 men with type 2 diabetes.
The characteristic features of dyslipidemia that are associated with insulin-resistant states include elevated plasma triglycerides (TG) due to overaccumulation of TG-rich lipoproteins (TRL) of both intestinal (apoB-48) and hepatic origin (apoB-100), low HDL-cholesterol (C) levels, and the formation of small, dense LDL particles [
Ten men with type 2 diabetes as defined by the American Diabetes Association were recruited in Quebec City area to participate in the study. To be included in the study, participants had to have received stable doses of metformin for at least 3 months before randomization. All eligible subjects were required to discontinue their use of lipid-lowering medications for at least 6 weeks before blood sample collection. Subjects with monogenic lipid disorders; type 1 diabetes; insulin treatment; a previous history of cardiovascular disease; a recent history of alcohol or drug abuse; disorders of the hematologic, digestive, or central nervous system; known impairment of renal function; persistent elevations of serum transaminases; uncontrolled diabetes mellitus (HbA1c > 8.5%); or a history of cancer or of any other conditions that may interfere with optimal participation in the study were ineligible. The study was undertaken using a double-blind, randomized, crossover design with two balanced [1 : 1] treatments of 8 weeks each. All subjects received the following in a random order: 5 g/d (5 × 1 g capsules) of fish oil providing 3 g/d of EPA (64%) and DHA (36%) or a control supplementation (5 × 1 g capsules/d of corn and soybean oil). The treatments were separated by a 12-week wash-out period. During a 4-week run-in stabilization period that preceded the treatments, the participants were advised to consume a low-fat diet following the recommendations of the National Cholesterol Education Program, Adult Treatment Panel III. Dietary intake of marine-derived LCn-3PUFA was limited by prohibiting the consumption of fish throughout the entire experimental period, including during the wash-out period. The consumption of alcohol, vitamin supplements, and natural health products was also strictly forbidden throughout the entire experimental period. Fasting blood samples and kinetic studies using primed-constant infusion of deuterated leucine were performed following each phase of treatment. Compliance was assessed by capsule counting. The research protocol was approved by the Laval University Medical Center ethical review committee, and written informed consent was obtained from each subject. This trial was registered at clinicaltrials.gov as
Twelve-hour fasting venous blood samples were obtained from the subjects’ antecubital veins prior to the beginning of the kinetic study. Serum was separated from the blood cells by centrifugation at 2060 g for 10 minutes at 4°C. Plasma lipids and lipoproteins were measured as previously described [
To determine the kinetics of TRL apoB-48 and VLDL apoB-100, the subjects underwent a primed-constant infusion of L-[5,5,5-D3] leucine while they were in a constantly fed state as previously described [
Wilcoxon signed-rank tests were used to compare the effects of n-3 PUFA on the fasting lipid-lipoprotein profile and kinetic parameters. Differences were considered significant at
Table
Characteristics and fasting lipid/lipoprotein profile of the evaluated patients with type 2 diabetes.
Placebo ( |
n-3 PUFA ( |
% |
| |
---|---|---|---|---|
Body weight, kg | 106.1 ± 19.5 | 105.8 ± 21.0 | −0.3 | 0.7 |
Body mass index, kg/m2 | 34.1 ± 5.5 | 34.1 ± 6.1 | — | 0.7 |
Serum | ||||
Cholesterol, mmol/L | 4.68 ± 0.80 | 4.96 ± 0.58 | +6.0 | 0.05 |
Triglycerides, mmol/L | 2.58 ± 1.12 | 2.33 ± 0.94 | −9.7 | 0.05 |
LDL-cholesterol, mmol/L | 2.55 ± 0.72 | 2.86 ± 0.47 | +12.2 | 0.04 |
HDL-cholesterol, mmol/L | 0.95 ± 0.17 | 1.03 ± 0.20 | +8.4 | 0.007 |
Apolipoprotein B, g/L | 1.00 ± 0.19 | 1.03 ± 0.11 | +3.0 | 0.4 |
Apolipoprotein AI, g/L | 1.12 ± 0.18 | 1.15 ± 0.14 | +2.6 | 0.4 |
Glucose homeostasis | ||||
Glucose, mmol/L | 7.3 ± 1.6 | 8.1 ± 2.2 | +11.0 | 0.3 |
Insulin, |
147 ± 86 | 164 ± 109 | +11.9 | 0.6 |
HbA1c | 0.070 ± 0.010 | 0.072 ± 0.011 | +2.9 | 0.1 |
PUFA: polyunsaturated fatty acid.
Mean ± SD; % represents the percentage of difference between the two intervention phases.
Kinetic parameters of apoB-48 in TRL and apoB-100 in VLDL following supplementation with n-3 PUFA in patients with type 2 diabetes.
Placebo ( |
n-3 PUFA ( |
% |
| |
---|---|---|---|---|
TRL apoB-48 | ||||
Pool size, mg | 99 ± 62 | 96 ± 62 | −2.6 | 0.9 |
Fractional catabolic rate, pools/day | 6.9 ± 3.8 | 7.6 ± 2.8 | +10.0 | 0.3 |
Production rate, mg/kg/day | 5.4 ± 3.2 | 6.0 ± 3.8 | +11.1 | 0.7 |
VLDL apoB-100 | ||||
Pool size, mg | 600 ± 258 | 594 ± 321 | −0.9 | 0.9 |
Fractional catabolic rate, pools/day | 6.9 ± 2.3 | 6.9 ± 2.4 | — | 0.9 |
Production rate, mg/kg/day | 35.6 ± 12.6 | 33.9 ± 12.4 | −5.6 | 0.6 |
PUFA: polyunsaturated fatty acid.
TRL: triglyceride-rich lipoproteins.
Mean ± SD; %
In the present study, supplementation with n-3 PUFAs at a dose of 3 g/d for 8 weeks significantly reduced fasting plasma TG levels but increased plasma cholesterol, LDL-C, and HDL-C concentrations in men with type 2 diabetes compared with a placebo. In addition, n-3 PUFA supplementation had no significant effect on the postprandial secretion and clearance of TRL apoB-48 or VLDL apoB-100 in these subjects.
It is well documented that type 2 diabetes is associated with hypertriglyceridemia and elevated levels of apoB-100- and apoB-48-containing lipoproteins [
Although n-3 PUFA supplementation significantly reduced TG levels in a fasting state, postprandial concentrations of VLDL apoB-100 were not significantly different after the two interventions. Our results showed no significant changes in VLDL apoB-100 fractional catabolic and production rates, a finding that contrasts with previous kinetic studies. Nestel et al. [
The impact of n-3 PUFA supplementation on apoB-48 metabolism has been recently investigated. Levy et al. [
This study has several strengths. The relatively large number of participants and the robust study design (double-blind, randomized, crossover) increased our statistical power. Our specific inclusion criteria also limit the variability related to the background care provided. The statistical analyses were undertaken in a blinded fashion and according to the a priori defined plan and hypothesis testing. Our study also shows that n-3 PUFA supplementation had no significant impact of postprandial TRL apoB-48 kinetics but significantly modulated both fasting TG and LDL-C concentrations. Several potential mechanisms could explain these observations. (1) The meals provided during the kinetic study did not contain n-3 PUFAs, and this could have influenced postprandial response and attenuated n-3 PUFA effects on VLDL apoB-100 and TRL apoB-48 secretion. Recent studies have suggested that the effect of the meal may in fact overwhelm the lipid-lowering effect of the n-3 PUFA supplementation [
n-3 PUFA supplementation for 8 weeks was effective at reducing fasting TG levels in subjects with type 2 diabetes but also increased levels of plasma cholesterol, LDL-C, and HDL-C. However, no significant effect was observed on postprandial VLDL apoB-100 and TRL apoB-48 levels or kinetics.
Apolipoprotein
Docosahexaenoic acid
Eicosapentaenoic acid
Glycated hemoglobin
High-density lipoprotein
Low-density lipoprotein
Polyunsaturated fatty acid
Triglyceride-rich lipoprotein
Very-low-density lipoprotein.
Benoît Lamarche is the Chair of Nutrition at Laval University.
All authors declare that they have no relevant conflict of interests.
All of the authors read and approved the final paper. Patrick Couture and Benoît Lamarche designed the research; André J. Tremblay and Jean-Charles Hogue conducted the research; Patrick Couture, Benoît Lamarche, and André J. Tremblay analyzed the data; Patrick Couture, André J. Tremblay, and Benoît Lamarche wrote the paper; and Patrick Couture had primary responsibility for the final content.
The authors are grateful for the excellent cooperation of the subjects and for the dedicated staff at the Institute of Nutrition and Functional Food and Lipid Research Centre. This work was supported by the Canadian Institutes of Health Research (MOP-86488).