Dietary fish oil decreases low-density-lipoprotein clearance in nonhuman primates

Distinct regulation of plasma LDL cholesterol by eicosapentaenoic acid and docosahexaenoic acid in high fat diet-fed hamsters: participation of cholesterol ester transfer protein and LDL receptor

Despite established anti-atherogenic action, previous reports have shown that fish oils or n-3 poly-unsaturated fatty acid (PUFA) increase plasma LDL-C in animals and humans. However, which component of n-3 PUFAs and what mechanisms contribute to this increase are unclear. We investigated the effects of the major components of n-3 PUFA, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), on plasma LDL-C in high fat diet-fed hamsters. While LDL-C increased significantly with n-3 PUFA oil and DHA, EPA had no effect on LDL-C. Interestingly, a positive correlation was found between plasma cholesterol ester transfer protein (CETP) activity and LDL-C. Only DHA increased plasma CETP activity and significantly decreased LDL receptor expression in the liver. Our data suggest that DHA, not EPA, is a major factor in the LDL-C increasing effect of n-3 PUFA oil. These differential effects on LDL-C may arise from differences in plasma CETP activity and LDL receptor expression.

Effects of eicosapentaenoic acid and docosahexaenoic acid on low-density lipoprotein cholesterol and other lipids: a review

In this exploratory, hypothesis-generating literature review, we evaluated potentially differential effects of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) on low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), triglycerides (TG), and non-HDL-C in published studies of ω-3 fatty acid supplementation or prescription ω-3 fatty acid ethyl esters. Placebo-adjusted changes in mean lipid parameters were compared in randomized, controlled trials in subjects treated for ≥ 4 weeks with DHA or EPA. Of 22 studies identified, 6 compared DHA with EPA directly, 12 studied DHA alone (including 14 DHA-treated groups), and 4 examined EPA alone. In studies directly comparing EPA with DHA, a net increase in LDL-C of 3.3% was observed with DHA (DHA: +2.6%; EPA: -0.7%). In such head-to-head comparative studies, DHA treatment was associated with a net decrease in TG by 6.8% (DHA: -22.4%; EPA: -15.6%); a net increase in non-HDL-C by 1.7% (DHA: -1.2%; EPA -2.9%); and a net increase in HDL-C by 5.9% (DHA: +7.3%; EPA: +1.4%). Increases in LDL-C were also observed in 71% of DHA-alone groups [with demonstrated statistical significance (P < .05) in 67% (8 of 12) DHA-alone studies] but not in any EPA-alone studies. Changes in LDL-C significantly correlated with baseline TG for DHA-treated groups. The range of HDL-C increases documented in DHA-alone vs EPA-alone studies further supports the fact that HDL-C is increased more substantially by DHA than EPA. In total, these findings suggest that DHA-containing supplements or therapies were associated with more significant increases in LDL-C and HDL-C than were EPA-containing supplements or therapies. Future prospective, randomized trials are warranted to confirm these preliminary findings, determine the potential effects of these fatty acids on other clinical outcomes, and evaluate the generalizability of the data to larger and more heterogeneous patient populations.

Omega-3 polyunsaturated fatty acids (PUFA) for type 2 diabetes mellitus

BACKGROUND

People with type 2 diabetes mellitus are at increased risk from cardiovascular disease. Dietary omega-3 polyunsaturated fatty acids (PUFAs) are known to reduce triglyceride levels, but their impact on cholesterol levels, glycemic control and vascular outcomes are not well known.

OBJECTIVES

To determine the effects of omega-3 PUFA supplementation on cardiovascular outcomes, cholesterol levels and glycemic control in people with type 2 diabetes mellitus.

SEARCH STRATEGY

We carried out a comprehensive search of The Cochrane Library, MEDLINE, EMBASE, bibliographies of relevant papers and contacted experts for identifying additional trials.

SELECTION CRITERIA

All randomised controlled trials were included where omega-3 PUFA supplementation or dietary intake was randomly allocated and unconfounded in people with type 2 diabetes. Authors of large trials were contacted for missing information.

DATA COLLECTION AND ANALYSIS

Trials were assessed for inclusion. Authors were contacted for missing information. Data was extracted and quality assessed independently in duplicate. Fixed-effect meta-analysis was carried out.

MAIN RESULTS

Twenty three randomised controlled trials (1075 participants) were included with a mean treatment duration of 8.9 weeks. The mean dose of omega-3 PUFA used in the trials was 3.5 g/d. No trials with vascular events or mortality endpoints were identified. Among those taking omega-3 PUFA triglyceride levels were significantly lowered by 0.45 mmol/L (95% confidence interval (CI) -0.58 to -0.32, P < 0.00001) and VLDL cholesterol lowered by -0.07 mmol/L (95% CI -0.13 to 0.00, P = 0.04). LDL cholesterol levels were raised by 0.11 mmol/L (95% CI 0.00 to 0.22, P = 0.05). No significant change in or total or HDL cholesterol, HbA1c, fasting glucose, fasting insulin or body weight was observed. The increase in VLDL remained significant only in trials of longer duration and in hypertriglyceridemic patients. The elevation in LDL cholesterol was non-significant in subgroup analyses. No adverse effects of the intervention were reported.

AUTHORS' CONCLUSIONS

Omega-3 PUFA supplementation in type 2 diabetes lowers triglycerides and VLDL cholesterol, but may raise LDL cholesterol (although results were non-significant in subgroups) and has no statistically significant effect on glycemic control or fasting insulin. Trials with vascular events or mortality defined endpoints are needed.

Microalgal docosahexaenoic acid decreases plasma triacylglycerol in normolipidaemic vegetarians: a randomised trial

Triacylglycerol (TG) lowering effects ofn−3 long-chain PUFA (n−3 LCPUFA) have been repeatedly demonstrated, but studies investigating the individual effects of EPA or DHA on plasma TG and lipoproteins in man are rare. The effects of a new DHA-rich, almost EPA-free microalgae oil (Ulkeniasp.) on plasma lipids and several safety parameters were investigated in a double-blind, placebo-controlled, parallel design intervention study. Normolipidaemic vegetarians (eighty-seven females, twenty-seven males) consumed daily microalgae oil (0·94g DHA/d) or olive oil (as placebo) for 8 weeks. DHA supplementation decreased plasma TG by 23% from 1·08 (sem 0·07) to 0·83 (sem 0·04) mmol/l (p<0·001). Absolute TG decreases after DHA supplementation were inversely correlated to baseline TG concentrations (r−0·627,p<0·001). Plasma total, LDL and HDL cholesterol increased significantly in the DHA group, resulting in lower TG:HDL cholesterol and unchanged LDL:HDL and total cholesterol:HDL cholesterol ratios. The intake of DHA-rich microalgae oil did not result in any physiologically relevant changes of safety and haemostatic factors. In conclusion, DHA-rich oil from microalgaeUlkeniasp. was well tolerated and can be considered a suitable vegetarian source ofn−3 LCPUFA. Although DHA supplementation improved some CHD risk factors (plasma TG, TG:HDL cholesterol ratio), LDL cholesterol increased. Therefore, the overall effects of this intervention on CHD risk deserve further investigation.

Effect of n-3 fatty acids on metabolism of apoB100-containing lipoprotein in type 2 diabetic subjects

The effect of long-chain n-3 PUFA on the metabolism of apoB100-containing lipoprotein in diabetic subjects is not fully understood. The objective of the present study was to determine the effect of a daily intake of 1080 mg EPA and 720 mg DHA for diabetic subjects on the kinetics of apoB100-containing lipoprotein in the fasting state. A kinetic study was undertaken to determine the mechanisms involved in the effects of n-3 fatty acids in terms of a decrease in triacylglycerol level in type 2 diabetic patients. We have studied the effect of fish oils on the metabolism of apoB100 endogenously labelled by [5,5,5-2H3]-leucine in type 2 diabetic patients in the fasting state. The kinetic parameters of apoB100 in VLDL, intermediate-density lipoprotein and LDL were determined by compartmental modelling in five diabetic subjects before and 8 weeks after n-3 fatty acid treatment. Treatment did not change the plasma cholesterol level (0.801 (sd 0.120) v. 0.793 (sd 0.163) mmol/l) but lowered the plasma triacylglycerol level (1.776 (sd 0.280) v.1.356 (sd 0.595) mmol/l; P < 0.05). Treated patients showed a decrease in VLDL apoB100 concentration (0.366 (sd 0.030) v.0.174 (sd 0.036) g/l; P < 0.05) related to a decrease in VLDL 1 production (1.49 (sd 0.23) v.0.44 (sd 0.19) mg/kg per h; P < 0.05) and an increase in the VLDL conversion rate (0.031 (sd 0.024) v.0.052 (sd 0.040) per h; P < 0.05), with no change in fractional catabolic rates. Treatment led to a higher direct production of intermediate-density lipoprotein (0.02 (sd 0.01) v.0.24 (sd 0.12) mg/kg per h; P < 0.05). In conclusion, the present study, conducted in the fasting state, showed that supplementation with n-3 fatty acids in type 2 diabetic patients induced beneficial changes in the metabolism of apoB100-containing lipoprotein.

LDL cholesterol-raising effect of low-dose docosahexaenoic acid in middle-aged men and women

BACKGROUND

Long-chain n-3 polyunsaturated fatty acids have variable effects on LDL cholesterol, and the effects of docosahexaenoic acid (DHA) are uncertain.

OBJECTIVE

The objective of the study was to determine the effect on blood lipids of a daily intake of 0.7 g DHA as triacylglycerol in middle-aged men and women.

DESIGN

Men and women aged 40-65 y (n = 38) underwent a double-blind, randomized, placebo-controlled, crossover trial of treatment with 0.7 g DHA/d for 3 mo.

RESULTS

DHA supplementation increased the DHA concentration in plasma by 76% (P < 0.0001) and the proportion in erythrocyte lipids by 58% (P < 0.0001). Values for serum total cholesterol, LDL cholesterol, and plasma apolipoprotein B concentrations were 4.2% (0.22 mmol/L; P = 0.04), 7.1% (0.23 mmol/L; P = 0.004), and 3.4% (P = 0.03) higher, respectively, with DHA treatment than with placebo. In addition, the LDL cholesterol:apolipoprotein B ratio was 3.1% higher with DHA treatment than with placebo (P = 0.04), which suggested an increase in LDL size. Plasma lathosterol and plant sterol concentrations were unaffected by treatment.

CONCLUSION

A daily intake of approximately 0.7 g DHA increases LDL cholesterol by 7% in middle-aged men and women. It is suggested that DHA down-regulates the expression of the LDL receptor.

A fish oil diet produces different degrees of suppression of apoB and triglyceride secretion in human apoB transgenic mouse strains

Human apolipoprotein B (apoB) transgenic (HuBTg) mouse strains were used to assess genetic effects on the response to fish oil (FO), a source of n-3 fatty acids. A congenic HuBTg strain of the C57BL/6 (B6) background and six F1 HuBTg strains were fed a FO for 2 weeks. Different responses of plasma lipid levels to FO were observed among these strains. In particular, plasma apoB levels changed minimally in FO-fed male B6 HuBTg mice, but increased markedly ( approximately 40%) in FO-fed male FVB/NJ (FVB) x B6 F1 HuBTg mice. These strain differences were determined mainly by hepatic apoB secretion rates and were likely regulated by posttranscriptional mechanisms. In addition, plasma triglyceride (TG) levels were reduced (14%) in FO-fed B6 mice, but not in FVB x B6 mice. These strain differences were determined mainly by TG secretion rates, but were not due to differences in hepatic lipogenesis. Hepatic mRNA levels of acyl-CoA oxidase, reflective of peroxisomal beta-oxidation rate, were increased in FO-fed B6 but not in FVB x B6 mice, which could account for the difference in TG secretion rates. In summary, differential effects of FO on plasma apoB and TG levels in B6 and FVB x B6 HuBTg mice were associated with strain differences in hepatic apoB and TG secretion and in peroxisomal beta-oxidation.

Influence of fish consumption on the distribution of serum cholesterol in lipoprotein fractions: comparative study among fish-consuming and non-fish-consuming populations

The objective of this study was to investigate serum lipoprotein levels in order to assess cardiovascular disease (CVD) risk factors between fish-consuming populations and non-fish-consuming populations, as it has been speculated that fish intake reduces CVD risk. A representative sample of one thousand subjects (529 men and 471 women) were selected, with ages ranging from 20 to 70 years, from 40 villages belonging to fish-consuming (500) or non-fish-consuming (500) populations. Serum lipoprotein lipids such as total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C) and low-density lipoprotein cholesterol (LDL-C) were analysed biochemically using standard procedures. The ratios of TC: HDL-C and LDL-C: HDL-C were computed. Mean values of serum LDL-C and the ratios of LDL-C: HDL-C and TC: HDL-C were significantly lower and HDL-C levels were higher in fish-consumers than in non-fish-consumers. The concentrations of HDL-C decreased with increasing age, while the reverse was true for LDL-C and for the LDL-C: HDL-C and TC: HDL-C ratios. There were significant sex differences for certain age groups in both of the population groups. The 5th, 50th and 95th percentile cut-off values for these parameters were lower in fish-consumers than in non-fish-consumers. The prevalence of individuals at risk of CVD because of low HDL-C (<35 mg/dL), high LDL-C (>130 mg/dL) and their atherogenic ratios (LDL-C: HDL-C >3.5 and TC: HDL-C>4.5) was significantly greater in non-fish-consumers. This study highlights that the fish-consuming population had a lower atherogenic risk than the non-fish-consuming population. The intake of fish may have substantial implications for public health and health economy by decreasing the risk of CVD. However, more studies are warranted to better define the mechanisms of cardioprotection by dietary fish and fish oils.

Long-term melatonin administration increases polyunsaturated fatty acid percentage in plasma lipids of hypercholesterolemic rats

This study was designed to investigate the effect of melatonin on the fatty acid composition of plasma and tissue lipids. Melatonin administration to rats fed with a standard diet only increased long-chain n-6 polyunsaturated fatty acids (PUFA) in total plasma lipids and liver phospholipids but induced significant changes in hypercholesterolemic rats. In plasma, palmitoleic and oleic acids increased and n-6 and n-3 PUFA decreased in hypercholesterolemic rats; theses changes were reversed by melatonin administration. The analysis of lipid fractions revealed that only the cholesteryl ester fraction was affected by melatonin. Histological studies of the carotid artery intima revealed the appearance, in hypercholesterolemic rats, of fatty streaks produced by a mass of foam cells covered by the endothelium and by a thin layer of mononucleated cells. These changes were prevented by melatonin. We conclude that long-term melatonin administration modifies the fatty acid composition of rat plasma and liver lipids and ameliorates the arterial fatty infiltration induced by cholesterol.

[Dietary intake of n-3 fatty acids and the risk of acute myocardial infarction: a case-control study]

BACKGROUND

There is some dispute about the role of fish and n-3 polyunsaturated fatty acids (n-3 PUFA) consumption on the prevention of coronary heart disease. The aim of this study was to analyze the relationship between n-3 PUFA and fish consumption and the risk of a first acute myocardial infarction (AMI) in a low risk population from Navarre (Spain).

METHOD

A hospital-based case-control study was conducted in Pamplona (Spain). We included 171 patients (81% males, age < 80 years) who were admitted with a first acute myocardial infarction and 171 age, gender and hospital-matched controls were selected. A validated semi-quantitative food frequency questionnaire was administered and face-to-face interviews were performed. Conditional logistic regression modeling was used to take into account potential confounders.

RESULTS

Adjusted odds ratio (OR) and 95% confidence intervals (CI) for the second and third tertile of n-3 PUFA intake were 0.44 (95% CI, 0.21-0.91) and 0.47 (95% CI, 0.22-1.00), respectively. Trend test was not statistically significant. Adjusted OR and 95% CI for the second and third tertile of fish consumption were 0.40 (95% CI, 0.19-0.83) and 0.42 (95% CI, 0.19-0.93), respectively. Additional adjusting for n-3 PUFA led to a non-significant association between fish consumption and AMI.

CONCLUSIONS

This study reveals a protective effect of n-3 PUFA and fish consumption against AMI. Our results suggest that a threshold exists in the quantitative dose-response relationship between fish intake and AMI.

Moderate intake of n-3 fatty acids is associated with stable erythrocyte resistance to oxidative stress in hypertriglyceridemic subjects

BACKGROUND

The important triacylglycerol-lowering capacity of n-3 fatty acids is counterbalanced by their inherent sensitivity to oxidation. Inconsistent results about the latter have been reported in hypertriglyceridemic individuals. After incorporation into cell membranes, n-3 fatty acids may alter membrane-related functions. In view of the distinct composition of hypertriglyceridemic membranes and the prooxidant status in this condition, it can be surmised that cell enrichment with the oxidizable n-3 fatty acids will be associated with an increased hemolytic process.

OBJECTIVE

We sought to evaluate the effect of fish oil consumption on n-3 fatty acid incorporation into erythrocyte membranes and subsequent ex vivo oxidative-stress-induced hemolysis in normotriglyceridemic and hypertriglyceridemic subjects.

DESIGN

Sixteen normotriglyceridemic and 12 hypertriglyceridemic subjects were given 6 g fish oil/d for 8 wk. Blood samples were collected before and 4 and 8 wk after treatment. Resistance to 2,2'-azobis (2-amidinopropane) dihydrochloride (AAPH)-induced hemolysis was assayed in fresh erythrocyte suspensions, and erythrocyte samples were stored at -70 degrees C for later analysis of cholesterol, hemoglobin, fatty acids, vitamin E, and glutathione peroxidase activity.

RESULTS

Fish oil supplementation induced n-3 fatty acid incorporation in normotriglyceridemic and hypertriglyceridemic erythrocyte membranes without decreasing their resistance to AAPH. n-3 Fatty acids significantly protected normotriglyceridemic but not hypertriglyceridemic erythrocytes against hemolysis. In normotriglyceridemic subjects only, the higher resistance to hemolysis correlated with changes in cell vitamin E.

CONCLUSION

Although they exhibit a high susceptibility to oxidation, n-3 fatty acids may preserve membrane integrity and represent an added benefit in the treatment of hypertriglyceridemic patients.

One-year treatment with ethyl esters of n-3 fatty acids in patients with hypertriglyceridemia and glucose intolerance: reduced triglyceridemia, total cholesterol and increased HDL-C without glycemic alterations

n-3 Fatty acids in the form of ethyl esters (EE) allow lower daily doses and improved compliance. Administration of n-3 fatty acids to patients with glucose intolerance has led to controversial findings, some studies indicating worsening of the disorder, others no effect, or an improvement. A total of 935 patients with hypertriglyceridemia, associated with additional cardiovascular risk factors, i.e. glucose intolerance, NIDDM and/or arterial hypertension were entered a double blind (DB) protocol lasting 6 months with n-3 EE versus placebo, followed by a further 6 months of open study (n = 868) on 2 g a day of n-3 EE. At the end of the DB period, triglyceridemia in the total group was reduced significantly more by n-3 EE, without alterations in glycemic parameters. In the 6 months open follow up, patients on n-3 EE with type IIB hyperlipoproteinemia showed a significant reduction of total cholesterol, both in cases with (-4.15% vs. the 6 month levels) and without NIDDM (-3.8%). HDL-cholesterol had an overall mean rise of 7.4%, maximal in type IV patients with (+9.1%) and without (+10.1%) NIDDM. No alterations in glycemic parameters were detected in treated patients. Administration of n-3 EE to patients with hypertriglyceridemia associated with NIDDM or impaired glucose tolerance appears safe and effective.