Fish oil significantly alters fatty acid profiles in various lipid fractions but not atherogenesis in apo E-KO mice

Caprylic acid suppresses inflammation via TLR4/NF-κB signaling and improves atherosclerosis in ApoE-deficient mice

Background

As reported previously by our group, medium-chain triglycerides can ameliorate atherosclerosis. Given that TLR4 is closely related to atherosclerosis, we hypothesized herein that caprylic acid (C8:0) would suppress inflammation via TLR4/NF-κB signaling and further promote the amelioration of atherosclerosis in apoE- deficient (apoE^-/-) mice.

Methods

Fifty 6-week male apoE^-/- mice were randomly allocated into five diet groups: a high-fat diet (HFD) without or with 2% caprylic acid (C8:0), capric acid (C10:0), stearic acid (C18:0), or linolenic acid (C18:3). RAW246.7 cells were treated with caprylic acid (C8:0), docosahexenoic acid (DHA), palmitic acid (C16:0), and lipopolysaccharide (LPS) with or without TLR4 knock-down (TLR4-KD). The serum lipid profiles, inflammatory biomolecules, and mRNA and protein expression levels were measured. Atherosclerotic lesions that occurred in the aorta and aortic sinuses were evaluated and quantified.

Results

Our results indicated that C8:0 reduced body fat, improved the lipid profiles, suppressed inflammatory cytokine production, downregulated aortic TLR4, MyD88, NF-κB, TNF-α, IKKα, and IKKβ mRNA expression, and alleviated atherosclerosis in the apoE^-/- mice (P < 0.05). In RAW 264.7 cells, C8:0 diminished the inflammatory response and both mRNA and protein expression of TLR4, MyD88, NF-κB, and TNF-α compared to those in the LPS and C16:0 groups (P < 0.05). However, in the TLR4-KD RAW 264.7 cells, C8:0 significantly upregulated NF-κB mRNA and protein expression compared to those in the C16:0 and DHA groups.

Conclusions

These results suggest that C8:0 functions via TLR4/NF-κB signaling to improve the outcomes of apoE^-/- mice through suppressing inflammation and ameliorating atherosclerosis. Thus, C8:0 may represent as a promising nutrient against chronic inflammatory diseases.

Addition of aspirin to a fish oil-rich diet decreases inflammation and atherosclerosis in ApoE-null mice

Aspirin (ASA) is known to alter the production of potent inflammatory lipid mediators, but whether it interacts with omega-3 fatty acids (FAs) from fish oil to affect atherosclerosis has not been determined. The goal was to investigate the impact of a fish oil-enriched diet alone and in combination with ASA on the production of lipid mediators and atherosclerosis. ApoE(-/-) female mice were fed for 13weeks one of the four following diets: omega-3 FA deficient (OD), omega-3 FA rich (OR) (1.8g omega-3 FAs/kg·diet per day), omega-3 FA rich plus ASA (ORA) (0.1g ASA/kg·diet per day) or an omega-3 FA deficient plus ASA (ODA) with supplement levels equivalent to human doses. Plasma lipids, atherosclerosis, markers of inflammation, hepatic gene expression and aortic lipid mediators were determined. Hepatic omega-3 FAs were markedly higher in OR (9.9-fold) and ORA (7-fold) groups. Mice in both OR and ORA groups had 40% less plasma cholesterol in very low-density lipoprotein-cholesterol and low-density lipoprotein fractions, but aortic plaque area formation was only significantly lower in the ORA group (5.5%) compared to the OD group (2.5%). Plasma PCSK9 protein levels were approximately 70% lower in the OR and ORA groups. Proinflammatory aortic lipid mediators were 50%-70% lower in the ODA group than in the OD group and more than 50% lower in the ORA group. In summary, less aortic plaque lesions and aortic proinflammatory lipid mediators were observed in mice on the fish oil diet plus ASA vs. just the fish oil diet.

Docosahexaenoic acid supplementation modifies fatty acid incorporation in tissues and prevents hypoxia induced-atherosclerosis progression in apolipoprotein-E deficient mice

The n-3 polyunsaturated fatty acid, docosahexaenoic acid (DHA), displays anti-inflammatory properties that may prevent atherosclerosis progression. Exposure of apolipoprotein-E deficient (ApoE(-/-)) mice to chronic intermittent hypoxia (CIH) accelerates atherosclerosis progression. Our aim was to assess DHA-supplementation influence on fatty acid incorporation in different tissues/organs and on atherosclerosis progression in ApoE(-/-) mice exposed to CIH. ApoE(-/-) mice were exposed to CIH or normoxia (N) and randomized to four groups (N control, CIH control, N+DHA, and CIH+DHA). DHA-supplementation enhanced DHA and reduced arachidonic acid (AA) contents in tissues/organs. CIH control mice exhibited increased atherosclerosis lesion sizes compared to N control mice. DHA prevented CIH induced atherosclerosis but did not improve atherosclerosis burden in N mice. Aortic matrix metalloproteinase-2 (MMP-2) expression was decreased in CIH+DHA mice (p=0.007). DHA-supplementation prevented CIH-induced atherosclerosis acceleration. This was associated with a decrease of AA incorporation and of aortic MMP-2 gene expression.

The effects of fish oil consumption on cardiovascular remodeling in ApoE deficient mice

Owing to their spontaneous development of atherosclerosis, apolipoprotein E knockout mice (ApoE(KO)) are one of the best studied animal models for this disease. Little is known about the utility of various omega-3 fatty acid regimens, in particular fish oils, in preventing cardiac disease in ApoE(KO) mice. The purpose of this study was to determine the cardiovascular effects of omega-3 fatty acid supplementation with either safflower oil (control), fish oil, flaxseed oil, or designed oil in ApoE(KO) mice fed a high-fat diet for a total of 16 weeks. In-vivo cardiac function was assessed weekly using murine echocardiography. Blood pressure, plasma lipid levels, and brain natriuretic peptide (BNP) were serially measured. The results show that ApoE(KO) mice fed fish oil demonstrated an increase in left ventricular wall thickness as a result of increased afterload. Despite chronic treatment with fish oil over 16 weeks, blood pressure increased in ApoE(KO) mice by 20% compared with the baseline. Both echocardiographic evidence of left ventricular hypertrophy and biochemical increase in BNP levels confirmed diastolic dysfunction in ApoE(KO) mice fed fish oil. This suggests that high-fat diet supplemented with fish oil may lead to adverse cardiovascular effects in ApoE deficient mice.

Omega-3 fatty acids ameliorate atherosclerosis by favorably altering monocyte subsets and limiting monocyte recruitment to aortic lesions

OBJECTIVE

Fish oil, containing omega-3 fatty acids, attenuates atherosclerosis. We hypothesized that omega-3 fatty acid-enriched oils are atheroprotective through alteration of monocyte subsets and their trafficking into atherosclerotic lesions.

METHODS AND RESULTS

Low-density lipoprotein receptor knockout and apolipoprotein E(-/-) mice were fed diets containing 10% (calories) palm oil and 0.2% cholesterol, supplemented with an additional 10% palm oil, echium oil (containing 18:4 n-3), or fish oil. Compared with palm oil-fed low-density lipoprotein receptor knockout mice, echium oil and fish oil significantly reduced plasma cholesterol, splenic Ly6C(hi) monocytosis by ≈50%, atherosclerosis by 40% to 70%, monocyte trafficking into the aortic root by ≈50%, and atherosclerotic lesion macrophage content by 30% to 44%. In contrast, atherosclerosis and monocyte trafficking into the artery wall was not altered by omega-3 fatty acids in apolipoprotein E(-/-) mice; however, Ly6C(hi) splenic monocytes positively correlated with aortic root intimal area across all diet groups. In apolipoprotein E(-/-) mice, fish oil reduced the percentage of blood Ly6C(hi) monocytes, despite an average 2-fold higher plasma cholesterol relative to palm oil.

CONCLUSIONS

The presence of splenic Ly6C(hi) monocytes parallels the appearance of atherosclerotic disease in both low-density lipoprotein receptor knockout and apolipoprotein E(-/-) mice. Furthermore, omega-3 fatty acids favorably alter monocyte subsets independently from effects on plasma cholesterol and reduce monocyte recruitment into atherosclerotic lesions.

Enzymatic synthesis of phytosteryl docosahexaneates and evaluation of their anti-atherogenic effects in apo-E deficient mice

Phytosterols have attracted much attention in recent years due to their health benefits, such as cholesterol lowering, anti-inflammatory, anti-atherogenicity, and anti-cancer potential. Docosahexaenoic acid (DHA) has been demonstrated to possess cardioprotective and immune-enhancing effects. Esterification of phytosterols with DHA may render improved physiochemical properties such as solubility, miscibility, oxidative stability and hence bioactivity and bioavailability. Thus, phytosteryl docosahexaneates (PS-DHA) may offer both the benefits of phytosterols and DHA, possibly in a synergistic manner. Here, we describe a method for enzymatic synthesis of phytosteryl docosahexaneates and evaluation of metabolic and cardiovascular benefits in apo-E deficient (apo E-KO) mice. The structures of phytosteryl docosahexaneates were confirmed by infrared (IR) and high performance liquid chromatography-mass spectrometry (HPLC-MS) using both normal and reverse phase chromatography. Apo E-KO mice were fed with an atherogenic diet containing 2% (w/w) PS-DHA for 7 weeks. Plasma lipid levels and the extent and complexity of atherosclerotic lesions were examined and compared with those in the control group. The PS-DHA-treated mice had significantly lower plasma cholesterol levels and three times smaller atherosclerotic lesions in the aortic roots. This pilot study suggests cardiovascular benefits for PS-DHA. Further experimental and clinical studies are needed to confirm such benefits of PS-DHA.

Omega-3 fatty acids and metabolic syndrome: effects and emerging mechanisms of action

Epidemiological, human, animal, and cell culture studies show that n-3 fatty acids, especially α-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), reduce the risk factors of cardiovascular diseases. EPA and DHA, rather than ALA, have been the focus of research on the n-3 fatty acids, probably due to the relatively inefficient conversion of ALA to EPA and DHA in rodents and humans. This review will assess our current understanding of the effects and potential mechanisms of actions of individual n-3 fatty acids on multiple risk factors of metabolic syndrome. Evidence for pharmacological responses and the mechanism of action of each of the n-3 fatty acid trio will be discussed for the major risk factors of metabolic syndrome, especially adiposity, dyslipidemia, insulin resistance and diabetes, hypertension, oxidative stress, and inflammation. Metabolism of n-3 and n-6 fatty acids as well as the interactions of n-3 fatty acids with nutrients, gene expression, and disease states will be addressed to provide a rationale for the use of n-3 fatty acids to reduce the risk factors of metabolic syndrome.

Inhibition of atherosclerotic lesion development in the ApoE-/- mouse by a novel β-oxa polyunsaturated fatty acid

Recent findings that a novel polyunsaturated fatty acid, β-oxa 23:4n-6, inhibits adhesion molecule expression on vascular endothelial cells and leukocyte adhesion led us to examine its ability to inhibit the development of atherosclerosis in the apoE-deficient (apoE) mouse. The mice were kept on normal chow or a high-fat/high-cholesterol diet for various periods and treated with either vehicle or β-oxa 23:4n-6 by the intraperitoneal route. The hearts and aortae were isolated and lesion development at the aortic root was determined. Morphometric assessment revealed that lesion development was a function of compensatory aortic enlargement, suggesting that measurement of plaque size per se is the appropriate assessment of lesion size. Using this criterion, we found that atherosclerosis development was reduced in response to β-oxa 23:4n-6, plaque size by 74% and aortic cross-sectional area by 62%, under an optimized regime. The number of foam cells per unit tissue area in the lesions of β-oxa 23:4n-6-treated mice was significantly reduced by 37.5%. The blood levels of β-oxa23:4n-6 in these mice exceeded the concentrations previously found to inhibit adhesion molecule expression in cultured endothelial cells. These data show that β-oxa23:4n-6 protects against experimental atherosclerosis, most likely by reducing the number of infiltrating monocytes.

Intervention with fish oil, but not with docosahexaenoic acid, results in lower levels of hepatic soluble epoxide hydrolase with time in apoE knockout mice

Long-chain n-3 PUFA from fish oil protect against death from CHD but mechanisms are not well understood. Preliminary results indicate that fish oil may affect the enzyme soluble epoxide hydrolase (sEH) and influence inflammatory pathways in a time-dependent manner. In the present study male apoE knockout (Apoe-/-) mice were randomised to three dietary groups receiving a high-fat high-cholesterol diet supplemented with 2 % (w/w) high-oleic acid sunflower-seed (HOSF) oil, DHA oil or fish oil. Livers and proximal aortas were collected on day 2 and on weeks 1, 2, 4 and 10 to determine hepatic sEH levels, hepatic fatty acid composition, hepatic proteome and atherosclerotic plaque size in the aortic root. Intervention with fish oil, but not with DHA, resulted in significantly lower levels of hepatic sEH levels with time compared with HOSF oil. DHA and fish oil caused differential regulation of thirty-five hepatic proteins which were mainly involved in lipoprotein metabolism and oxidative stress. All mice developed atherosclerosis without differences in plaque size between the three groups. Thus EPA may be responsible for lowering levels of hepatic sEH and both fish oil and DHA could beneficially affect lipoprotein metabolism and oxidative stress.

The hypolipidemic effect of an ethyl ester of algal-docosahexaenoic acid in rats fed a high-fructose diet

Preclinical and clinical studies demonstrate that the omega-3 fatty acids docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) as a triacylglycerol (TAG) or an ethyl ester are protective against cardiovascular disease. Both have significant TAG-lowering effects. We developed a concentrated ethyl ester of DHA (MATK-90, 900 mg/g) using microalgae as its source. This study evaluated the effects that different doses of MATK-90 had on lipid levels and clinical parameters in male Wistar rats fed a high-fructose diet used to induce hypertriglyceridemia (TAG > or = 300 mg/dL). Effects of MATK-90 were compared to those produced by a pharmaceutical product (Lovaza, formerly Omacor, P-OM3; 465 mg EPA + 375 mg DHA), a TAG oil used in food (DHASCO, algal-DHA, 40% DHA by weight), and a control (corn oil). Doses of MATK-90 (0.6, 1.3, 2.5, 5.0 g kg(-1) day(-1)), algal-DHA (2 g DHA kg(-1) day(-1)), and P-OM3 (5.0 g kg(-1) day(-1)) were administered by oral gavage for 28 days. A significant dose-related decrease was observed in TAG and cholesterol levels in all but the lowest dose of MATK-90 treatment group vs. control. The high-dose group of MATK-90 and the P-OM3 group produced similar reductions in TAG levels.

Long-chain n-3 polyunsaturated fatty acids: new insights into mechanisms relating to inflammation and coronary heart disease

Evidence from observational studies, prospective cohort studies and randomized clinical intervention studies indicate that moderate doses of long-chain n-3 polyunsaturated fatty acids (LC n-3 PUFA) significantly decrease risk of fatal coronary heart disease (CHD). Higher doses and longer duration of intervention may also protect from non-fatal CHD events. The exact mechanisms through which LC n-3 PUFA has an effect on CHD are not well established but may include a decrease in fasting and postprandial triacylglycerol levels, a decrease in arrhythmias, modulation of platelet aggregation and decreased synthesis of pro-inflammatory agents. The mechanistic relation between LC n-3 PUFA and inflammation has attracted great interest, and in vitro studies have revealed that these fatty acids decrease endothelial activation, affect eicosanoid metabolism (including epoxygenation pathways) and induce inflammatory resolution. However, the effects of LC n-3 PUFA on established biomarkers of inflammation and endothelial activation in vivo are not strong. Consequently we need new and more sensitive and systemic biomarkers to reveal the effects of LC n-3 PUFA on localized inflammatory processes.

Low n-6:n-3 fatty acid ratio, with fish- or flaxseed oil, in a high fat diet improves plasma lipids and beneficially alters tissue fatty acid composition in mice

BACKGROUND

Health benefits from low n-6:n-3 fatty acid (FA) ratio on cardiovascular risk have been shown. However, the impact of the source of n-3 FAs has not been fully investigated.

AIM

Our purpose was to investigate cardiovascular benefits of oils with a low ratio of n-6:n-3 FAs, but different sources of n-3 FAs in C57BL/6 mice.

METHODS

Twenty-one mice were divided into 3 groups (n=7) and fed a diet supplemented with either a fish or flaxseed oil-based 'designer oils' with an approximate n-6:n-3 FA ratio of 2/1 or with a safflower-oil-based diet with a ratio of 25/1, for 16 weeks. Plasma lipids and fatty acid profile of the liver tissue were characterized.

RESULTS

Compared to baseline, plasma triacylglycerol levels declined (>50%) in all groups by week 4. Plasma cholesterol levels were reduced in both fish and flax groups by 27% and 36%, respectively, as compared to controls at endpoint. The levels of EPA and DHA in liver phospholipids were significantly increased in both fish and flax groups as compared to the control group, with more profound increases in the fish group. Arachidonic acid levels were similarly decreased in the liver tissues from both fish and flax groups as compared to controls.

CONCLUSIONS

Our data suggest that health benefits may be achieved by lowering dietary n-6:n-3 FA even in a high fat diet medium.

A comparison of the effects of fish oil and flaxseed oil on cardiac allograft chronic rejection in rats

Both fish and flaxseed oils are major sources of different n-3 fatty acids. Beneficial effects of fish oil on posttransplantation complications have been reported. The current study aimed to compare the effects of flaxseed and fish oils in a rat cardiac allograft model. Male Fischer and Lewis rats were used as donors and recipients, respectively, to generate a heterotopic cardiac allograft model. Animals were randomly assigned into three groups and fed a diet supplemented with 1) 5% (wt/wt) safflower oil (control, n = 7), 2) 5% (wt/wt) flaxseed oil ( n = 8), or 3) 2% (wt/wt) fish oil ( n = 7), and an intraperitoneal injection of cyclosporine A (CsA; 1.5 mg·kg−1·day−1) over 12 wk. Body weight, blood pressure, plasma levels of lipids, CsA, select cytokines, as well as graft function and chronic rejection features were assessed. Body weight and blood CsA levels were similar among the groups. Relative to controls, both treated groups had lower systolic and diastolic blood pressure and plasma levels of macrophage chemotactic protein-1. Treatment with fish oil significantly ( P < 0.05) lowered plasma levels of triglycerides, total cholesterol, and LDL-cholesterol. HDL-cholesterol concentrations were significantly higher ( P < 0.05) in the flaxseed oil-treated group compared with the other two groups. Both flaxseed oil and fish oil may provide similar biochemical, hemodynamic, and inflammatory benefits after heart transplantation; however, neither of the oils was able to statistically significantly impact chronic rejection or histological evidence of apparent cyclosporine-induced nephrotoxicity in this model.