Effects of Linoleic and Alpha-Linolenic Ratios and Concentrations on In Vitro Endothelial Cell Responses

Impact of dietary n-6/n-3 fatty acid ratio of atherosclerosis risk: A review

Atherosclerosis is a causative factor associated with cardiovascular disease (CVD). Over the past few decades, extensive research has been carried out on the relationship between the n-6/n-3 fatty acid ratio of ingested lipids and the progression of atherosclerosis. However, there are still many uncertainties regarding the precise nature of this relationship, which has led to challenges in providing sound dietary advice to the general public. There is therefore a pressing need to review our current understanding of the relationship between the dietary n-6/n-3 fatty acid ratio and atherosclerosis, and to summarize the underlying factors contributing to the current uncertainties. Initially, this article reviews the association between the n-6/n-3 fatty acid ratio and CVDs in different countries. A summary of the current understanding of the molecular mechanisms of n-6/n-3 fatty acid ratio on atherosclerosis is then given, including inflammatory responses, lipid metabolism, low-density lipoprotein cholesterol oxidation, and vascular function. Possible reasons behind the current controversies on the relationship between the n-6/n-3 fatty acid ratio and atherosclerosis are then provided, including the precise molecular structures of the fatty acids, diet-gene interactions, the role of fat-soluble phytochemicals, and the impact of other nutritional factors. An important objective of this article is to highlight areas where further research is needed to clarify the role of n-6/n-3 fatty acid ratio on atherosclerosis.

MyD88 determines the protective effects of fish oil and perilla oil against metabolic disorders and inflammation in adipose tissue from mice fed a high-fat diet

BACKGROUND

The beneficial effects of ω-3 polyunsaturated fatty acids (PUFA) vary between different sources. However, there is a paucity of comparative studies regarding the effects and mechanisms of marine and plant ω-3 PUFA on obesity.

OBJECTIVE

The aim of this study was to evaluate the effects of fish oil (FO) and perilla oil (PO) on glucolipid metabolism, inflammation, and adipokine in mice fed a high-fat (HF) diet in association with the contribution of toll-like receptor 4 (TLR4)/myeloid differentiation primary response 88 (MyD88) pathway.

METHODS

C57BL/6J mice and MyD88-/- mice were randomly divided into 4 groups: normal chow diet, HF diet, HF diet accompanied by daily gavage with either FO or PO. After 4 weeks, blood biochemistries, adipocyte histology, mRNA, and protein expression of MyD88-dependent and -independent pathways of TLR4 signaling in epididymal adipose tissue were measured.

RESULTS

In C57BL/6J mice, there were no statistical differences between FO and PO in decreasing body weight, glucose, insulin, triglyceride, total cholesterol, interleukin-6, and increasing adipocyte counts. FO and PO decreased mRNA and protein expression of TLR4, MyD88, tumor necrosis factor receptor-associated factor 6, inhibitor of nuclear factor kappa B kinase beta and nuclear factor-kappa B p65. In MyD88-/- mice, the beneficial effects of FO and PO on HF diet-induced metabolism abnormalities and inflammation were abolished. FO and PO had no impacts on mRNA and protein expression of receptor-interacting protein-1, interferon regulate factor 3, and nuclear factor-kappa B p65.

CONCLUSION

FO and PO exhibit similar protective effects on metabolic disorders and inflammation through inhibiting TLR4 signaling in a manner dependent on MyD88. These findings highlight plant ω-3 PUFA as an attractive alternative source of marine ω-3 PUFA and reveal a mechanistic insight for preventive benefits of ω-3 PUFA in obesity and related metabolic diseases.

Atherosclerosis Development and Aortic Contractility in Hypercholesterolemic Rabbits Supplemented with Two Different Flaxseed Varieties

Alpha-linolenic acid (ALA) is widely regarded as the main beneficial component of flax for the prevention of cardiovascular disease. We evaluated the effect of the transgenic flaxseed W86-which is rich in ALA-on the lipid profile, atherosclerosis progression, and vascular reactivity in hypercholesterolemic rabbits compared to the parental cultivar Linola with a very low ALA content. Rabbits were fed a basal diet (control) or a basal diet supplemented with 1% cholesterol, 1% cholesterol and 10% flaxseed W86, or 1% cholesterol and 10% Linola flaxseed. A high-cholesterol diet resulted in an elevated plasma cholesterol and triglyceride levels compared to the control animals. Aortic sections from rabbits fed Linola had lower deposits of foamy cells than those from rabbits fed W86. A potassium-induced and phenylephrine-induced contractile response was enhanced by a high-cholesterol diet and not influenced by the W86 or Linola flaxseed. Pretreatment of the aortic rings with nitro-L-arginine methyl ester resulted in a concentration-dependent tendency to increase the reaction amplitude in the control and high-cholesterol diet groups but not the flaxseed groups. Linola flaxseed with a low ALA content more effectively reduced the atherosclerosis progression compared with the W86 flaxseed with a high concentration of stable ALA. Aorta contractility studies suggested that flaxseed ameliorated an increased contractility in hypercholesterolemia but had little or no impact on NO synthesis in the vascular wall.

Beneficial effect of walnuts on vascular tone is associated with Akt signalling, voltage-dependent calcium channel LTCC and ATP-sensitive potassium channel Kv1.2

Consumption of walnuts is beneficial for cardiovascular health. To study walnut effects on proteins involved in vascular tone regulation, control and fructose-fed rats were subjected to walnut diet for 6 weeks. In contrast with increased energy intake and body mass gain, aortic protein level of L-type calcium channel alpha subunit was decreased and the level of SUR2B subunit of ATP-sensitive K + channel was increased in healthy rats subjected to walnuts, together with improved Akt phosphorylation. Upon the walnut diet in rats subjected to fructose overload, the rise in energy intake and body mass gain, was followed by an increase in blood insulin. Although SUR2B level was elevated, the level of sodium-calcium exchanger NCX1 and inducible nitric oxide synthase were reduced and increased, respectively. In summary, walnut consumption was accompanied with moderate beneficial vascular effect in healthy rats, while an effect of walnut in rats with metabolic disturbances was rather controversial.

Lowering the linoleic acid to alpha-linoleic acid ratio decreases the production of inflammatory mediators by cultured human endothelial cells

Alpha-linolenic acid (ALA) and linoleic acid (LA) are precursors for longer-chain more unsaturated fatty acids and for lipid signalling molecules that may influence inflammatory processes through a variety of mechanisms. The actions of LA and ALA may be divergent and interdependent. The aim of this study was to investigate the incorporation and metabolism of ALA and LA in cultured in EA.hy926 endothelial cells and the production of inflammatory mediators (VEGF, RANTES, ICAM-1, MCP-1, IL-6 and IL-8) by these cells when exposed to different concentrations of ALA, LA and ratios of LA:ALA. Human endothelial cells were cultured with either culture medium or culture medium supplemented with ALA, LA or various ratios of LA:ALA (1:4, 1:1, 4:1, 9:1 or 19:1) followed by 24 h TNF-α stimulation; the total concentration of ALA plus LA was kept constant at 100 μM. The incorporation and metabolism of ALA and LA was measured using gas chromatography. The production of inflammatory mediators in the supernatant was assessed using a Luminex Multi-Analyte kit. Both ALA and LA were incorporated and metabolised by the endothelial cells. Cells incubated with ALA had a statistically significantly lower production of VEGF, RANTES, ICAM-1, MCP-1 and IL-6 compared to cells incubated without additional ALA. LA was not found to exert pro-inflammatory effects. Cells incubated with low LA:ALA ratios had lower production of VEGF, RANTES, MCP-1 and IL-6 when compared with a LA:ALA ratio of 19:1. These findings suggest that a low LA:ALA ratio exerts anti-inflammatory effects by lowering the production VEGF, RANTES, ICAM-1, MCP-1 and IL-6 in TNF-α stimulated endothelial cells compared to a high ratio. These effects were likely mediated by ALA, but LA may also possess some anti-inflammatory effects.