Conjugated Linoleic Acid and Alpha Linolenic Acid Improve Cholesterol Homeostasis in Obesity by Modulating Distinct Hepatic Protein Pathways

Abstract

Scope: High-fat diet (HFD)-induced obesity impairs macrophage-to-feces reverse cholesterol transport (RCT). It is hypothesized that dietary supplementation with the polyunsaturated fatty acids conjugated linoleic acid (CLA) or alpha linolenic acid (ALA) would prevent HFD-impaired RCT by modulating hepatic protein pathways. Methods and results: ApoE3L.CETP mice are fed a HFD supplemented ± CLA or ALA for 12 weeks and in vivo macrophage-to-feces RCT is determined. Hepatic cholesterol transporters and the hepatic proteome are assessed by immunoblotting and mass spectrometry, respectively. Mice fed HFD alone, but not ALA-HFD or CLA-HFD, exhibit increased systemic cholesterol levels, increased 3 H-cholesterol levels in plasma and liver but not feces during RCT, and reduced hepatic ABCG5/8 expression relative to LFD. ALA-HFD significantly reduces liver weight, hepatic cholesterol levels, and expression of the cholesterol synthesis enzyme farnesyl pyrophosphate synthase relative to HFD. ALA further increases the expression of acetyl-coA oxidase-associated proteins and suppress PPAR -induced proteins relative to HFD. CLA does not significantly attenuate hepatic lipid levels but is associated with reduced hepatic expression of fatty acid binding protein (FABP)-1/FABP4 levels relative to HFD, and reduced inflammatory pathway activation relative to ALA-HFD.

Co‐option of PPARα in the regulation of lipogenesis and fatty acid oxidation in CLA‐induced hepatic steatosis

“…For in vivo studies, the CLA used was a commercially available mixture of equal amounts of c9t11 and t10c12 (1:1; den Hartigh, 2019; Koba & Yanagita, 2014). Indeed, most in vivo studies have used mixtures of CLA for dietary lipid supplementation (O'Reilly et al, 2020; Tsuboyama‐Kasaoka et al, 2000; Y. Wang & Jones, 2004) because it is more closely related to the application in human health. For in vitro mechanistic studies, purified CLA was mixed with 100% ethanol, dried in a nitrogen atmosphere, and then dissolved in 0.1 M NaOH for a fatty acid‐NaOH stock solution of 100 mM.…”

“…For in vivo studies, the CLA used was a commercially available mixture of equal amounts of c9t11 and t10c12 (1:1; den Hartigh, 2019; Koba & Yanagita, 2014). Indeed, most in vivo studies have used mixtures of CLA for dietary lipid supplementation (O'Reilly et al, 2020;Tsuboyama-Kasaoka et al, 2000;Y. Wang & Jones, 2004) because it is more closely related to the application in human health.…”

Impact of Dietary Lipids on the Reverse Cholesterol Transport: What We Learned from Animal Studies

“…In contrast with the critical role of cholesterol on the entire RCT pathway [ 28 ], the effect of PUFA supplementation on m-RCT did not differ from that observed when saturated fatty acids were added to the high-fat, high-cholesterol diet [ 180 ]. Although this lack of effect contrasts with the stimulating effects of ω-3 PUFA C20:5 EPA and C22:6 DHA on the rate of fecal macrophage-derived cholesterol excretion [ 30 , 161 ], these results would be consistent with the absence of effects when comparing low- and high-soybean oil-enriched diets (which are rich in n-6 PUFA) in mice [ 30 ] or when evaluating the impact of alpha linoleic acid supplementation (representing 0.7% of calories from fats) in a high-fat diet in CETP-expressing apoE3 Leiden mice [ 165 ]. Importantly, this PUFA did not induce a further increase in the expression of ABCG5 and G8 in mice [ 30 , 180 ], rather suggesting differences in the bioactivity of PUFA species among different supplemented diets.…”

“…The impact of rumenic acid on m-RCT is more controversial. In the study mentioned above on humanized apoE3Leiden-CETP-expressing mice fed with a high-fat diet supplemented with CLA (representing 0.7% of calories from fats), cholesterol mobilization from macrophages to the plasma, liver, and feces was not improved compared with control animals [ 165 ]. Conversely, the presence of 4% w/w of total fatty acids of rumenic acid in milk administered to hamsters caused an increase in HDL levels and the upregulation of ABCA1 expression [ 166 ].…”

A Soap‐Free Strategy for One‐Pot Synthesizing Conjugated Linoleic Acid: Alkali Isomerization of Linoleic Acid through Preferential Esterification Pathway

“…The most predominant biologically active isomers in natural CLA are "c9, t11" CLA, and "t10, c12" CLA (Giordano et al, 2011). Previous studies have shown that natural CLA has the potential to reduce body fat (Sandri et al, 2020) and cholesterol (O'Reilly et al, 2020;Yeonhwa Park et al, 2010), and enhances immunity (Park et al, 2008). In addition to being the essential fatty acid for human, CLA is also the material for synthesizing some structured lipids (Zou et al, 2020).…”