Excessive dietary linoleic acid induces proinflammatory markers in rats.

Following the historical dietary recommendations, the substitution of polyunsaturated fatty acids (PUFAs) for saturated fatty acids (SFAs) resulted in a dramatic increase of linoleic acid (LA) in the Western diet. While proatherogenic properties of SFAs have been described, the involvement of LA on the inflammatory process remains controversial. Herein, we evaluated the effects of an excessive LA intake on the cytokine-induced expression of endothelial adhesion molecules vascular cell adhesion molecule-1 (VCAM-1) and intercellular cell adhesion molecule-1 (ICAM-1), through the nuclear factor (NF)-κB pathway, in comparison with a control diet and regarding a "positive" SFA diet. Wistar rats were fed experimental diets - a control diet or diets enriched with LA or SFA - for 11 weeks. Plasma lipid parameters and proinflammatory cytokine production such as interleukin-1ß and tumor necrosis factor (TNF)-α were analyzed. Expression of endothelial adhesion molecules and NF-κB was determined by immunohistochemical analysis. No difference was observed in body weight. The enriched diets did not affect triglyceride and total cholesterol levels in plasma. Our results demonstrated that excessive dietary LA intake increased TNF-α levels (P<.05) in plasma. Rats fed the LA-enriched diet showed a significantly higher expression of VCAM-1, ICAM-1 and NF-κB in aortas. In addition, our results demonstrated that an excess of LA is more efficient to activate endothelial molecular process than an excess of SFA. The present study provides further support for the proinflammatory properties of LA and suggests an LA-derivatives pathway involved in the inflammatory process.

Dietary linoleic acid requirements in the presence of α-linolenic acid are lower than the historical 2 % of energy intake value, study in rats.

Previous studies on rats and human subjects have established that the linoleic acid (LA) requirement is 2 % of the total energy intake (en%), but is obtained in the absence of α-linolenic acid (ALA) and consequently appear to be overestimated. This raises questions since a recent study including ALA has suggested to divide the historical value by four. However, this recent study has remained inconclusive because the animals used were not totally LA-deficient animals. For the first time, the present study was especially designed using physiological and biochemical markers and performed in two steps: (1) to achieve a specific n-6 fatty acid deficiency model using growing male rats fed either a 0 en% from LA/0 en% from ALA (0LA/0ALA), 0LA/0·5ALA or 2LA/0·5ALA diet, born from female rats fed a 0LA/0·5ALA diet; and (2) to refine the required level of LA in the presence of ALA using rats fed either a 0LA/0ALA, 0·5LA/0·5ALA, 1LA/0·5ALA, 1·5LA/0·5ALA diet, born from female rats fed a 0LA/0·5ALA diet. The first step shows that the best LA deficiency model was obtained using rats fed the 0LA/0ALA diet, born from female rats fed the 0LA/0·5ALA diet. The second step demonstrates that in growing rats, LA deficiency was corrected with an intake of 1-1·5 en% from LA and 0·5 en% from ALA. These data suggest that the requirements in humans should be revisited, considering the presence of ALA to set up the recommendation for LA.

Influence of the cis-9, cis-12 and cis-15 double bond position in octadecenoic acid (18:1) isomers on the rat FADS2-catalyzed Δ6-desaturation.

Oleic (cis9-18:1), linoleic (cis9,cis12-18:2) and α-linolenic (cis9,cis12,cis15-18:3) acids are well described substrates of the Δ6-desaturase encoded by the mammalian fatty acid desaturase 2 (FADS2) gene. In addition, at least 9 other very structurally different fatty acids have been shown to be Δ6- or even Δ8-desaturated by the FADS2 protein. A better characterization of the substrate specificity of this enzyme is therefore needed. By using commercial cis9-18:1 and chemically synthesized cis12- and cis15-18:1 (sharing the n-6 double bond with 18:2 n-6 and the n-3 double bond with 18:3 n-3, respectively), we tried to decrypt the fatty acid structure driving the FADS2 substrate affinity. We first showed that both recombinant and native rat FADS2 were able to Δ6-desaturate not only the cis9- but also the cis12- and cis15-18:1 isomers. Next, the inhibitory effect of increasing concentrations of each 18:1 isomer was investigated in vitro on the Δ6-desaturation of α-linolenic acid. At equimolar inhibitor/substrate ratio (60 µM), the cis9-18:1 exhibited a significantly higher inhibition (25%) than the cis12- (8%) and cis15-18:1 (5%). This study shows that a single cis double bond in 12- or 15-position in 18:1 is enough to make them low Δ6-desaturable substrates. If a preexisting cis9-double bond is not absolutely required for the Δ6-desaturation of octadecenoic acids, its presence is however crucial to explain the higher enzyme affinity. Compared with oleic acid, the additional presence of a cis12-double bond in linoleic acid increased its inhibitory effect on the Δ6-desaturation of α-linolenic acid at low concentration (30 µM) but not at higher concentrations (60 and 120 µM). In this classification of the decreasing impact of the double bond when it comes closer to the methyl end of octadecenoic acids, the cis11-18:1 (cis-vaccenic acid) should be considered apart since it is itself not Δ6-desaturated but still a good competitive inhibitor of the α-linolenic acid Δ6-desaturation.

Elevated plasma PCSK9 level is equally detrimental for patients with nonfamilial hypercholesterolemia and heterozygous familial hypercholesterolemia, irrespective of low-density lipoprotein receptor defects.

OBJECTIVES: Do elevated proprotein convertase subtilisin/kexin type 9 (PCSK9) levels constitute an even greater risk for patients who already have reduced low-density lipoprotein receptor (LDLR) levels, such as those with heterozygous familial hypercholesterolemia (HeFH)? BACKGROUND: As a circulating inhibitor of LDLR, PCSK9 is an attractive target for lowering LDL-cholesterol (LDL-C) levels. METHODS: Circulating PCSK9 levels were measured by enzyme-linked immunosorbent assay in nontreated patients with HeFH carrying a D206E (n = 237), V408M (n = 117), or D154N (n = 38) LDLR missense mutation and in normolipidemic controls (n = 152). Skin fibroblasts and lymphocytes were isolated from a subset of patients and grown in 0.5% serum and mevastatin with increasing amounts of recombinant PCSK9. LDLR abundance at the cell surface was determined by flow cytometry. RESULTS: PCSK9 reduced LDLR expression in a dose-dependent manner in control and FH fibroblasts to similar extents, by up to 77 ± 8% and 82 ± 7%, respectively. Likewise, PCSK9 reduced LDLR abundance by 39 ± 8% in nonfamilial hypercholesterolemia (non-FH) and by 45 ± 10% in HeFH lymphocytes, irrespective of their LDLR mutation status. We found positive correlations of the same magnitude between PCSK9 and LDL-C levels in controls (beta = 0.22; p = 0.0003), D206E (beta = 0.20; p = 0.0002), V408M (beta = 0.24; p = 0.0002), and D154N (beta = 0.25; p = 0.048) patients with HeFH. The strengths of these associations were all similar. CONCLUSIONS: Elevated PCSK9 levels are equally detrimental for patients with HeFH or non-FH: a 100-ng/ml increase in PCSK9 will lead to an increase in LDL-C of 0.20 to 0.25 mmol/l in controls and HeFH alike, irrespective of their LDLR mutation. This explains why patients with non-FH or HeFH respond equally well to monoclonal antibodies targeting PCSK9.

Linoleic acid: between doubts and certainties.

Linoleic acid is the most abundant polyunsaturated fatty acid in human nutrition and represents about 14 g per day in the US diet. Following the discovery of its essential functions in animals and humans in the early 1920's, studies are currently questioning the real requirement of linoleic acid. It seems now overestimated and creates controversy: how much linoleic acid should be consumed in a healthy diet? Beyond the necessity to redefine the dietary requirement of linoleic acid, many questions concerning the consequences of its excessive consumption on human health arise. Linoleic acid is a direct precursor of the bioactive oxidized linoleic acid metabolites. It is also a precursor of arachidonic acid, which produces pro-inflammatory eicosanoids and endocannabinoids. A majority of the studies on linoleic acid and its derivatives show a direct/indirect link with inflammation and metabolic diseases. Many authors claim that a high linoleic acid intake may promote inflammation in humans. This review tries to (i) highlight the importance of reconsidering the actual requirement of linoleic acid (ii) point out the lack of knowledge between dietary levels of linoleic acid and the molecular mechanisms explaining its physiological roles (iii) demonstrate the relevance of carrying out further human studies on the single variable linoleic acid.

The PCSK9 decade.

PCSK9 proprotein convertase subtilisin/kexin type (PCSK9) is a crucial protein in LDL cholesterol (LDL-C) metabolism by virtue of its pivotal role in the degradation of the LDL receptor. In recent years, both in vitro and in vivo studies have greatly supplemented our understanding of the (patho)physiological role of PCSK9 in human biology. In the current review, we summarize studies published or in print before May 2012 concerning the physiological role of PCSK9 in cholesterol metabolism. Moreover, we briefly describe the clinical phenotypes encountered in carriers of mutations in the gene encoding PCSK9. As PCSK9 has emerged as a novel target for LDL-C lowering therapy, methods to inhibit PCSK9 will also be reviewed. Initial data from investigations of PCSK9 inhibition in humans are promising and indicate that PCSK9 inhibition may be a viable new therapeutic option for the treatment of dyslipidemia and associated cardiovascular diseases.