trans-Vaccenic acid

Fatty Acid Desaturase 3 (FADS3) Is a Specific ?13-Desaturase of Ruminant trans-Vaccenic Acid

In mammalian species, the Fatty Acid Desaturase (FADS) gene cluster includes FADS1 (?5-desaturase), FADS2 (?6-desaturase), and a third gene member, named FADS3. According to its high degree of nucleotide sequence homology with both FADS1and FADS2, FADS3 was promptly suspected by researchers in the field to code for a new mammalian membrane-bound fatty acid desaturase. However, no catalytic activity was attributed to the FADS3 protein for a decade, until the rat FADS3 protein was shown in vitro to be able to catalyze the unexpected ?13-desaturation of trans-vaccenic acid, producing the trans11,cis13-conjugated linoleic acid isomer. This review summarizes the recent investigations establishing the FADS3 enzyme as a reliable mammalian trans-vaccenate ?13-desaturase in vivo and tries to identify further unresolved issues that need to be addressed.

Effect of lipid supplementation on the endogenous synthesis of milk cis-9,trans-11 conjugated linoleic acid in dairy sheep and goats: A tracer assay with 13C-vaccenic acid

A major proportion of milk rumenic acid (RA; cis-9,trans-11 CLA) is synthesized through mammary Δ⁹-desaturation of vaccenic acid (VA; trans-11 18:1). Diet composition may determine the relative contribution of this endogenous synthesis to milk RA content, with effects that might differ between ruminant species. However, this hypothesis is mostly based on estimated values, proxies of stearoyl-CoA desaturase (SCD) activity, and indirect comparisons between publications in the literature. With the aim of providing new insights into this issue, in vivo Δ⁹-desaturation of ¹³C-labeled VA (measured via milk ¹³C-VA and -RA secretion) was directly compared in sheep and goats fed a diet without lipid supplementation or including 2% of linseed oil. Four Assaf sheep and 4 Murciano-Granadina goats were used in a replicated 2 × 2 crossover design to test the effects of the 2 dietary treatments during 2 consecutive 25-d periods. On d 22 of each period, 500 mg of ¹³C-VA were i.v. injected to each animal. Dairy performance, milk fatty acid profile, including isotope analysis, and mammary mRNA abundance of genes coding for SCD were examined on d 21 to 25 of each period. Supplementation with linseed oil improved milk fat concentration and increased the content of milk VA and RA. However, the isotopic tracer assay suggested no variation in the relative proportion of VA desaturated to milk RA, and the percentage of this CLA isomer deriving from SCD activity would remain constant regardless of dietary treatment. These results put into question a major effect of lipid supplementation on the endogenous synthesis of milk RA and support that mammary Δ⁹-desaturation capacity would not represent a limiting factor when designing feeding strategies to increase milk RA content. The lack of diet-induced effects was common to caprines and ovines, but inherent interspecies differences in mammary lipogenesis were found. Thus, the higher proportions of VA desaturation and endogenous synthesis of milk RA in sheep supported a greater SCD activity compared with goats, a finding that was not associated with the similar mRNA abundance of SCD1 in the 2 species. On the other hand, transfer efficiency of the isotopic tracer to milk was 37% higher in caprine than in ovine, suggesting a greater efficiency in mammary fatty acid uptake from plasma in caprine.

Isomerization of vaccenic acid to cis and trans C18:1 isomers during biohydrogenation by rumen microbes

In ruminants, cis and trans C18:1 isomers are intermediates of fatty acid transformations in the rumen and their relative amounts shape the nutritional quality of ruminant products. However, their exact synthetic pathways are unclear and their proportions change with the forage:concentrate ratio in ruminant diets. This study traced the metabolism of vaccenic acid, the main trans C18:1 isomer found in the rumen, through the incubation of labeled vaccenic acid with mixed ruminal microbes adapted to different diets. [1-(13)C]trans-11 C18:1 was added to in vitro cultures with ruminal fluids of sheep fed either a forage or a concentrate diet. (13)C enrichment in fatty acids was analyzed by gas-chromatography-mass spectrometry after 0, 5 and 24 h of incubation. (13)C enrichment was found in stearic acid and in all cis and trans C18:1 isomers. Amounts of (13)C found in fatty acids showed that 95% of vaccenic acid was saturated to stearic acid after 5 h of incubation with the concentrate diet, against 78% with the forage diet. We conclude that most vaccenic acid is saturated to stearic acid, but some is isomerized to all cis and trans C18:1 isomers, with probably more isomerization in sheep fed a forage diet.

Retroconversion of dietary trans-vaccenic (trans-C18:1 n-7) acid to trans-palmitoleic acid (trans-C16:1 n-7): proof of concept and quantification in both cultured rat hepatocytes and pregnant rats

Trans-palmitoleic acid (trans-C16:1 n-7 or trans-Δ9-C16:1, TPA) is believed to improve several metabolic parameters according to epidemiological data. TPA may mainly come from direct intakes: however, data are inconsistent due to its very low amount in foods. Instead, TPA might arise from dietary trans-vaccenic acid (trans-C18:1 n-7, TVA), which is more abundant in foods. TVA chain-shortening would be involved, but formal proof of concept is still lacking to our knowledge. Therefore, the present study aimed at providing in vitro and in vivo evidence of TVA retroconversion to TPA. First, fresh rat hepatocytes cultured with growing doses of TVA were able to synthesize growing amounts of TPA, according to a 10% conversion rate. In addition, TPA was found in secreted triacylglycerols (TAG). Inhibiting peroxisomal β-oxidation significantly reduced TPA synthesis, whereas no effect was observed when mitochondrial β-oxidation was blocked. Second, pregnant female rats fed a TVA-supplemented diet free of TPA did metabolize dietary TVA, leading to detectable amounts of TPA in the liver. Apart from the brain, TPA was also found in all analyzed tissues, including the mammary gland. Hepatic peroxisomal β-oxidation of dietary TVA, combined with exportation of TPA under VLDL-TAG, may explain amounts of TPA in other tissues. In conclusion, dietary TVA undergoes peroxisomal β-oxidation and yields TPA. Thus, not only TPA circulating levels in humans can be explained by dietary TPA itself, but dietary TVA is also of importance.

Trans-vaccenic acid inhibits proliferation and induces apoptosis of human nasopharyngeal carcinoma cells via a mitochondrial-mediated apoptosis pathway

Background: Intake of trans fatty acids (TFAs) from partially hydrogenated vegetable oil is associated with a variety of adverse outcomes, but little is known about the health effects of ruminant trans fats. Trans-vaccenic acid (TVA) is a naturally occurring TFA found in the fat of ruminants and in human dairy products. The present study was conducted to investigate the anticancer activity and underlying mechanisms of TVA on human nasopharyngeal carcinoma (NPC) 5-8F and CNE-2 cells.
Methods: A CCK8 assay was used to determine the effect of TVA and the Mcl-1 inhibitor S63845 on the proliferation of NPC cells. Apoptosis was measured using flow cytometry. Western blotting was used to detect the protein expression levels of factors associated with Bcl-2-family protein signaling and Akt signaling.
Results: TVA significantly inhibited cell proliferation in a dose-dependent manner. Mechanistic investigation demonstrated that TVA significantly decreased p-Akt levels and Bad phosphorylation on Ser-136 and Ser-112. More importantly, we discovered that the Mcl-1 inhibitor S63845 synergistically sensitized NPC cells to apoptosis induction by TVA.
Conclusion: TVA can inhibit NPC cell growth and induced apoptosis through the inhibition of Bad/Akt phosphorylation. The combined use of TVA and Mcl-1 inhibitors offers a potential advantage for nasopharyngeal cancer treatment.