The identification of QTL that affect the fatty acid composition of milk on sheep chromosome 11

In this work, we analysed 11 genetic markers localized on OAR11 in a commercial population of Spanish Churra sheep to detect QTL that underlie milk fatty acid (FA) composition traits. Following a daughter design, we analysed 799 ewes distributed in 15 half‐sib families. Eight microsatellite markers and three novel SNPs identified in two genes related to fatty acid metabolism, acetyl‐CoA carboxylase α (ACACA) and fatty acid synthase (FASN), were genotyped in the whole population under study. The phenotypic traits considered in the study included 22 measurements related to the FA composition of the milk and three other milk production traits (milk protein percentage, milk fat percentage and milk yield). Across‐family regression analysis revealed four significant QTL at the 5% chromosome‐wise level influencing contents of capric acid (C10:0), lauric acid (C12:0), linoleic conjugated acid (CLA) and polyunsaturated fatty acids (PUFA) respectively. The peaks of the QTL affecting C10:0 and PUFA contents in milk map close to the FASN gene, which has been evaluated as a putative positional candidate for these QTL. The QTL influencing C12:0 content reaches its maximum significance at 58 cM, close to the gene coding for the glucose‐dependent insulinotropic polypeptide. We were not able to find any candidate genes related to fat metabolism at the QTL influencing CLA content, which is located at the proximal end of the chromosome. Further research efforts will be needed to confirm and refine the QTL locations reported here.     

Conjugated linoleic acid-induced fat loss dependence on Delta6-desaturase or cyclooxygenase

Objective: To determine whether conjugated linoleic acid (CLA)–induced body fat loss is dependent upon metabolism of CLA by Δ6‐desaturase, cyclooxygenase, or lipoxygenase. Methods and Procedures: Mice were fed diets with or without CLA and inhibitors to either Δ6‐desaturase (SC‐26196), cyclooxygenase (aspirin), or lipoxygenase (nordihydroguaiaretic acid (NDGA)) for 2 weeks. Body fat percent, lean mass, fat pad weights, liver weight, and fatty acid concentrations were determined. A Δ6‐desaturase index was calculated, and adipose tissue prostaglandin E₂ (PGE₂) and leukotriene B₄ (LTB₄) concentrations were determined to confirm enzyme inhibition. Results: Inhibition of Δ6‐desaturase and cyclooxygenase were confirmed. CLA caused a loss of body fat (P < 0.001). The body fat loss was blocked (P = 0.08) by the Δ6‐desaturase inhibitor at a dose that decreased (P < 0.05) the calculated index. Aspirin and NDGA had no effect on body fat and did not interact with CLA. Discussion: Inhibition of Δ6‐desaturase prevented CLA from being able to cause a body fat loss. Therefore, a desaturated metabolite of CLA appears to be involved in the CLA antiobesity effect. This effect of CLA does not seem dependent upon cyclooxygenase. Because lipoxygenase activity was not blocked by NDGA, we cannot draw conclusions about its importance in mediating the antiobesity effect of CLA.     

A post‐GWAS confirming the SCD gene associated with milk medium‐ and long‐chain unsaturated fatty acids in Chinese Holstein population

The stearoyl‐CoA desaturase (delta‐9‐desaturase) gene encodes a key enzyme in the cellular biosynthesis of monounsaturated fatty acids. In our initial genome‐wide association study (GWAS) of Chinese Holstein cows, 19 SNPs fell in a 1.8‐Mb region (20.3–22.1 Mb) on chromosome 26 underlying the SCD gene and were highly significantly associated with C14:1 or C14 index. The aims of this study were to verify whether the SCD gene has significant genetic effects on milk fatty acid composition in dairy cattle. By resequencing the entire coding region of the bovine SCD gene, a total of six variations were identified, including three coding variations (g.10153G>A, g.10213T>C and g.10329C>T) and three intronic variations (g.6926A>G, g.8646G>A and g.16158G>C). The SNP in exon 3, g.10329C>T, was predicted to result in an amino acid replacement from alanine (GCG) to valine (GTG) in the SCD protein. An association study for 16 milk fatty acids using 346 Chinese Holstein cows with accurate phenotypes and genotypes was performed using the mixed animal model with the proc mixed procedure in sas 9.2. All six detected SNPs were revealed to be associated with six medium‐ and long‐chain unsaturated fatty acids (P = 0.0457 to P < 0.0001), specifically for C14:1 and C14 index (P = 0.0005 to P < 0.0001). Subsequently, strong linkage disequilibrium (D′ = 0.88–1.00) was observed among all six SNPs in SCD and the five SNPs (rs41623887, rs109923480, rs42090224, rs42092174 and rs42091426) within the 1.8‐Mb region identified in our previous GWAS, indicating that the significant association of the SCD gene with milk fatty acid content traits reduced the observed significant 1.8‐Mb chromosome region in GWAS. Haplotype‐based analysis revealed significant associations of the haplotypes encompassing the six SCD SNPs and one SNP (rs109923480) in a GWAS with C14:1, C14 index, C16:1 and C16 index (P = 0.0011 to P < 0.0001). In summary, our findings provide replicate evidence for our previous GWAS and demonstrate that variants in the SCD gene are significantly associated with milk fatty acid composition in dairy cattle, which provides clear evidence for an increased understanding of milk fatty acid synthesis and enhances opportunities to improve milk‐fat composition in dairy cattle.     

9 cis,11 trans conjugated linoleic acid (CLA) is synthesised and desaturated into conjugated 18:3 in bovine adipose tissues

Although endogenous synthesis of conjugated linoleic acid (CLA) in the mammary gland of lactating cows has been already well documented, no study has determined so far as to which tissue and/or organ is involved in CLA synthesis in the growing ruminant except one study showing that CLA synthesis does not occur in ruminant liver. In this context, adipose tissue appears to be a good candidate for endogenous synthesis of CLA in the growing ruminant. The aim of this study was to compare the respective metabolisms of 11trans 18:1 (vaccenic acid, VA) and 9cis,11trans 18:2 (rumenic acid) to that of stearic acid (the preferential substrate of Δ9 desaturase) in adipose tissues (subcutaneous, SC and intermuscular, IM) of six Charolais steers by using the in vitromethod of incubated tissue slices. Samples of SC and IM adipose tissues were incubated at 37°C for 16 h under an atmosphere of 95% O2/5% CO2 in a medium supplemented with 0.75 mM of fatty acid (FA) mixture (representative of circulating non-esterified FA) and 186 μM [1-14C]-18:0 or 58.6 μM [1-14C]-VA or 56 μM [1-14C]-9cis,11trans CLA. Viability of explants was verified by measuring metabolic functions (glucose uptake and glucose-6-phosphate dehydrogenase activity). After 16 h of incubation, FA uptake was similar for all FA (18:0, VA and 9cis,11trans 18:2) in both SC and IM adipose tissues (around 40%). Once in adipose tissue, all FA were preferentially esterified (>80% of cell FA) favouring neutral lipid synthesis (around 90% of esterified FA). Stearic acid was highly (27%) desaturated into oleic acid in SC adipose tissue whereas this desaturation was much lower (6.8%) in IM adipose tissue (P < 0.0001). VA was desaturated into 9cis,11trans CLA at a low extent of about 2.5% to 4.4% in both adipose tissues probably because of a limited affinity of Δ9 desaturase for VA. 9cis,11trans CLA was itself converted by desaturation into 6cis, 9cis,11trans 18:3 at the intensity of 10.8% and 14.5% of cell 9cis,11trans CLA in SC and IM adipose tissues, respectively. In conclusion, bovine adipose tissues of the growing ruminant were especially involved in the endogenous synthesis of CLA from VA and in its desaturation into conjugated derivative, mainly 6cis, 9cis,11trans 18:3, of which biological properties need to be elucidated.     

Identification of genetic associations of ECHS1 gene with milk fatty acid traits in dairy cattle

Our previous genome‐wide association study identified 83 genome‐wide significant SNPs and 20 novel promising candidate genes for milk fatty acids in Chinese Holstein. Among them, the enoyl‐CoA hydratase, short chain 1 (ECHS1) and enoyl‐CoA hydratase and 3‐hydroxyacyl CoA dehydrogenase (EHHADH) genes were located near two SNPs and one SNP respectively, and they play important roles in fatty acid metabolism pathways. We herein validated whether the two genes have genetic effects on milk fatty acid traits in dairy cattle. By re‐sequencing the full‐length coding region, partially adjacent introns and 3000 bp up/downstream flanking sequences, we identified 12 SNPs in ECHS1: two in exons, four in the 3′ flanking region and six in introns. The g.25858322C>T SNP results in an amino acid replacement from leucine to phenylalanine and changes the secondary structure of the ECHS1 protein, and single‐locus association analysis showed that it was significantly associated with three milk fatty acids (P = 0.0002–0.0013). The remaining 11 SNPs were found to be significantly associated with at least one milk fatty acid (P = <0.0001–0.0040). Also, we found that two haplotype blocks, consisting of nine and two SNPs respectively, were significantly associated with eight milk fatty acids (P = <0.0001–0.0125). However, none of polymorphisms was observed in the EHHADH gene. In conclusion, our findings are the first to indicate that the ECHS1 gene has a significant genetic impact on long‐chain unsaturated and medium‐chain saturated fatty acid traits in dairy cattle, although the biological mechanism is still undetermined and requires further in‐depth validation.     

The role of Δ6-desaturase acyl-carrier specificity in the efficient synthesis of long-chain polyunsaturated fatty acids in transgenic plants

The role of acyl‐CoA‐dependent Δ6‐desaturation in the heterologous synthesis of omega‐3 long‐chain polyunsaturated fatty acids was systematically evaluated in transgenic yeast and Arabidopsis thaliana. The acyl‐CoA Δ6‐desaturase from the picoalga Ostreococcus tauri and orthologous activities from mouse (Mus musculus) and salmon (Salmo salar) were shown to generate substantial levels of Δ6‐desaturated acyl‐CoAs, in contrast to the phospholipid‐dependent Δ6‐desaturases from higher plants that failed to modify this metabolic pool. Transgenic plants expressing the acyl‐CoA Δ6‐desaturases from either O. tauri or salmon, in conjunction with the two additional activities required for the synthesis of C20 polyunsaturated fatty acids, contained higher levels of eicosapentaenoic acid compared with plants expressing the borage phospholipid‐dependent Δ6‐desaturase. The use of acyl‐CoA‐dependent Δ6‐desaturases almost completely abolished the accumulation of unwanted biosynthetic intermediates such as γ‐linolenic acid in total seed lipids. Expression of acyl‐CoA Δ6‐desaturases resulted in increased distribution of long‐chain polyunsaturated fatty acids in the polar lipids of transgenic plants, reflecting the larger substrate pool available for acylation by enzymes of the Kennedy pathway. Expression of the O. tauriΔ6‐desaturase in transgenic Camelina sativa plants also resulted in the accumulation of high levels of Δ6‐desaturated fatty acids. This study provides evidence for the efficacy of using acyl‐CoA‐dependent Δ6‐desaturases in the efficient metabolic engineering of transgenic plants with high value traits such as the synthesis of omega‐3 LC‐PUFAs.     

The heparan and heparin metabolism pathway is involved in regulation of fatty acid composition

Six genes involved in the heparan sulfate and heparin metabolism pathway, DSEL (dermatan sulfate epimerase-like), EXTL1 (exostoses (multiple)-like 1), HS6ST1 (heparan sulfate 6-O-sulfotransferase 1), HS6ST3 (heparan sulfate 6-O-sulfotransferase 3), NDST3 (N-deacetylase/N-sulfotransferase (heparan glucosaminyl) 3), and SULT1A1 (sulfotransferase family, cytosolic, 1A, phenol-preferring, member 1), were investigated for their associations with muscle lipid composition using cattle as a model organism. Nineteen single nucleotide polymorphisms (SNPs)/multiple nucleotide length polymorphisms (MNLPs) were identified in five of these six genes. Six of these mutations were then genotyped on 246 Wagyu x Limousin F(2) animals, which were measured for 5 carcass, 6 eating quality and 8 fatty acid composition traits. Association analysis revealed that DSEL, EXTL1 and HS6ST1 significantly affected two stearoyl-CoA desaturase activity indices, the amount of conjugated linoleic acid (CLA), and the relative amount of saturated fatty acids (SFA) and monounsaturated fatty acids (MUFA) in skeletal muscle (P<0.05). In particular, HS6ST1 joined our previously reported SCD1 and UQCRC1 genes to form a three gene network for one of the stearoyl-CoA desaturase activity indices. These results provide evidence that genes involved in heparan sulfate and heparin metabolism are also involved in regulation of lipid metabolism in bovine muscle. Whether the SNPs affected heparan sulfate proteoglycan structure is unknown and warrants further investigation.     

Influence of roughage/concentrate ratio and linseed oil on the concentration of trans-fatty acids and conjugated linoleic acid in duodenal chyme and milk fat of late lactating cows

Abstract

The objective of the study was to investigate the influence of two roughage-to-concentrate ratios, with or without linseed oil supplementation, on the flow of fatty acids in the intestinal chyme and the secretion in milk fat in late lactating cows. Seven late lactating cows fitted with cannulae in the dorsal rumen and simple T-shaped cannulae in the proximal duodenum were randomly assigned to four experimental periods applying an incomplete replicated 2×2 Latin square design. The rations consisted of meadow hay and a concentrate mixture given in a ratio of 70 : 30 or 30 : 70 on dry matter basis. The basal rations were fed without or with 200 g linseed oil daily. After three weeks of adaptation, samples from the duodenal chyme were taken to study the flow of fatty acids. Additionally, milk samples were analysed for their milk fat composition. Decreasing roughage/concentrate ratio and linseed oil supplementation significantly increased the flow of monounsaturated fatty acids (MUFA), trans-fatty acids (tFA) and conjugated linoleic acids (CLA) in the duodenum. Furthermore, linseed oil increased the flow of saturated fatty acids (SFA) in the duodenum. Higher concentrate portion (H 30) and linseed oil supplementation significantly decreased the milk fat content. SFA were lower (p < 0.05) and MUFA were higher (p < 0.05) in milk fat after linseed oil supplementation; H 30 resulted in more polyunsaturated fatty acids (PUFA, p < 0.05) in the milk. Linseed oil supplementation significantly increased tFA and CLA in milk fat. The higher CLA content in milk fat as compared to that in the digesta suggests that a substantial endogenous synthesis of CLA in the mammary gland tissue through Δ9-desaturase took place. Between 21% and 48% of duodenal t11-C_18:1 were converted into c9, t11-CLA in milk fat.     

t-10, c-12 CLA Dietary Supplementation Inhibits Atherosclerotic Lesion Development Despite Adverse Cardiovascular and Hepatic Metabolic Marker Profiles

Animal and human studies have indicated that fatty acids such as the conjugated linoleic acids (CLA) found in milk could potentially alter the risk of developing metabolic disorders including diabetes and cardiovascular disease (CVD). Using susceptible rodent models (apoE^−/− and LDLr^−/− mice) we investigated the interrelationship between mouse strain, dietary conjugated linoleic acids and metabolic markers of CVD. Despite an adverse metabolic risk profile, atherosclerosis (measured directly by lesion area), was significantly reduced with t-10, c-12 CLA and mixed isomer CLA (Mix) supplementation in both apoE^−/− (p<0.05, n = 11) and LDLr^−/− mice (p<0.01, n = 10). Principal component analysis was utilized to delineate the influence of multiple plasma and tissue metabolites on the development of atherosclerosis. Group clustering by dietary supplementation was evident, with the t-10, c-12 CLA supplemented animals having distinct patterns, suggestive of hepatic insulin resistance, regardless of mouse strain. The effect of CLA supplementation on hepatic lipid and fatty acid composition was explored in the LDLr^−/− strain. Dietary supplementation with t-10, c-12 CLA significantly increased liver weight (p<0.05, n = 10), triglyceride (p<0.01, n = 10) and cholesterol ester content (p<0.01, n = 10). Furthermore, t-10, c-12 CLA also increased the ratio of 18∶1 to 18∶0 fatty acid in the liver suggesting an increase in the activity of stearoyl-CoA desaturase. Changes in plasma adiponectin and liver weight with t-10, c-12 CLA supplementation were evident within 3 weeks of initiation of the diet. These observations provide evidence that the individual CLA isomers have divergent mechanisms of action and that t-10, c-12 CLA rapidly changes plasma and liver markers of metabolic syndrome, despite evidence of reduction in atherosclerosis.     

Effect of dietary conjugated linoleic acid and selenized yeast on the concentration of fatty acids and minerals in rats

Abstract

The main objective of this study was to evaluate the influence of diets enriched in individual conjugated linoleic acid (CLA) isomers, their mixture, and/or selenized yeast (Se-yeast) on the concentration of CLA isomers, long-chain polyunsaturated fatty acids (PUFA) and Se in the heart, muscles and liver of rats. The investigation was performed on 73 female Wistar rats (8 weeks of age, 200 g initial BW). After one week sub-maintenance feeding, rats received diets supplemented with 1% individual CLA isomers or 1 or 2% of a CLA isomers mixture, without or with 1.2 mg Se/kg (as Se-yeast) for 29 days. Feeding diets with 2% CLA isomer mixture reduced feed intake and body weight gain of rats, while addition of trans10,cis12 CLA and Se-yeast resulted in the highest body weight gain. CLA supplementation generally elevated the concentration of CLA isomers in heart and muscles significantly, although cis9,trans11 CLA accumulated preferentially. Regardless of the presence of Se-yeast, the dietary enrichment with CLA isomers caused a reduction in the capacity of Δ9-desaturase. Addition of Se-yeast to diets with individual CLA isomers or a 1% mixture of CLA isomers elevated the accumulation of CLA isomers in the heart and muscles, whereas all treatments with supplemented CLA and Se-yeast increased the accumulation of Se in rats compared with animals fed the diet containing Se only. Furthermore, CLA isomer supplementation decreased the concentration of PUFA and total fatty acids in the heart and muscles compared with control rats. Moreover, addition of CLA isomers interfered in the conversion of linoleic and linolenic acids to higher metabolites due to competition of CLA isomers for the same enzymes (Δ6-, Δ5-, Δ4-desaturases and elongase).     

Genome Wide Association Study Identifies 20 Novel Promising Genes Associated with Milk Fatty Acid Traits in Chinese Holstein

Detecting genes associated with milk fat composition could provide valuable insights into the complex genetic networks of genes underling variation in fatty acids synthesis and point towards opportunities for changing milk fat composition via selective breeding. In this study, we conducted a genome-wide association study (GWAS) for 22 milk fatty acids in 784 Chinese Holstein cows with the PLINK software. Genotypes were obtained with the Illumina BovineSNP50 Bead chip and a total of 40,604 informative, high-quality single nucleotide polymorphisms (SNPs) were used. Totally, 83 genome-wide significant SNPs and 314 suggestive significant SNPs associated with 18 milk fatty acid traits were detected. Chromosome regions that affect milk fatty acid traits were mainly observed on BTA1, 2, 5, 6, 7, 9, 13, 14, 18, 19, 20, 21, 23, 26 and 27. Of these, 146 SNPs were associated with more than one milk fatty acid trait; most of studied fatty acid traits were significant associated with multiple SNPs, especially C18:0 (105 SNPs), C18 index (93 SNPs), and C14 index (84 SNPs); Several SNPs are close to or within the DGAT1, SCD1 and FASN genes which are well-known to affect milk composition traits of dairy cattle. Combined with the previously reported QTL regions and the biological functions of the genes, 20 novel promising candidates for C10:0, C12:0, C14:0, C14:1, C14 index, C18:0, C18:1n9c, C18 index, SFA, UFA and SFA/UFA were found, which composed of HTR1B, CPM, PRKG1, MINPP1, LIPJ, LIPK, EHHADH, MOGAT1, ECHS1, STAT1, SORBS1, NFKB2, AGPAT3, CHUK, OSBPL8, PRLR, IGF1R, ACSL3, GHR and OXCT1. Our findings provide a groundwork for unraveling the key genes and causal mutations affecting milk fatty acid traits in dairy cattle.     

ISOLATION OF THREE NOVEL LONG‐CHAIN POLYUNSATURATED FATTY ACID Δ9‐ELONGASES AND THE TRANSGENIC ASSEMBLY OF THE ENTIRE PAVLOVA SALINA DOCOSAHEXAENOIC ACID PATHWAY IN NICOTIANA BENTHAMIANA1

The transgenic aerobic synthesis of long‐chain polyunsaturated fatty acids (LC‐PUFA) will in most land plants commence with either a Δ6‐desaturation or a Δ9‐elongation. Numerous Δ6‐desaturases have been characterized, but only one Δ9‐elongase has been reported in peer‐reviewed literature. In the present study, we describe the isolation of three additional Δ9‐elongases from the class Haptophyceae and demonstrate that the Δ9‐elongase group contains highly conserved regions, which differentiate them from other ELO‐type elongases. One such important difference is the presence of an LQxFHH motif instead of the usual LHxYHH motif, a feature that should simplify further gene discovery efforts in this group of enzymes. Moreover, the identification of the Pavlova salina (N. Carter) J. C. Green Δ9‐elongase completes the isolation of the entire P. salina docosahexaenoic acid (DHA) pathway, and we describe the assembly of this pathway in Nicotiana benthamiana. Finally, we comment on possible explanations for the widespread presence of the Δ6‐desaturated fatty acid stearidonic acid (SDA, 18:4^Δ6,9,12,15) in the plastidial lipids of organisms using the Δ9‐elongase pathway.     

The role of Delta(9)-desaturase in the production of cis-9, trans-11 CLA

Biomedical studies with animal models have demonstrated that cis-9, trans-11 conjugated linoleic acid (CLA), the predominant isomer found in milk fat from dairy cows, has anticarcinogenic effects. We recently demonstrated endogenous synthesis of cis-9, trans-11 CLA from ruminally derived trans-11 C18:1 by Delta(9)-desaturase in lactating dairy cows. The present study further examined endogenous synthesis of cis-9, trans-11 CLA and quantified its importance by increasing substrate supply using partially hydrogenated vegetable oil (PHVO) as a source of trans-11 C18:1 and blocking endogenous synthesis using sterculic oil (SO) as a source of cyclopropene fatty acids which specifically inhibit Delta(9)-desaturase. Four cows were abomasally infused with 1) control, 2) PHVO, 3) SO, and 4) PHVO+SO in a 4 x 4 Latin square design. With infusion of PHVO, cis-9, trans-11 CLA was increased by 17% in milk fat. Consistent with inhibition of desaturase, SO treatments increased milk fat ratios for the fatty acid pairs effected by Delta(9)-desaturase, C14:0/cis-9 C14:1, C16:0/cis-9 C16:1, and C18:0/cis-9 C18:1. The role of endogenous synthesis of CLA was evident from the 60-65% reduction in cis-9, trans-11 CLA which occurred in milk fat with SO treatments. cis-9 C14:1 originates from desaturation of C14:0 by Delta(9)-desaturase and can be used to estimate the extent of SO inhibition of Delta(9)-desaturase. When this correction factor was applied, endogenous synthesis was estimated to account for 78% of the total cis-9, trans-11 CLA in milk fat. Thus, endogenous synthesis was the major source of cis-9, trans-11 CLA in milk fat of lactating cows.     

Chemical evaluation of fatty acid desaturases as drug targets in Trypanosoma cruzi

Four positional isomers of Thiastearate (TS) and Isoxyl (Thiocarlide) were assayed as fatty acid desaturase inhibitors in Trypanosoma cruzi epimastigotes. 9-TS did not exert a significant effect on growth of T. cruzi, nor on the fatty acid profile of the parasite cells. One hundred micromolars of 10-TS totally inhibited growth, with an effective concentration for 50% growth inhibition (EC₅₀) of 3.0 ± 0.2 μM. Growth inhibition was reverted by supplementing the culture media with oleate. The fatty acid profile of treated cells revealed that conversion of stearate to oleate and palmitate to palmitoleate were drastically reduced and, as a consequence, the total level of unsaturated fatty acids decreased from 60% to 32%. Isoxyl, a known inhibitor of stearoyl-CoA Δ9 desaturase in mycobacteria, had similar effects on T. cruzi growth (EC₅₀ 2.0 ± 0.3 μM) and fatty acid content, indicating that Δ9 desaturase was the target of both drugs. 12- and 13-TS were inhibitors of growth with EC₅₀ values of 50 ± 2 and 10 ± 3 μM, respectively, but oleate or linoleate were unable to revert the effect. Both drugs increased the percentage of oleate and palmitate in the cell membrane and drastically reduced the content of linoleate from 38% to 16% and 12%, respectively, which is in agreement with a specific inhibition of oleate Δ12 desaturase. The absence of corresponding enzyme activity in mammalian cells and the significant structural differences between trypanosome and mammalian Δ9 desaturases, together with our results, highlight these enzymes as promising targets for selective chemotherapeutic intervention.     

Identification of the conjugated linoleic acid isomer that inhibits milk fat synthesis

Conjugated linoleic acids (CLA) are octadecadienoic fatty acids that have profound effects on lipid metabolism. Our previous work showed that CLA (mixture of isomers) markedly reduced milk fat synthesis. In this study, our objective was to evaluate the effects of specific CLA isomers. Multiparous Holstein cows were used in a 3x3 Latin square design, and treatments were 4-day abomasal infusions of 1) skim milk (control), 2) 9,11 CLA supplement, and 3) 10,12 CLA supplement. CLA supplements provided 10 g/day of the specific CLA isomer (cis-9,trans-11 or trans-10,cis-12). Treatments had no effect on intake, milk yield, or milk protein yield. Only the 10,12 CLA supplement affected milk fat, causing a 42 and 44% reduction in milk fat percentage and yield, respectively. Milk fat composition revealed that de novo synthesized fatty acids were extensively reduced. Increases in ratios of C(14:0) to C(14:1) and C(18:0) to C(18:1) indicated the 10,12 CLA supplement also altered Delta(9)-desaturase. Treatments had minimal effects on plasma concentrations of glucose, nonesterified fatty acids, insulin, or insulin-like growth factor-I. Overall, results demonstrate that trans-10,cis-12 CLA is the isomer responsible for inhibition of milk fat synthesis.     

Influence of roughage/concentrate ratio and linseed oil on the concentration of trans-fatty acids and conjugated linoleic acid in duodenal chyme and milk fat of late lactating cows

The objective of the study was to investigate the influence of two roughage-to-concentrate ratios, with or without linseed oil supplementation, on the flow of fatty acids in the intestinal chyme and the secretion in milk fat in late lactating cows. Seven late lactating cows fitted with cannulae in the dorsal rumen and simple T-shaped cannulae in the proximal duodenum were randomly assigned to four experimental periods applying an incomplete replicated 2 x 2 Latin square design. The rations consisted of meadow hay and a concentrate mixture given in a ratio of 70:30 or 30:70 on dry matter basis. The basal rations were fed without or with 200 g linseed oil daily. After three weeks of adaptation, samples from the duodenal chyme were taken to study the flow of fatty acids. Additionally, milk samples were analysed for their milk fat composition. Decreasing roughage/concentrate ratio and linseed oil supplementation significantly increased the flow of monounsaturated fatty acids (MUFA), trans-fatty acids (tFA) and conjugated linoleic acids (CLA) in the duodenum. Furthermore, linseed oil increased the flow of saturated fatty acids (SFA) in the duodenum. Higher concentrate portion (H 30) and linseed oil supplementation significantly decreased the milk fat content. SFA were lower (p < 0.05) and MUFA were higher (p < 0.05) in milk fat after linseed oil supplementation; H 30 resulted in more polyunsaturated fatty acids (PUFA, p < 0.05) in the milk. Linseed oil supplementation significantly increased tFA and CLA in milk fat. The higher CLA content in milk fat as compared to that in the digesta suggests that a substantial endogenous synthesis of CLA in the mammary gland tissue through A9-desaturase took place. Between 21% and 48% of duodenal t11-C(18:1) were converted into c9, t11-CLA in milk fat.     

Redirection of metabolic flux for high levels of omega‐7 monounsaturated fatty acid accumulation in camelina seeds

Seed oils enriched in omega‐7 monounsaturated fatty acids, including palmitoleic acid (16:1?9) and cis‐vaccenic acid (18:1?11), have nutraceutical and industrial value for polyethylene production and biofuels. Existing oilseed crops accumulate only small amounts (<2%) of these novel fatty acids in their seed oils. We demonstrate a strategy for enhanced production of omega‐7 monounsaturated fatty acids in camelina (Camelina sativa) and soybean (Glycine max) that is dependent on redirection of metabolic flux from the typical ?9 desaturation of stearoyl (18:0)‐acyl carrier protein (ACP) to ?9 desaturation of palmitoyl (16:0)‐acyl carrier protein (ACP) and coenzyme A (CoA). This was achieved by seed‐specific co‐expression of a mutant ?9‐acyl‐ACP and an acyl‐CoA desaturase with high specificity for 16:0‐ACP and CoA substrates, respectively. This strategy was most effective in camelina where seed oils with ~17% omega‐7 monounsaturated fatty acids were obtained. Further increases in omega‐7 fatty acid accumulation to 60–65% of the total fatty acids in camelina seeds were achieved by inclusion of seed‐specific suppression of 3‐keto‐acyl‐ACP synthase II and the FatB 16:0‐ACP thioesterase genes to increase substrate pool sizes of 16:0‐ACP for the ?9‐acyl‐ACP desaturase and by blocking C18 fatty acid elongation. Seeds from these lines also had total saturated fatty acids reduced to ~5% of the seed oil versus ~12% in seeds of nontransformed plants. Consistent with accumulation of triacylglycerol species with shorter fatty acid chain lengths and increased monounsaturation, seed oils from engineered lines had marked shifts in thermotropic properties that may be of value for biofuel applications.     

Effects of dietary sources of vegetable fats on performance of dairy ewes and conjugated linoleic acid (CLA) in milk

Two experiments were carried out to study the effects of supplementing the ration of lactating ewes with vegetable fats (sunflower oil, SO or hydrogenated palm oil, HPO; HIDROPALM^®) on diet digestibility, milk yield and milk composition, and on the concentration of the conjugated linoleic acid (CLA) C18:2 cis-9 trans-11 and C18:1 trans-11 (vaccenic acid, VA) and other main fatty acids in milk fat. Treatments involved a control diet, without added oil, and 2 diets supplemented with either 12 g/kg SO or 12 g/kg HPO on a dry matter (DM) basis. In the first experiment, 6 non-pregnant, non-lactating Lacaune ewes were used following a 3 × 3 replicated Latin Square design. Addition of vegetable fat supplement to the diet increased digestibility of DM, organic matter (OM) and crude protein (CP), but did not affect that of the ether extract (EE), neutral detergent fibre (NDF) or acid detergent fibre (ADF). In the second experiment, 60 Lacaune dairy ewes mid-way through lactation (120 ± 12 days in milk, 0.98 ± 0.03 kg/day average milk yield) were divided into three equal-sized groups each of which was assigned to one of the three experimental diets for 4 weeks. Compared with the control treatment, supplementation with HPO increased milk yield and energy-corrected milk. But neither vegetable fat supplement modified percentages of fat and protein in milk. Supplementation with HPO increased C14:1, C16:1 and C16:0 content and reduced C18:0 and C18:1 cis-9 content in milk fat. Supplementation with SO increased the VA content in milk fat by 36% and that of cis-9 trans-11 CLA by 29% in comparison with the control diet. Supplementation with HPO led to milk fat with 15% more cis-9 trans-11 CLA than control milk. In conclusion, adding a moderate dose of HPO or SO to the diets increased CLA concentration in milk fat. Nevertheless, supplementation with SO was more effective than HPO in increasing CLA concentration in milk fat and reducing the atherogenicity index, improving milk quality from the human health standpoint.