Ring position in cyclopropene fatty acids and stearic acid desaturation in hen liver

The effects of dietary cottonseed meal and oil supplementation on laying performance and egg quality of laying hens

Cottonseed meal (CSM) and cottonseed oil (CSO), two cottonseed products, are rich in protein and lipids, respectively, but their use is limited by antinutritional factors in the products. This study investigated the effect of different dietary levels of CSM and CSO supplementation on the laying performance and egg quality of laying hens. A total of 162 24-week-old Hy-Line brown laying hens were randomly assigned to diets supplemented with 0, 6%, or 12% CSM and 0, 2%, or 4% CSO in a 3 × 3 factorial design. During the 8-week feeding trial, laying performance and egg quality parameters were measured weekly. Furthermore, a texture profile analysis (TPA) of the egg yolks was conducted, and the fatty acid profiles and protein composition of the yolks were measured to further determine egg quality. CSM supplementation decreased (p < 0.01) egg production and feed efficiency and increased (p < 0.01) yolk color, eggshell rate, and shell thickness, but had no significant effects on the TPA parameters, fatty acid profiles, and protein components of egg yolks. CSO supplementation resulted in decreases (p < 0.01) in egg production, egg weight, and feed efficiency and an increase (p < 0.01) in yolk color. In addition, CSO supplementation with two weeks of cold storage changed the physical properties of boiled egg yolks, as indicated by increased (p < 0.01) hardness, springiness, cohesiveness, and chewiness. Furthermore, 4% CSO supplementation increased the ratio of saturated/monounsaturated fatty acids (SAFA/MUFA) and the protein content of egg yolks, which was accompanied by a modified protein composition. These results indicate that CSM supplementation reduces laying performance and egg quality, and CSO supplementation decreases laying performance and results in egg yolk hardening by modifying its components.

Characterization and analysis of the cotton cyclopropane fatty acid synthase family and their contribution to cyclopropane fatty acid synthesis

BACKGROUND

Cyclopropane fatty acids (CPA) have been found in certain gymnosperms, Malvales, Litchi and other Sapindales. The presence of their unique strained ring structures confers physical and chemical properties characteristic of unsaturated fatty acids with the oxidative stability displayed by saturated fatty acids making them of considerable industrial interest. While cyclopropenoid fatty acids (CPE) are well-known inhibitors of fatty acid desaturation in animals, CPE can also inhibit the stearoyl-CoA desaturase and interfere with the maturation and reproduction of some insect species suggesting that in addition to their traditional role as storage lipids, CPE can contribute to the protection of plants from herbivory.

RESULTS

Three genes encoding cyclopropane synthase homologues GhCPS1, GhCPS2 and GhCPS3 were identified in cotton. Determination of gene transcript abundance revealed differences among the expression of GhCPS1, 2 and 3 showing high, intermediate and low levels, respectively, of transcripts in roots and stems; whereas GhCPS1 and 2 are both expressed at low levels in seeds. Analyses of fatty acid composition in different tissues indicate that the expression patterns of GhCPS1 and 2 correlate with cyclic fatty acid (CFA) distribution. Deletion of the N-terminal oxidase domain lowered GhCPS's ability to produce cyclopropane fatty acid by approximately 70%. GhCPS1 and 2, but not 3 resulted in the production of cyclopropane fatty acids upon heterologous expression in yeast, tobacco BY2 cell and Arabidopsis seed.

CONCLUSIONS

In cotton GhCPS1 and 2 gene expression correlates with the total CFA content in roots, stems and seeds. That GhCPS1 and 2 are expressed at a similar level in seed suggests both of them can be considered potential targets for gene silencing to reduce undesirable seed CPE accumulation. Because GhCPS1 is more active in yeast than the published Sterculia CPS and shows similar activity when expressed in model plant systems, it represents a strong candidate gene for CFA accumulation via heterologous expression in production plants.

Oleic acid biosynthesis in Plasmodium falciparum: characterization of the stearoyl-CoA desaturase and investigation as a potential therapeutic target

Background

Plasmodium falciparum parasitization of erythrocytes causes a substantial increase in the levels of intracellular fatty acids, notably oleic acid. How parasites acquire this monounsaturated fatty acid has remained enigmatic. Here, we report on the biochemical and enzymatic characterization of stearoyl-CoA desaturase (SCD) in P. falciparum.

Methodology/Principal Findings

Metabolic labeling experiments allowed us to demonstrate the production of oleic acid from stearic acid both in lysates of parasites incubated with [¹⁴C]-stearoyl-CoA and in parasite-infected erythrocytes labeled with [¹⁴C]-stearic acid. Optimal SCD activity was detected in schizonts, the stage of maximal membrane synthesis. This activity correlated with a late trophozoite stage-specific induction of PFE0555w transcripts. PFE0555w harbors a typical SCD signature. Similar to mammalian SCDs, this protein was found to be associated with the endoplasmic reticulum, as determined with PFE0555w-GFP tagged transgenic P. falciparum. Importantly, these parasites exhibited increased rates of stearic to oleic acid conversion, providing additional evidence that PFE0555w encodes the plasmodial SCD (PfSCD). These findings prompted us to assess the activity of sterculic acid analogues, known to be specific Δ9-desaturase inhibitors. Methyl sterculate inhibited the synthesis of oleic acid both with parasite lysates and infected erythrocytes, most likely by targeting PfSCD. This compound exhibited significant, rapid and irreversible antimalarial activity against asexual blood stages. This parasiticidal effect was antagonized by oleic acid.

Conclusion/Significance

Our study provides evidence that parasite-mediated fatty acid modification is important for blood-stage survival and provides a new strategy to develop a novel antimalarial therapeutic based on the inhibition of PfSCD.

Inhibition of the acyl-CoA desaturases involved in the biosynthesis of Spodoptera littoralis sex pheromone by analogs of 10,11-methylene-10-tetradecenoic acid

The desaturase inhibitory activity of the cyclopropenyl alcohols 9,10-methylene-9-tetradecen-1-ol (9-MTOL), 10,11-methylene-10-tetradecen-1-ol (10-MTOL) and 11,12-methylene-11-tetradecen-1-ol (11-MTOL), which are structural analogs of 10,11-methylene-10-tetradecenoic acid (10-MTA), is reported. At equimolar ratios with respect to the different substrates, the three compounds completely inhibited the three desaturation reactions involved in the biosynthesis of Spodoptera littoralis sex pheromone. The dose-dependence of inhibition was determined for 10-MTA and its alcohol derivative. Both compounds inhibited the transformation of perdeuterated palmitic acid into perdeuterated (Z)-11-hexadecenoic acid and that of (E)-11-tridecenoic acid into (Z,E)-9,11-tridecadienoic acid with similar IC(50) values. The overall results presented in this work support scattered data that neither the free carboxyl groups nor their acyl-CoA esters are a requisite for inhibition of desaturases. Since the synthesis of cyclopropenols is much more convenient than that of cyclopropene fatty acids, this finding is of economical relevance regarding the putative use of cyclopropene derivatives in pest control.

Characterization of cyclopropane fatty-acid synthase from Sterculia foetida

Cyclopropane synthase from Sterculia foetida developing seeds catalyzes the addition of a methylene group from S-adenosylmethionine to the cis double bond of oleic acid (Bao, X., Katz, S., Pollard, M., and Ohlrogge, J. (2002) Proc. Natl. Acad. Sci. U. S. A. 99, 7172-7177). To understand this enzyme better, differential expression in leaf and seed tissues, protein properties, and substrate preferences of plant cyclopropane synthase were investigated. Immunoblot analysis with antibodies raised to recombinant S. foetida cyclopropane synthase (SfCPA-FAS) revealed that SfCPA-FAS is expressed in S. foetida seeds, but not in leaves, and is a membrane protein localized to microsomal fractions. Transformed tobacco cells expressing SfCPA-FAS were labeled in vivo with L-[methyl-(14)C]methionine and assayed in vitro with S-adenosyl-L-[methyl-(14)C]methionine. These kinetic experiments demonstrated that dihydrosterculate was synthesized from oleic acid esterified at the sn-1 position of phosphatidylcholine (PC). Furthermore, analysis of acyl chains at sn-1 and sn-2 positions that accumulated in PC from S. foetida developing seeds and from tobacco cells expressing SfCPA-FAS also demonstrated that greater than 90% of dihydrosterculate was esterified to the sn-1 position. Thus, we conclude that SfCPA-FAS is a microsomal localized membrane protein that catalyzes the addition of methylene groups derived from S-adenosyl-L-methionine across the double bond of oleic acid esterified to the sn-1 position of PC. A survey of plant and bacterial genomes for sequences related to SfCPA-FAS indicated that a peptide domain with a putative flavin-binding site is either fused to the methyltransferase domain of the plant protein or is often found encoded by a gene adjacent to a bacterial cyclopropane synthase gene.

Carbocyclic fatty acids in plants: biochemical and molecular genetic characterization of cyclopropane fatty acid synthesis of Sterculiafoetida

Fatty acids containing three-member carbocyclic rings are found in bacteria and plants. Bacteria synthesize cyclopropane fatty acids (CPA-FAs) only by the addition of a methylene group from S-adenosylmethionine to the cis-double bond of monoenoic phospholipid-bound fatty acids. In plants CPA-FAs are usually minor components with cyclopropene fatty acids (CPE-FAs) more abundant. Sterculia foetida seed oil contains 65-78% CPE-FAs, principally sterculic acid. To address carbocyclic fatty acid synthesis in plants, a cDNA library was constructed from developing seeds during the period of maximum oil deposition. About 0.4% of 5,300 expressed sequence tags were derived from one gene, which shared similarities to the bacterial CPA-FA synthase. However, the predicted protein is twice as large as the bacterial homolog and represents a fusion of an FAD-containing oxidase at the N terminus and a methyltransferase at the C terminus. Functional analysis of the isolated full-length cDNA was conducted in tobacco suspension cells where its expression resulted in the accumulation of up to 6.2% dihydrosterculate of total fatty acids. In addition, the dihydrosterculate was specifically labeled by [methyl-(14)C]methionine and by [(14)C]oleic acid in the transgenic tobacco cells. In in vitro assay of S. foetida seed extracts, S-adenosylmethionine served as a methylene donor for the synthesis of dihydrosterculate from oleate. Dihydrosterculate accumulated largely in phosphatidylcholine in both systems. Together, a CPA-FA synthase was identified from S. foetida, and the pathway in higher plants that produce carbocyclic fatty acids was defined as by transfer of C(1) units, most likely from S-adenosylmethionine to oleate.

Altered lipid metabolism and impaired clearance of plasma cholesterol in mice fed cyclopropenoid fatty acids

Swiss-Webster mice fed a diet containing 0.5% cyclopropenoid fatty acids (CPFA) for 6 weeks showed depressed growth rates and developed hypercholesteremia and increased concentrations of serum phospholipid and free cholesterol compared to control mice. No depression of cytochromes P-450 and b5 or microsomal mixed-function oxidase activities occurred to indicate impaired oxidative catabolism of serum cholesterol. Elimination of intragastrically administered [3H]cholesterol from blood was biphasic; there was no significant difference in first-order rate constants for absorption, distribution, and elimination processes between control and CPFA-fed animals. However, the area under the blood clearance curve for CPFA-fed animals was significantly increased (p less than or equal to 0.01) by 29% over controls, demonstrating a net increase in clearance time for exogenous cholesterol in CPFA-fed animals, thus contributing to their hypercholesteremia. In the CPFA-fed mice, the percentage of saturated fatty acid residues increased at the expense of monounsaturates in the cholesterol ester, triglyceride, and phosphatidyl choline fractions of serum lipids. Total polyene content of serum lipid was not altered; however, CPFA-fed animals demonstrated increased linoleic acid at the expense of arachidonic acid in all serum lipid fractions. Excessively saturated serum lipids may impede clearance of serum cholesterol in CPFA-fed animals by inhibited plasma lecithin-cholesterol acyltransferase (LCAT) and hepatic cholesterol esterase activities.

Reduction of hepatic stearoyl-CoA desaturase activity in rats fed iron-deficient diets

The effect of feeding iron-deficient diets to rats on the hepatic stearoyl-CoA desaturase activity was examined since iron is present in the delta 9 desaturation system. Separate groups of rats were fed low iron diets without fat (FF-Fe) or containing either 14% hydrogenated coconut oil (HCNO-Fe) or 14% corn oil (CO-Fe) for 10 weeks. Diets supplemented with iron (FF + Fe, HCNO + Fe and CO + Fe) were fed to the corresponding control groups. Stearoyl-CoA desaturase activity in the liver microsomes of rats in the CO + Fe group (2.55 +/- 0.17 nmol oleate produced/min/mg protein) was about half of that in the HCNO + Fe (4.76 +/- 0.15) and FF + Fe (5.38 +/- 0.18) diet groups. In rats which were fed iron-deficient diets, hepatic desaturase levels were reduced significantly as compared to those of controls (1.0 +/- 0.06, CO-Fe; 2.11 +/- 0.13, HCNO-Fe; 3.65 +/- 0.1, FF-Fe). The hemoglobin (Hb) and hematocrit (Hct) levels in blood showed moderate iron depletion only in the CO-Fe group. Hence, dietary polyunsaturated fat promotes the onset of iron deficiency. Furthermore, even before the blood Hb and Hct values express iron depletion, the effect of feeding low iron diets was observed by the reduction of hepatic delta 9 desaturase activity in rats fed HCNO-Fe and FF-Fe diets.

The effect of dietary methyl branched-chain fatty acids on aspects of hepatic lipid metabolism in the rat

1. Rats were fed to appetite on a stock laboratory diet or on diets consisting of the stock diet and in addition 50 or 200 g triolein/kg, 50 g palmitic acid/kg or 50 g/kg of a concentrate mixture of methyl branched-chain fatty acids (Me-BCFA) which had been prepared from sheep adipose triacylglycerols. 2. No differences could be detected in the delta 9-desaturase activity or fatty acid synthetase activity of liver preparations from rats which had been fed on either the stock diet, the 50 g palmitic acid/kg or the 50 and 200 g triolein/kg diet; the palmitic acid diet was therefore taken as the control diet in subsequent experiments. 3. Rats consuming the 50 g Me-BCFA/kg diet exhibited a marked reduction in the capacity of their liver microsomes for delta 9-desaturation when compared with animals receiving the control diet. The delta 6-desaturase activity also showed an inhibitory trend with the Me-BCFA diet. 4. Microsomal omega-oxidation of fatty acids, mitochondrial succinate oxidation and the activity of cytosolic fatty acid synthetase (FAS) were unaffected by the ingestion of the Me-BCFA mixture compared with the diet which included palmitic acid. 5. There were no differences in the plasma concentration of thyroxin, insulin and glucagon between animals fed on the diets containing palmitic acid or the Me-BCFA. 6. For a given concentration of fatty acids the Me-BCFA had a greater inhibitory effect when added to incubations of liver microsomes from rats fed on the standard diet than did the addition of palmitic acid. 7. The observations in vivo and in vitro strongly suggested that the Me-BCFA were having a specific inhibitory effect on the desaturation reaction.

Reduction of essential fatty acid deficiency in rat fed a low iron fat free diet

Young male rats were fed ad libitum for 8 weeks a low iron fat-free (FF-Fe) diet or a fat-free diet supplemented with iron (FF+Fe). The relative levels of 16:1 and 18:1 to 18:0 in the total fatty acids of liver and other tissues (plasma, erythrocytes and intestinal mucosa) were considerably decreased because of a lack of dietary iron. In rats fed the FF-Fe diet, the levels of essential fatty acids (18:2 omega 6 + 20:4 omega 6) in tissues were 2- to 3-fold greater than in the corresponding tissues of rats fed the FF+Fe diet. Eicosatrienoic acid (20:3 omega 9) levels in tissue lipids from rats fed the FF+Fe diet were high (8-16%), whereas they were low (2-5%) in the case of animals fed the FF-Fe diet. The proportion of 20:4 in total fatty acids of tissues was 2- to 3-fold greater in rats fed the FF-Fe diet than when they were fed the FF+Fe diet. Therefore, the relative levels of 20:3 omega 9/20:4 omega 6 varied from 1-2.9 in tissue lipids of rats fed the FF+Fe diet, while it varied only from 0.2-0.3 in animals fed the FF-Fe diet. These results suggest that a lack of dietary iron may reduce the synthesis of 16:1, 18:1, 20:3 and 20:4 and the metabolism of 20:4.

The positional specificity of a desaturase in the psychrophilic bacterium Micrococcus cryophilus (ATCC 15174)

The positional specificity of the desaturase activity in the psychrophilic bacterium Micrococcus cryophilus (ATCC 15174) is shown to be delta9. The desaturase is inhibited by sterculic acid. Small amounts of delta8, delta10 and delta11 isomers are present. The implications of these findings for fatty acid metabolism in M. cryophilus are discussed. It is suggested that the temperature-dependent chain length change, known to occur in the phospholipid fatty acids of this bacterium, is not mediated by either a temperature-dependent change in desaturase substrate specificity or the induction of new desaturase enzymes with novel positional specificity. It is concluded that the control by temperature of fatty acid chain length is mediated by either a temperature-dependent change in the products of fatty acid synthetase or a temperature-sensitive palmitate elongase.

Studies on the inhibition of the desaturases by cyclopropenoid fatty acids

Unwashed rat liver microsomes were used to study the inhibition of the delta6 and delta9 desaturases by cyclopropenoid fatty acids with the ring structure about the 9,10 or 6,7 carbon atoms. The 9,10 cyclopropenoid acid (sterculic acid) is shown to be an effective inhibitor of only delta9 desaturase and then only in the presence of MgCl2 and coenzyme A (presumably due to the formation of sterculoyl-CoA). Two 6,7 cyclopropenoid acids of different chain lengths showed no marked inhibition of either the delta6 or delta9 desaturase. By the use of [3H]-sterculic acid, it has been shown that under conditions of high inhibition of the delta9 desaturase the inhibitor is not covalently attached to the enzyme at any point. This disproves older ideas on the mechanism of inhibition that assumed reaction between the cyclopropenoid ring and sulphydryl groups on the enzymes.