Characterization of a sialyl alpha 2-3 transferase and a sialyl alpha 2-6 transferase from human platelets occurring in the sialylation of the N-glycosylproteins

Two sialyltransferases (EC 2.4.99.-) are extracted with Triton X-100 from human platelets and characterized with asialo 3H-labelled alpha 1-acid glycoprotein, an N-glycosylprotein. Methylation analysis of their specificities indicates that the enzymes transfer selectively sialic acid in a 3 or 6 position to oligosaccharides possessing Gal(beta 1-4)GlcNAc structure. The sialyl alpha 2-3 transferase was separated from the sialyl alpha 2-6 transferase by Ultrogel AcA34 column chromatography. Through affinity chromatography on CDPethanolamine-Sepharose, the two sialyltransferases are partly purified (5- and 20-fold enrichment of their specific activity, respectively, for sialyl alpha 2-3 transferase and alpha 2-6 transferase) and appear to be structurally heterogeneous.     

Role of a membranous sialyltransferase complex in the synthesis of surface polymers containing polysialic acid in Escherichia coli. Temperature-induced alteration in the assembly process.

Membrane-associated sialyltransferase complexes of Escherichia coli K-235 catalyze the synthesis of sialyl polymers which remain associated with the cell envelope. Sialyl monophosphorylundecaprenol is an intermediate in the formation of these unique surface structures, and fluidity of the lipid phase is required for the proper function of the enzyme complex (Troy, F.A., Vijay, I.K., and Tesche, N. (1975) J. Biol. Chem. 250, 156-163, 164-170). In membranes containing an increased unsaturated fatty acid content of the phospholipids, obtained by growing cells at 15 degrees C, synthesis of polysialic acid was uncoupled from synthesis of the sialyl lipid-linked intermediate. Using reconstruction experiments, the importance of the role of an endogenous acceptor in polymer formation was suggested by the unexpected finding that polysialic acid synthesis could be reactivated in inactive membranes by the addition of an exogenous acceptor which contained sialic acid. Concomitant with polymer synthesis was a rapid loss of labeled sialic acid from the lipid phase. The activated sialic acid was shown to be transferred directly to the exogenous acceptor. These results establish: 1) that the temperature-induced alteration in polymer synthesis resulted from the inability of cells grown at 15 degrees C to either synthesize or assemble a functional endogenous acceptor and not from a defect in the synthesis of the sialyltransferase; 2) the intermediate precursor role of lipid-soluble sialic acid in sialyl polymer synthesis; and 3) that the exogenous acceptor served directly as an "acceptor" and not as a catalytic "effector" which stimulated an inactive membrane-enzyme complex. These results are in accord with the possibility that the low temperature-induced derangement in polymer formation is a consequence of the altered lipid structure resulting from the greater unsaturated fatty acid content in the membrane phospholipids. U-14C-labeled exogenous acceptor was isolated from the culture filtrate of cells grown at 37 degrees C and purified to homogeneity by preparative polyacrylamide gel electrophoresis. The pure acceptor was characterized structurally as a homopolymer of sialic acid with a degree of polymerization of approximately 12. Potassium borohydride reduction of the acceptor prior to complete hydrolysis with neuraminidase established that the polymer possessed a free reducing terminus of sialic acid. Subsequent structural studies showed that these oligomers of sialic acid appeared in the culture filtrate as a result of acid-catalyzed hydrolysis from membrane-associated polysialic acids of about 150 to 200 sialyl residues. Marked diminution of several membrane proteins was observed for cells grown at 15 degrees C. The possible relationship of these alterations to the upward shift in unsaturated lipids and to the loss of a functional endogenous acceptor is currently under study.     

Modification of Sindbis Virus Glycoprotein by Host-Specified Glycosyl Transferases

The amino acid sequence of the membrane glycoprotein of Sindbis virus is specified by the viral genome, but it has not been determined whether the carbohydrate portion of this molecule is specified by the cell or by the virus. We have examined two of the enzyme activities which catalyze transfer of monosaccharides to glycoprotein (sialyl and fucosyl transferases). Comparison of particulate enzyme preparations from infected and uninfected cells showed no difference in either the specific activity or acceptor specificity of these enzymes. This is impressive in view of the fact that the Sindbis membrane glycoprotein is the only glycoprotein synthesized in the infected cell. It was also determined that sialyl transferase from uninfected cells is capable of transferring ((3)H) sialic acid to acceptor prepared from Sindbis membrane glycoprotein. These results imply that at least some of the carbohydrate of the virus glycoprotein can arise by host modification.     

D-aspartate oxidase in mammalian brain and choroid plexus

Abstract— Synaptosomes from guinea-pig cerebral cortex contain a fetuin: sialyl glyco-protein: glycosyl transferase; evidence is presented which indicates that both a sialyl transferase; evidence is presented which indicates that both a sialyl transferase and endogenous acceptors were located in the synaptosome ‘ghost’ fractions. Following solubilization of synaptosomes with Triton X-100 and the use of fetuin minus NANA as acceptor, 25 per cent of the transferase was recovered after centrifugation and column chromatography on Sephadex G-100 and G-200 with a 64·0-fold purification. The enzyme had a pH optimum of 6·3, required no divalent metal cation for activity, and exhibited high activity with either fetuin minus sialic acid, prothrombin minus sialic acid, Tamm-Horsfall glycoprotein minus sialic acid, or orosomucoid minus sialic acid as acceptor; neither BSM nor PSM minus NANA functioned as an effective acceptor. The fetuin:sialyl transferase using fetuin minus sialic acid and CMP-sialic acid as substrates a and b, respectively, gave the following kinetic constants when using the Cleland bisubstrate model: K_a= 35μM; K_b= 3 μM; K_ia, = 25 μM; K_ib= 25μM; and V₁= 92 pmoles. min^?1.mg^?1 of protein. The following divalent cations inhibited the reaction: Ba²⁺ > Hg²⁺ > Pb²⁺ > Cu²⁺.     

Dietary conjugated linoleic acid alters long chain polyunsaturated fatty acid metabolism in brain and liver of neonatal pigs

Effects of dietary conjugated linoleic acid (CLA, 1% mixed isomers) on n-6 long-chain polyunsaturated fatty acid (LCPUFA) oxidation and biosynthesis were investigated in liver and brain tissues of neonatal piglets. Fatty acid β-oxidation was measured in tissue homogenates using [1-¹⁴C]linoleic acid (LA) and -arachidonic acid (ARA) substrates, while fatty acid desaturation and elongation were traced using [U-¹³C]LA and GC-MS. Dietary CLA had no effect on fatty acid β-oxidation, but significantly decreased n-6 LCPUFA biosynthesis by inhibition of LA elongation and desaturation. Differences were noted between our ¹³C tracer assessment of desaturation/elongation and simple precursor-product indices computed from fatty acid composition data, indicating that caution should be exercised when employing the later. The inhibitory effects of CLA on elongation/desaturation were more pronounced in pigs fed a low fat diet (3% fat) than a high fat diet (25% fat). Direct elongation of linoleic acid to C20:2n-6 via the alternate elongation pathway might play an important role in n-6 LCPUFA synthesis because more than 40% of the synthetic products of [U-¹³C]LA accumulated in [¹³C]20:2n-6. Overall, the data show that dietary CLA shifted the distribution of the synthetic products of [U-¹³C]LA between elongation and desaturation in liver and decreased the total synthetic products of [U-¹³C]LA in brain by inhibiting LA elongation to C20:2n-6. The impact of CLA on brain LCPUFA metabolism of the developing neonate merits consideration and further investigation.     

Specificity of sialytransferase: structure of alpha1-acid glycoprotein sialylated in vitro. A new methodology for the determination of the structure of the linkage formed by glycosyltransferase action on galactosyl-oligosaccharide-protein acceptors.

The terminal galactosyl units of desialylated alpha1-acid glycoprotein were selectively labeled with tritium by a galactose oxidase/NaB3H4 procedure. The 3H-labeled glycoprotein was effective as an acceptor in sialytransferase reactions catalyzed by rat liver microsomes in vitro with unlabeled CMP-N-acetyl-neuramininic acid as sialic acid donor. Permethylation/hydrolysis of glycopeptides derived from the resialylated 3H-labeled glycoprotein yielded radioactive 2,3,4-trimethylgalactose indicating that rat liver microsomes are capable of transferring sialic acid to position C-6 of the terminal galactosyl units of desialylated alpha1-acid glycoprotein. No indication was obtained for transfer of sialic acid to other positions. This result is discussed in view of the multiplicity of positions of attachment of sialic acid to galactosyl residues in native alpha1-acid glycoprotein.     

Dietary alpha-linolenic acid suppresses the formation of lysophosphatidic acid,a lipid mediator,in rat platelets compared with linoleic acid

Rats fed a high linoleic acid (LA, 18:2n-6) diet or a high alpha-linolenic acid (ALA, 18:3n-3) diet for 4 months after weaning. Platelets from the high-LA group contained more arachidonic acid (AA, 20:4n-6) and less eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3) compared with those from the high-ALA group. Incorporation of [32P]orthophosphate into platelet phospholipids was increased by thrombin-treatment, and was greater by ca. 30% in the high-LA group than in the high-ALA group both in the presence and absence of thrombin. The formation of [32P]lysophosphatidic acid (LPA), a lipid messenger, in [32P]orthophosphate-labeled platelets was increased 6.6-fold in the high-LA group and 4.1-fold in the high-ALA-group by thrombin-treatment. The formation of [32P] LPA in activated platelets was reduced by 35% in the high-ALA group.     

Gamma-linolenic acid provides additional protection against ventricular fibrillation in aged rats fed linoleic acid rich diets

Ligation of the coronary artery in rats produces severe ventricular fibrillation (VF) and malignant cardiac arrhythmia. Mortality increases with the age of the animal. Diets rich in saturated fatty acids (SF) but low in linoleic acid (LA) increase, but diets high in LA and low in SF decrease the severity of VF and mortality in older animals. The effects of an LA enriched diet can be blocked by inhibition of cyclooxygenase suggesting that conversion of LA to eicosanoids is central to the development of VF. Conversion of LA to gamma-linolenic acid (GLA) via delta-6 desaturase is the first step in the process. The activity of delta-6 desaturase declines with age. Thus inclusion of GLA in the diet of older animals may provide an additional benefit over LA alone. Dietary supplements of evening primrose oil (EPO) to one year old rats reduced ischaemic VF more than a supplement of sunflower seed oil (SSO) without GLA. Substitution of borage oil (more GLA than EPO but less LA than either EPO or SSO) was without additional benefit.     

Comparison of hypolipidemic activity of synthetic gallic acid-linoleic acid ester with mixture of gallic acid and linoleic acid, gallic acid, and linoleic acid on high-fat diet induced obesity in C57BL/6 Cr Slc mice

Hyperlipidemia is the major risk factors of heart disease such as atherosclerosis, stroke, and death. In the present study, we studied the effect of gallic acid (GA), linoleic acid (LA), mixture of GA and LA (MGL), and chemically synthesized gallic acid-linoleic acid ester (octadeca-9,12-dienyl-3,4,5-trihydroxybenzoate, GLE) on the ability to ameliorate hyperlipidemia in C57BL/6 mice fed a high-fat diet (HFD). GLE, GA, LA, and MGL were mixed with HFD and the composition of the test compounds were 1% of the diet for 7 weeks. After 7 weeks, the average body weight of ND and GLE groups was lower than that of HFD group (P<0.05). The liver weight of mice decreased (P<0.05) in all treatment groups relative to HFD fed group. The plasma lipids such as triglyceride and LDL-cholesterol were found to be decreased (P<0.05) in GLE, GA, LA, and MGL fed mice when compared to that of HFD fed mice. But high-density lipoprotein (HDL) cholesterol increased (P<0.05) in HFD and GLE fed mice when compared to that of ND fed mice. The hepatic accumulation of fat droplets of GA, LA, GLE, and MGL group showed considerably lower than that of HFD group. Adipose histology showed that GLE supplementation was found to be more effective in decreasing the size of adipocyte relative to those of other treatment groups. In conclusion, the supplementation of synthetic GLE from gallic acid and linoleic acid ester may have a potential hypolipidemic effect on mice fed high-fat diet. Further studies are required to prove GLE as a hypolipidemic agent.     

Sialic acid metabolism's dual function in Haemophilus influenzae

Many bacterial commensals and pathogens use the sialic acids as carbon and nitrogen sources. In Escherichia coli, the breakdown of these sugars is catalysed by gene products of the nan (Nacylneuraminate) operon; other microorganisms may use a similar catabolic strategy. Despite the known ligand and antirecognition functions of the sialic acids, the contribution of their catabolism to infection or host colonization has never been directly investigated. We addressed these questions with Haemophilus influenzae type b, which metabolizes relatively few carbohydrates, using the infant-rat infection model. The predicted H. influenzae homologue (HI0142) of the E. coli sialic acid aldolase structural gene, nanA, was subcloned and mutagenized by insertion of a kanamycin resistance cassette. Phenotypic investigation of the resulting H. influenzae aldolase mutants showed that: (i) HI0142 is essential for sialic acid degradation; (ii) the products of the open reading frames (ORFs) flanking HI0142 (HI0140, 41, 44 and 45) are likely to have the same functions as those of their counterparts in E. coli; (iii) sialylation of the lipooligosaccharide (LOS) epitope recognized by monoclonal antibody 3F11 is dependent on an environmental source of sialic acid; (iv) a nanA mutant hypersialylates its LOS sialyl acceptor, corresponding to an apparent increased fitness of the mutant in the infant-rat model; and (v) expression of the LOS sialyl acceptor is altered in cells grown without exogenous sialic acid, indicating the direct or indirect effect of sialic acid metabolism on LOS antigenicity. Taken together the data show the dual role of sialic acid catabolism in nutrition and cell surface modulation.     

Reversible sialylation: synthesis of cytidine 5'-monophospho-N-acetylneuraminic acid from cytidine 5'-monophosphate with alpha2,3-sialyl O-glycan-, glycolipid-, and macromolecule-based donors yields diverse sialylated products

Sialyltransferases transfer sialic acid from cytidine 5'-monophospho-N-acetylneuraminic acid (CMP-NeuAc) to an acceptor molecule. Trans-sialidases of parasites transfer alpha2,3-linked sialic acid from one molecule to another without the involvement of CMP-NeuAc. Here we report another type of sialylation, termed reverse sialylation, catalyzed by mammalian sialyltransferase ST3Gal-II. This enzyme synthesizes CMP-NeuAc by transferring NeuAc from the NeuAcalpha2,3Galbeta1,3GalNAcalpha unit of O-glycans, 3-sialyl globo unit of glycolipids, and sialylated macromolecules to 5'-CMP. CMP-NeuAc produced in situ is utilized by the same enzyme to sialylate other O-glycans and by other sialyltransferases such as ST6Gal-I and ST6GalNAc-I, forming alpha2,6-sialylated compounds. ST3Gal-II also catalyzed the conversion of 5'-uridine monophosphate (UMP) to UMP-NeuAc, which was found to be an inactive sialyl donor. Reverse sialylation proceeded without the need for free sialic acid, divalent metal ions, or energy. Direct sialylation with CMP-NeuAc as well as the formation of CMP-NeuAc from 5'-CMP had a wide optimum range (pH 5.2-7.2 and 4.8-6.4, respectively), whereas the entire reaction comprising in situ production of CMP-NeuAc and sialylation of acceptor had a sharp optimum at pH 5.6 (activity level 50% at pH 5.2 and 6.8, 25% at pH 4.8 and 7.2). Several properties distinguish forward/conventional versus reverse sialylation: (i) sodium citrate inhibited forward sialylation but not reverse sialylation; (ii) 5'-CDP, a potent forward sialyltransferase inhibitor, did not inhibit the conversion of 5'-CMP to CMP-NeuAc; and (iii) the mucin core 2 compound 3-O-sulfoGalbeta1,4GlcNAcbeta1,6(Galbeta1,3)GalNAcalpha-O-benzyl, an efficient acceptor for ST3Gal-II, inhibited the conversion of 5'-CMP to CMP-NeuAc. A significant level of reverse sialylation activity is noted in human prostate cancer cell lines LNCaP and PC3. Overall, the study demonstrates that the sialyltransferase reaction is readily reversible in the case of ST3Gal-II and can be exploited for the enzymatic synthesis of diverse sialyl products.     

Cell-adhered conjugated linoleic acid regulates isomerization of linoleic acid by resting cells of Propionibacterium freudenreichii

The microbiological isomerization of linoleic acid (LA) to conjugated linoleic acid (CLA) was studied in resting cell suspensions of a propionibacterium and micellar LA to identify factors critical in the isomerization efficiency. These suspensions, containing cells 5x10(10) colony-forming units ml(-1) and 510 micro g LA ml(-1), isomerized about 90% of LA to CLA. However, the yield was not improved with higher amounts of micellar LA, suggesting that the cells had a fixed capacity to carry out the isomerization. This was explained by the fact that the CLA formed had a tendency to accumulate in the cell mass rather than in the aqueous micellar phase during the isomerization. Concomitantly, cell viability and isomerization rates were gradually reduced. Upon cessation of the reaction, about 46% of all the CLA formed was in the cell material. This accumulation to the cells was prevented by adding the detergent in excess to that required for micellization of LA. Then the cells remained viable, but the rate of isomerization was drastically lowered, due to impaired availability of LA from the fortified micellar phase to the cells. It was concluded that the phase distribution of substrate and product plays a critical role in the microbiological production of CLA.     

An extraordinary degree of structural specificity is required in neural phospholipids for optimal brain function: n-6 docosapentaenoic acid substitution for docosahexaenoic acid leads to a loss in spatial task performance

This study was conducted to determine whether provision of preformed dietary docosapentaenoic acid (DPAn-6) can replace docosahexaenoic acid (DHA) for brain function as assessed by spatial task performance. A newly modified artificial rearing method was employed to generate n-3 fatty acid-deficient rats. Newborn pups were separated from their mothers at 2 days of age and given artificial rat milk containing linoleic acid (LA), or LA supplemented with 1% DHA (DHA), 1% DPAn-6 (DPA) or 1% DHA plus 0.4% DPAn-6 (DHA/DPA). The animals were then weaned onto similar pelleted diets. At adulthood, behavioural tasks were administered and then the brains were collected for fatty acid analysis. The LA and DPA groups showed a lower (63-65%) brain DHA than the dam-reared, DHA and DHA/DPA groups and this loss was largely compensated for by an increase in brain DPAn-6. The brain fatty acid composition in the DPA group was the same as that in the LA group at adulthood. In the Morris water maze, the LA and DPA groups exhibited a longer escape latency than the dam-reared and DHA groups and had a defect in spatial retention. In conclusion, DPAn-6 could not replace DHA for brain function, indicating a highly specific structural requirement for DHA.     

A new strain of Butyrivibrio fibrisolvens that has high ability to isomerize linoleic acid to conjugated linoleic acid

A new strain of Butyrivibrio fibrisolvens (TH1) that has high potential to produce conjugated linoleic acid (CLA) was isolated. Strain TH1 had higher LA isomerase (LA-I) activity, and was much more tolerant to linoleic acid (LA) than other strains examined. However, high CLA reductase (CLA-R) activity resulted in the temporary accumulation of CLA and subsequent conversion to trans-vaccenic acid (t-VA). When LA was added to growing TH1 cultures in a solution with dimethylsulfoxide (LA/DMSO), CLA produced was greater than when LA was added in a mixture with bovine serum albumin (BSA). The number of viable cells decreased upon addition of LA/DMSO, but then increased as the CLA decreased upon its conversion to t-VA. This result suggests that B. fibrisolvens can resume growing by the removal of CLA from the cells. Most CLA was released from B. fibrisolvens cells by gentle washing with BSA, suggesting that CLA bound to the cells might be removed in the rumen and large intestine. Thus, CLA production by B. fibrisolvens in the digestive tract could be increased by a reduction in CLA-R activity without accompanying an overall decrease in the cell number of B. fibrisolvens. Fatty acids (FAs) with 18 carbon backbone inducted LA-I activity, whereas unsaturated FAs induced CLA-R activity, suggesting that FAs stimulate the synthesis of LA-I and CLA-R. Providing a diet with a low ratio of unsaturated to saturated FAs may favor CLA production.     

A protein-sialyl polymer complex involved in colominic acid biosynthesis. Effect of tunicamycin.

A protein-NeuAc complex involved in colominic acid biosynthesis has been identified in membrane preparations of Escherichia coli K-235. This compound had an Mr (estimated by SDS/polyacrylamide-gel electrophoresis and autoradiography) of about 100,000 and played the role of an 'initiator' or 'primer' (endogenous acceptor) in the synthesis of the whole polymer. Incubations of E. coli membranes with CMP-[14C]NeuAc (CMP-N-[14C]acetylneuraminic acid) pointed to the existence of a protein fraction (primer acceptor) that linked residues of sialic acid (N-acetylneuraminic acid, NeuAc) up to a maximal size, later releasing them as low-Mr sialyl polymers (LMrS, Mr less than 10,000). In the presence of colominic acid (final acceptor) the radioactivity linked to the protein quickly decreased, appearing stoichiometrically bound to the whole polysaccharide. When membrane preparations were previously digested with Streptomyces proteinase or de-activated by heating (80 degrees C, 10 min), no incorporation of labelled NeuAc into trichloroacetic acid-insoluble material was detected. These results suggested that colominic acid molecules are synthesized while they are bound to a proteinaceous acceptor that is subsequently excised in the presence of colominic acid, generating the native protein. The antibiotic tunicamycin inhibited the biosynthesis of colominic acid, affecting the synthesis of this protein-(NeuAc)n intermediate. All these results are described here for the first time.     

Properties and regional distribution of cerebral CMP-N-acetylneuraminic acid: Glycoprotein sialyltransferase

Glycoprotein sialyltransferase was studied in the rat brain and in the frontal grey cortex and corpus callosum of the calf brain. Activities were measured with endogenous acceptors as well as with desialized α₁-acid glycoprotein as an exogenous acceptor. The enzyme was characterized by means of its pH optimum, K_m values and requirements for detergent and cations. The properties of the rat and calf brain enzymes appeared to be very similar. Substrate specificity studies indicate that more than one glycoprotein sialyltransferase reaction may occur in brain. The regional distribution of the enzyme in the calf brain was rather uniform. From this it was concluded that glycoprotein sialyltransferase, at least for the greater part, is localized in membranes other than those of the synaptic complexes, and occurs in both neurons and glia cells. The regional distribution of the amounts of endogenous glycoprotein acceptor sites, which could be calculated from the sialyltransferase activities, showed a striking correlation with that of the protein-bound sialic acid, but not with the sialyltransferase activity. The role of these endogenous glycoprotein acceptors in cerebral sialoglycoprotein biosynthesis is discussed.     

Gastrocnemius Muscle Lipids in Relation to Diet in Two Mouse Mutants, 129Re-dy and A2G-adr, with Abnormal Muscle Function

The lipids of gastrocnemius muscle from normal and dystrophic (dy) mice of the Bar Harbor, 129Re strain were studied. Animals were fed diets containing either 3.1% or 1.1% of total calories as linoleic acid. Lipid analyses were also done on muscle from a new mouse mutant, A2G-adr, which has abnormal muscle function, characterised by an arrested development of the righting response. These animals were fed the "high" linoleic acid diet only. Total lipid, triacylglycerol, and cholesterol were elevated in the 129Re-dy irrespective of the diet, whereas A2G-adr possessed significantly higher levels of cholesterol. Total phosphorus (micrograms P/g muscle) and cholesterol/phospholipid ratios were elevated in the dy strains only. Cardiolipin was raised in the dy ("low" linoleic diet) and adr muscle, whereas phosphatidylcholine was lower in the adr strain only. Linoleic acid esterified to phosphatidylcholine, phosphatidylethanolamine, and phosphatidylserine was elevated whereas arachidonic acid in phosphatidylserine was decreased in both mutants. Docosahexanoic acid (22:6) in all three dy phospholipids was decreased, independent of dietary treatment. The adr strain possessed normal levels of this fatty acid. The results specifically point to an abnormality in long-chain polyunsaturated fatty acid metabolism in gastrocnemius muscle in the 129Re-dy mutant; in the adr mutant they could reflect an abnormal increase in the number of muscle mitochondria.     

Dietary linoleic acid is required for development of experimentally induced alcoholic liver injury

We had previously hypothesized that linoleic acid (LA) was essential for development of alcoholic induced liver injury in our rat model. Male Wistar rats were fed a nutritionally adequate diet (25% calories as fat) with ethanol (8-17 g/kg/day). The source of fat was tallow (0.7% LA), lard (2.5% LA) or tallow supplemented with linoleic acid (2.5%). Liver damage was followed monthly by obtaining blood for alanine aminotransferase assay and liver biopsy for assessment of morphologic changes. Enzyme and histologic changes (fatty liver, necrosis and inflammation) in the tallow-linoleic acid-ethanol fed animals were more severe than in the lard-ethanol group. The tallow ethanol group did not show any evidence of liver injury. Our results strongly support our hypothesis that LA is essential for development of alcoholic liver disease in our rat model.     

Dietary omega-6 fatty acid lowering increases bioavailability of omega-3 polyunsaturated fatty acids in human plasma lipid pools

BackgroundDietary linoleic acid (LA, 18:2n-6) lowering in rats reduces n-6 polyunsaturated fatty acid (PUFA) plasma concentrations and increases n-3 PUFA (eicosapentaenoic (EPA) and docosahexaenoic acid (DHA)) concentrations.ObjectiveTo evaluate the extent to which 12 weeks of dietary n-6 PUFA lowering, with or without increased dietary n-3 PUFAs, alters unesterified and esterified plasma n-6 and n-3 PUFA concentrations in subjects with chronic headache.DesignSecondary analysis of a randomized trial. Subjects with chronic headache were randomized for 12 weeks to (1) average n-3, low n-6 (L6) diet; or (2) high n-3, low n-6 LA (H3–L6) diet. Esterified and unesterified plasma fatty acids were quantified at baseline (0 weeks) and after 12 weeks on a diet.ResultsCompared to baseline, the L6 diet reduced esterified plasma LA and increased esterified n-3 PUFA concentrations (nmol/ml), but did not significantly change plasma arachidonic acid (AA, 20:4n-6) concentration. In addition, unesterified EPA concentration was increased significantly among unesterified fatty acids. The H3–L6 diet decreased esterified LA and AA concentrations, and produced more marked increases in esterified and unesterified n-3 PUFA concentrations.ConclusionDietary n-6 PUFA lowering for 12 weeks significantly reduces LA and increases n-3 PUFA concentrations in plasma, without altering plasma AA concentration. A concurrent increase in dietary n-3 PUFAs for 12 weeks further increases n-3 PUFA plasma concentrations and reduces AA.     

Impact of linoleic acid intake on arachidonic acid formation and eicosanoid biosynthesis in humans

Long-chain conversion of linoleic acid (LA) and eicosanoid formation was followed in 6 healthy females who were given for 6 weeks liquid formula diets which contained no arachidonic acid but, for 2 weeks each, a LA supply of 0 energy% (en%), 4 en%, and 20 en%, respectively. RESULTS: higher LA intake resulted in higher LA percentages in investigated lipids, but not in higher amounts of LA present in plasma cholesterol esters or phosphatidylcholine of LDL and HDL comparing liquid formula diet (LFD) 4 and LFD 20. A higher intake of LA resulted in a decrease of arachidonic acid, which was most prominent in HDL phosphatidycholine. Eicosanoids derived from cyclo-oxygenase activity were unchanged by LA intake, while an increase of cytochrome P450-dependent tetranorprostanedioic acid formation was observed with LFD 20. CONCLUSION: LA intake of 4 en% appears to be a recommendable intake, without signs of stimulated eicosanoid biosynthesis or oxidation.