Incorporation of radioactive polyunsaturated fatty acids into liver and brain of developing rat

The incorporation of radioactivity from orally administered linoleic acid-1-¹⁴C, linolenic acid-1-¹⁴C, arachidonic acid-³Hg, and docosahexaenoic acid-¹⁴C into the liver and brain lipids of suckling rats was studied. In both tissues, 22 hr after dosing, 2 distinct levels of incorporation were observed: a low uptake (from 18∶2-1-¹⁴C and 18∶3-1-¹⁴C) and a high uptake (from 20∶4-³H₈ and 22∶6-¹⁴C). In adult rats, the incorporation of radioactivity into brain lipids from 18∶2-1-¹⁴C and 20∶4-³H was considerably lower than the incorporation into the brains of the young rats. In the livers of the suckling rats, the activity from the 18 carbon acids was associated mostly with the triglyceride fraction, whereas the activity from the 20∶4-³H₈ and 22∶6-¹⁴C was concentrated in the phospholipid fraction. In the brain lipids, the activity from the different fatty acids was associated predominantly with the phospholipids. In the liver and brain phospholipid fatty acids, some of the activity in the 18∶2-1-¹⁴C and 18∶3-1-¹⁴C experiments was associated with 20 and 22 carbon polyunsaturated fatty acids; however, radioactivity from orally administered 20∶4-³H₈ and 22∶6-¹⁴C was incorporated intact into the tissue phospholipid to a much greater extent compared with the incorporation of radioactivity into 20∶4 and 22∶6 in the experiments where 18∶2-1-¹⁴C and 18∶3-1-¹⁴C, respectively, were administered. Possible reasons for these differences are discussed. Rat milk contains a wide spectrum of polyunsaturated fatty acids, including linoleate, linolenate, arachidonate, and docosahexaenoate. During the suckling period in the rat, there is a rapid deposition of 20∶4 and 22∶6 in the brain. The results of the present experiments suggested that dietary 20∶4 and 22∶6 were important sources of brain 20∶4 and 22∶6 in the developing rat.     

Enzymatic modification of trilinolein: Incorporation of n-3 polyunsaturated fatty acids

Two immobilized lipases, IM60 fromMucor miehei and SP435 fromCandida antarctica, were used as biocatalysts for the modification of trilinolein with n-3 polyunsaturated fatty acids (PUFA), such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), by using their ethyl esters as acyl donors (EEPA and EDHA, respectively). Transesterification (ester-ester interchange) reactions were carried out in organic solvent. The products were analyzed according to their equivalent carbon number and polarity by reverse-phase high-performance liquid chromatography, and the fatty acid profiles were determined by gas-liquid chromatography. Modified triacylglycerol products contained 1 or 2 molecules of n-3 PUFA. With EEPA as the acyl donor, the total EPA product yields with IM60 and SP435 as biocatalysts were 79.6 and 81.4%, respectively. However, with EDHA as the acyl donor and IM60 and SP435 as biocatalysts, the total DHA product yields were 70.5 and 79.7%, respectively. Effects of reaction parameters, such as type of solvent, enzyme load, time course, and molar ratio of substrates on the n-3 PUFA incorporation, were followed with SP435 as the biocatalyst. High yields were obtained, even in the absence of organic solvent. These lipids do hold promise for specialty nutrition and other therapeutic uses.     

Incorporation of 1-14C-Acetate into C26 fatty acids of the marine spongeMicrociona prolifera

The incorporation of 1-¹⁴C-acetate into the many fatty acids of the marine spongeMicrociona prolifera was investigated. Probable precursors of 26∶2Δ5,9 and 26∶3Δ5,9,19 showed high levels of radioactivity, supporting the following pathways for the biosynthesis of C₂₆ acids: $$\begin{array}{*{20}c} {16:0 \to \to \to 26:0 \to 26:1\Delta 9 \to 26:2\Delta 5,9} \\ {16:1\Delta 9 \to \to \to 26:1\Delta 19 \to } \\ {26:2\Delta 9,19 \to 26:3\Delta 5,9,19} \\ \end{array}$$ Degradation of the unsaturated C₂₆ acids at their double bonds showed that the¹⁴C was concentrated near the carboxyl end of the chain. Hence, chain elongation was the major mechanism for acetate incorporation into these acids.     

Incorporation oftrans fatty acids into submandibular salivary gland lipids

Three groups of rats were fed diets containing 20% corn oil, 20% margarine stock (MS) or 19% MS +1% corn oil. Diets were fed for 12 weeks, 1 week of pregnancy, 3 weeks of lactation and 8 weeks post-weaning. The incorporation oftrans-octadecenoate into various lipids of the submandibular salivary gland (SMSG) homogenates and plasma membranes was studied.Trans octadecenoate was incorporated into all the lipid fractions studied. Its levels were the highest in phosphatidylethanolamine. The double bond index of phospholipid fatty acids in the plasma membranes of the SMSG was substantially lower in the group fed 20% MS. The fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH) was generally higher in the membranes of SMSG from rats fed MS than that of the other two groups, thus indicating lower fluidity. Also, the breakpoints in fluorescence polarization were at a higher temperature in the membranes from rats fed MS as compared with those fed corn oil. Lower fluidity of plasma membranes of SMSG observed in rats fed 20% MS may result in modification of the activities of membrane-bound enzymes. Part of this work was presented at the Federation of American Societies for Experimental Biology (FASEB) 68th Annual Meeting, St. Louis, Missouri, April 1984. Alam, S.Q., Alam, B.S., and Banerji, A. Fed. proc. 43,317 (1984).     

Enzymatic modification of evening primrose oil: Incorporation of n−3 polyunsaturated fatty acids

Immobilized lipase SP435 fromCandida antaractica was used as a biocatalyst for the modification of the fatty acid composition of evening primrose oil by incorporating n−3 polyunsaturated fatty acid (PUFA) and eicosapentaenoic acid (EPA). Transesterification (ester-ester interchange) was conducted in organic solvent or without solvent, with EPA ethyl ester (EEPA) as the acyl donor. Products were analyzed by gas-liquid chromatography (GLC). After 24-h incubation in hexane, the fatty acid composition of evening primrose oil was markedly changed to contain up to 43% EPA. The amount of 18:2n−6 PUFA was reduced by 32%, and the saturated fatty acid content was also reduced. The effects of incubation time, molar ratio, enzyme load, and reaction medium on mol% EPA incorporation were also studied. Generally, as the incubation time (up to 24 h), molar ratio, and enzyme load increased, EPA incorporation also increased. Evening primrose oil, containing EPA and γ-linolenic acid (18:3n−6) in the same glycerol backbone, was successfully produced and may be more beneficial for certain applications than unmodified oil.     

Incorporation oftrans long-chain n−3 polyunsaturated fatty acids in rat brain structures and retina

During heat treatment, polyunsaturated fatty acids and specifically 18∶3n−3 can undergo geometrical isomerization. In rat tissues, 18∶3 Δ9c, 12c, 15t, one of thetrans isomers of linolenic acid, can be desaturated and elongated to givetrans isomers of eicosapentaenoic and docosahexaenoic acids. The present study was undertaken to determine whether such compounds are incorporated into brain structures that are rich in n−3 long-chain polyunsaturated fatty acids. Two fractions enriched intrans isomers of α-linolenic acid were prepared and fed to female adult rats during gestation and lactation. The pups were killed at weaning. Synaptosomes, brain microvessees and retina were shown to contain the highest levels (about 0.5% of total fatty acids) of thetrans isomer of docosahexaenoic acid (22∶6 Δ4c, 7c, 10c, 13c, 16c, 19t). This compound was also observed in myelin and sciatic nerve, but to a lesser extent (0.1% of total fatty acids). However, the ratios of 22∶6trans to 22∶6cis were similar in all the tissues studied. When the diet was deficient in α-linolenic acid, the incorporation oftrans isomers was apparently doubled. However, comparison of the ratios oftrans 18∶3n−3 tocis 18∶3n−3 in the diet revealed that thecis n−3 fatty acids were more easily desaturated and elongated to 22∶6n−3 than the correspondingtrans n−3 fatty acids. An increase in 22∶5n−6 was thus observed, as has previously been described in n−3 fatty acid deficiency. These results encourage further studies to determine whether or not incorporations of suchtrans isomers into tissues may have physiological implications. Presented in part at the 32nd International Conference on the Biochemistry of Lipids, 1991, Granada, Spain. Delta nomenclature (Δ) is used fortrans polyunsaturated fatty acids to specify the position and geometry of ethylenic bonds. Polyunsaturated fatty acids containingtrans double bonds are abbreviated giving the locations of thetrans double bonds only; e.g., 20∶5 Δ17t 20∶5 Δ5c,8c,11c,14c,17t; 22∶5 Δ19t, 22∶5 Δ7c,10c,13c,16c,19t; 22∶6 Δ19t 22∶6 Δ4c,7c,10c,13c,16c,19t.     

Lipase-catalyzed incorporation of n−3 polyunsaturated fatty acids into vegetable oils

The ability of immobilized lipases IM60 fromMucor miehei and SP435 fromCandida antarctica to modify the fatty acid composition of selected vegetable oils by incorporation of n−3 polyunsaturated fatty acids into the vegetable oils was studied. The transesterification was carried out in organic solvent with free acid and ethyl esters of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) as acyl donors. With free EPA as acyl donor, IM60 gave higher incorporation of EPA than SP435. However, when ethyl esters of EPA and DHA were the acyl donors, SP435 gave higher incorporation of EPA and DHA than IM60. When IM60 and free acid were used, the addition of 5 μL water increased EPA incorporation into soybean oil by 4.9%. With ethyl ester of EPA as acyl donor, addition of 2 μL water increased EPA incorporation by 3.9%. For SP435, addition of water up to 2μL resulted in increased EPA incorporation, but the incorporation declined when the added water exceeded this amount. The addition of water increased the EPA incorporation into Trisun 90 after 24 h reaction but not the reaction rate at early stages of the reaction.     

Incorporation of fatty acids into phospholipids in L cells stimulated by antibody

Binding antibodies to surface membranes stimulated incorporation of fatty acids (FA) into phospholipids of L cells. Antibodies stimulated at least a 3.4-fold greater incorporation of arachidonic acid into phosphatidylinositol than into any other class of phospholipid when compared on a molar basis (p<0.003). This enhanced incorpoation was selective, depending on the character of the FA, because antibodies stimulated the incorporation of arachidonic acid at least 2.4-fold more than oleic acid, palmitic acid or stearic acid (p<0.001). Surprisingly, an antibody-stimulated incorporation of palmitic acid into sphingomyelin (SM) was at least 2.2-fold greater than that into any other class of phospholipid (p<0.001) and the antibody-stimulated incorporation of palmitic acid into SM was at least 60-fold greater than that of arachidonic acid, stearic or oleic acid (p<0.001). Nontoxic doses of ethylenediamine tetraacetic acid (EDTA), dexamethasone, 4-bromophenacylbromide and indomethacin inhibited the antibody-stimulated incorporation of arachidonic acid into cellular phospholipids, principally phosphatidylinositol (PI), and similarly inhibited the antibody stimulation of DNA synthesis. We conclude that when antibody binds to surface antigens on L cells, a rapid and selective incorporation of fatty acids into certain cellular phospholipids occurs, possibly mediated by calcium-dependent phospholipases. Degradation products of arachidonic acid, i.e., prostaglandins, may be important in these antibody stimulation events, as well. These early changes in phospholipid metabolism may serve as an important signal or mechanism for the subsequent stimulation of DNA synthesis in L cells.     

Industrial chemical uses of polyunsaturated fatty acids

Production of vegetable, animal and marine oils containing more than about 40% unsaturated fatty acids totaled 15,000 million pounds in 1968, almost on the scale of petrochemical production. The greater share (64%) of this nonfossil oil production was directed toward food uses, the remainder toward industrial and animal feed uses. The variety of chemical reactions carried out on these unsaturated fatty acid products include hydrogenation, interesterification, dimerization, sulfation, formation of nitrogen compounds, epoxidation, alkaline cleavage and oxidative ozonolysis. Some of these reactions have been developed at Utilization Research and Development Divisions of the Agricultural Research Service, U.S. Department of Agriculture. Research is continuing in developing new reactions for potential industrial application. An example is reductive ozonolysis of unsaturated fatty esters to produce monofunctional aldehydes and bifunctional aldehyde esters. Presented at the ISF-AOCS World Congress, Chicago, September 1970. No. Market. Nutr. Res. Div., ARS, USDA.     

Lipase-catalyzed enrichment of long-chain polyunsaturated fatty acids

Lipase hydrolysis was evaluated as a means of selectively enriching long-chain ω3 fatty acids in fish oil. Several lipases were screened for their ability to enrich total ω-3 acids or selectively enrich either docosahexaenoic acid (DHA) or eicosapentaenoic acid (EPA). The effect of enzyme concentration, degree of hydrolysis, and fatty acid composition of the feed oil was studied. Because the materials that were enriched in long-chain ω3 acids were either partial glycerides or free fatty acids, enzymatic reesterification of these materials to triglycerides by lipase catalysis was also investigated. Hydrolysis of fish oil by eitherCandida rugosa orGeotrichum candidum lipases resulted in an increase in the content of total ω3 acids from about 30% in the feed oil to 45% in the partial glycerides. The lipase fromC. rugosa was effective in selectively enriching either DHA or EPA, resulting in a change of either the DHA/EPA ratio or the EPA/DHA ratio from approximately 1:1 to 5:1. Nonselective reesterification of free fatty acids or partial glycerides that contained ω3 fatty acids could be achieved at high efficiency (approximately 95% triglycerides in the product) by using immobilizedRhizomucor miehei lipase with continuous removal of water.     

Lipase-catalyzed modification of phospholipids: Incorporation of n-3 fatty acids into biosurfactants

Phospholipids were successfully modified by lipase-catalyzed transesterification to incorporate n-3 polyunsaturated fatty acids such as eicosapentaenoic acid (20:5) and docosahexaenoic acid (22:6). The phospholipid modification was carried out in organic media with lipase fromMucor miehei (lipozyme) as biocatalyst. The parameters studied were the effect of different solvents, enzymes, acyl donor type, phospholipid class, water, enzyme and substrate concentrations. Hydrolysis of phosphatidylcholine to yield lysophosphatidylcholine and the synthesis of phosphatidylcholine from lysophosphatidylcholine was also carried out. The optimal conditions for the modification of phospholipids by transesterification were obtained with phosphatidylcholine and free eicosapentaenoic acid EPA 45 as acyl donor in the presence of 15% w/w nonimmobilizedMucor miehei lipase (lipozyme) in hexane with no added water. The maximum incorporation of EPA 45 was 17.7 mol%. Hydrolysis was easily achieved with phospholipase A₂ in benzene and Tris-HCl buffer. The synthesis of phosphatidylcholine was difficult, and when it was achieved, not enough phosphatidylcholine was obtained for quantitation.     

The biosynthesis of polyunsaturated fatty acids in plants

This paper is a review of some of the work being done at the author's laboratory. The phospholipids and glycolipids of the alga,Chlorella vulgaris, have been implicated in fatty acid transformations such as chain elongation and desaturation. Labeling studies with [¹⁴C] acetate have shown that newly synthesized galactosyl glycerides have mainly saturated fatty acids. Subsequent to de novo synthesis, a series of alterations of fatty acid structure takes place within the same glycolipid molecules. The specific incorporation of [¹⁴C] oleic acid intoChlorella phosphatidyl choline provides a convenient model system for studying the lipid dependent desaturation of oleic to linoleic acid. The inhibitor of fatty acid desaturation, sterculic acid, only inhibits the conversion of oleate into linoleate if added before the precursor fatty acid has been incorporated into a complex lipid. Studies with isomeric monoenoic fatty acids have suggested that there are two enzymes which catalyze the formation of linoleic from oleic acid. One measures the position of the second double bond from the carboxyl group, the other, from the methyl end of the chain. The latter enzyme probably requires the complex lipid substrate.     

Effect of polyunsaturated fatty acids in obese mice

Genetically obese (ob/ob) mice display a variety of metabolic differences from lean litter mates. In the obese state, fatty acid desaturation-elongation in brown adipose tissue mitochondria is apparently altered, resulting in differences in membrane fatty acid composition. This change in membrane lipid environment appears to influence GDP binding and there-fore the activity of the proton conductance pathway associated with regulation of energy expenditure in these animals. In liver, binding of insulin to the nuclear membrane is increased by feeding a high polyunsaturated/saturated (P/S) diet fat. Consumption of a high P/S diet decreased mRNA levels for fatty acid synthase, acetyl-CoA carboxylase, malic enzyme, and pyruvate kinase in obese and lean animals. Expression of mRNA for these lipogenic enzymes was higher in obese animals and suggests that obese mice may be resistant to polyunsaturated fatty acid feedback control of gene expression.     

Effects of hyperoxia and diet on murine tissue levels of vitamin E and polyunsaturated fatty acids

One hundred eighty-six adult female mice were studied to examine the effect of manipulating dietary vitamin E and fractional inspired oxygen concentrations (FiO₂) on tissue levels of vitamin E, total polyunsaturated fatty acids (TPUFA) and conjugated dienes (CD) as an index of lipid peroxidation. Animals were fed custom diets containing either 0, 50 or 150 ppm DL-α-tocopheryl acetate. Once plasma vitamin E levels of mice fell below 0.2 mg/dl (at week 19), all mice were placed in chambers containing either room air (FiO₂≈0.21) or FiO₂>0.95 for the next 72 hr. Dietary manipulation had a major impact on the levels of vitamin E in plasma, lung and perirenal adipose tissues (p<0.0001, p<0.0001 and p<0.005, respectively). Dietary vitamin E deprivation was associated with significant reductions in lung glutathione peroxidase (GPX) activities (p<0.05) and in plasma TPUFA levels (p<0.05). No significant effect attributable to either diet or FiO₂ was observed for liver vitamin E, liver TPUFA or lung TPUFA levels, or for those of CD in any tissue examined. Adipose TPUFA levels were depressed in all dietary groups exposed to FiO₂>0.95, when compared with those of groups exposed to room air. The high FiO₂ exposures also were associated with marked reductions in lung to body weight ratios (p<0.01). These data suggest that dietary vitamin E treatment after long-term feeding can modify vitamin levels in plasma, lung and adipose tissue, and lung GPX activities. Vitamin E levels in liver seemed less responsive to our dietary manipulations in adult female mice, though expressing liver vitamin E levels in terms of TPUFA revealed significant differences between the ratios from 0 and 150 ppm vitamin E groups (p<0.05).     

The metabolism ofTrans,trans-octadecadienoic acid. Incorporation ofTrans,trans-octadecadienoic acid into the C20 polyunsaturated acids of the rat

Trans,trans-9,12-octadecadienoic acid-1-C¹⁴ was fed to adult rats. After four hr the animals were killed and the fatty acids isolated from their organ lipids. The 20-carbon fatty acids were isolated and degraded stepwise. Radioactivity of the degradation products indicated that the fed acid was incorporated into the isolated C₂₀ acids, mainly eicosatetraenoic acid probably with twotrans-double bonds, while radio-activity throughout the chain gave evidence for a synthesis of eicosatrienoic and eicosatetraenoic acid from acetate derived from the fed material. In a separate experiment, unlabeledtrans,trans-9,12-octadecadienoic acid was fed to wealing rats for 14 days. Isolation of their fatty acids also gave evidence for the incorporation of the fed acid into eicosatrienoic and eicosatetraenoic acids containingtrans double bonds. Supported in part by Contract AT(04-1)GEN-12 between Atomic Energy Commission and University of California, by lipid training grant USPHS TI HE-5306 and by a grant from the Nutrition Foundation. Supported in part by Public Health Service Research Career Award No. GM-K6-19, 177 from the Div. of General Medical Sciences, National Institutes of Health.     

Enrichment of polyunsaturated fatty acids withGeotrichum candidum lipase

Three lipases, isolated previously in our laboratory, each with different fatty acid and positional specificities, and a known lipase fromCandida cylindracea were screened for concentrating docosahexaenoic (DHA) and eicosapentaenoic (EPA) acids in glycerides.Geotrichum candidum lipase was found to be suitable for their concentration in glycerides. Tuna oil was treated at 30°C with this lipase for 16 h, and 33.5% hydrolysis resulted in the production of glycerides containing 48.7% of DHA and EPA. The hydrolysis was not increased despite adding further lipase, so the glycerides were extracted, and the reaction was repeated. The second hydrolysis produced glycerides containing 57.5% of DHA and EPA in a 54.5% yield, with recovery of 81.5% of initial DHA and EPA. Of the total glycerides, 85.5% were triglycerides. These results showed thatG. candidum lipase was effective in producing glycerides that contained a high concentration of polyunsaturated fatty acids in good yield.     

Incorporation of lipids labeled with various fatty acids into the cytoskeleton of aggregating platelets

Earlier studies showed that during the first 20 to 25 seconds of aggregation induced by thrombin (0.1 U/mL) or adenosine diphosphate (ADP) (2μM) of rabbit or human platelets prelabeled with [³H]palmitic acid, labeled lipid became associated with the cytoskeleton (isolated after lysis with 1% Triton X-100, 5 mM EGTA [ethylene glycol-bis-(β-aminoethyl ether(N,N,N′,N′-tetraacetic acid] in the presence of 0.5 mM leupeptin and 50 mM benzamidine). In comparison with labeled lipid in intact platelets, the labeled lipid that was associated with the cytoskeleton was enriched in phospholipids and ceramide. To determine whether these effects were specific for lipids labeled with palmitic acid, we studied rabbit platelets in which lipids had been labeled by incubation of the platelets with pairs of¹⁴C- or³H-labeled palmitic, stearic, arachidonic, and linoleic acids. Examination of the distribution of label among the lipid classes of intact platelets showed that phospholipids contained most of the label. Under the conditions of limited, thrombin-induced aggregation used, labeled lipids were not lost from the platelets and the distribution of label among the lipid classes was essentially unchanged. There were major differences in the incorporation of labeled lipids into the cytoskeleton. The greatest incorporation (2.1 to 2.8% of the label in the platelets) was observed with palmitic acid-labeled lipids; by direct comparison, only 44% as much of the label of stearic acid-labeled lipids, 21% as much of the label of linoleic acid-labeled lipids, and only 6% as much of the label of arachidonic acid-labeled lipids was incorporated into the cytoskeleton. Thus the pool of phospholipid that is readily labeled with arachidonic acid appears to be selectively excluded from the cytoskeleton. Also noteworthy is the 4- to 5-fold enrichment of the cytoskeleton with labeled ceramide; an average of 16% of the label from stearic acid in the cytoskeleton was in ceramide. We suggest that ceramide and phospholipids that are readily labeled with saturated fatty acids are selectively incorporated into the cytoskeleton during the early stages of aggregation and may be specifically associated with the points of contact between platelets.     

Influence of moderate amounts of trans fatty acids on the formation of polyunsaturated fatty acids

The effect of trans fatty acids from partially hydrogenated soybean oil and butterfat on the formation of polyunsaturated fatty acids was investigated. Five groups of rats were fed diets that contained 20 wt% fat. The content of linoleic acid was adjusted to 10 wt% of the dietary fats in all diets, whereas the amount of trans fatty acids from partially hydrogenated soybean oil (PHSBO) was varied from 4.5 to 15 wt% in three of the five diets. The fourth group received trans fatty acids from butterfat (BF), while the control group was fed palm oil without trans fatty acids. Trans fatty acids in the diet were portionally reflected in rat liver and heart phosphatidylethanolamine (PE), phosphatidylcholine (PC), phosphatidylinositol, and phosphatidylserine. Incorporation in the sn-1 position was compensated by a decrease in saturated fatty acids. Trans fatty acids were not detected in diphosphatidylglycerol. Compared to the presence in the dietary fats, 8t- and 10t-18:1 were discriminated against in the incorporation in PE and PC from liver and heart, whereas 9t- and 12t-18:1 were preferred. The formation of 20:4n-6 was not influenced by 4.5 wt% trans fatty acids (from PHSBO) but apparently was by 10 wt% in liver. In contrast, even a content of 2.5 wt% trans fatty acids from BF reduced the formation of 20:4n-6. The inhibitory effect of trans isomers on linoleic acid conversion was reflected less in heart than in liver and less for PE than for PC. Groups with trans fatty acids showed increased 22:6n-3 and 22:5n-3 deposition in liver and heart PE and PC.     

The intestinal mucosa as a target for dietary polyunsaturated fatty acids

Several studies have reported beneficial effects of dietary polyunsaturated fatty acids (PUFA) on various aspects of both human and animal health, and particular reference has been made to their effects on systemic immune responses. Both immune stimulation and immune suppression have been reported, with the outcome dependent on the type of PUFA, the target cell, as well as the immune competence of the cells before exposure. The systemic and the mucosal immune systems are discrete entities, which have evolved specific approaches in the defense of the host. The latter comprises several interconnected tissues, which communicate with one another through the action of soluble mediators and the trafficking of cellular components. After the oral mucosa, the intestinal epithelium and its associated gutassociated lymphoid tissue are the primary targets of dietary components. Absorption of dietary PUFA and its incorporation into intestinal tissues has been well studied, but the consequences of these events in relation to local immune responses have received little attention. This article describes some of the immune mechanisms operating at this barrier and, where possible, pinpoints areas for which a modulatory role for PUFA has already been demonstrated. Although not an exhaustive treatise of the subject, it is hoped that this review will foster research into the specific interaction between dietary PUFA and cell populations comprising the intestinal barrier.     

Enzymatic synthesis of steryl esters of polyunsaturated fatty acids

Steryl esters of long-chain fatty acids have water-holding properties, and polyunsaturated fatty acids (PUFA) have various physiological functions. Because steryl ester of PUFA can be expected to have both features, we attempted to synthesize steryl esters of PUFA by enzymatic methods. Among lipases used, Pseudomonas lipase was the most effective for the synthesis of cholesteryl docosahexaenoate. When a mixture of cholesterol/docosahexaenoic acid (3:1, mol/mol), 30% water, and 3000 units/g of lipase was stirred at 40°C for 24 h, the esterification extent attained 89.5%. Under the same reaction conditions, cholesterol, cholestanol, and sitosterol were also esterified efficiently with docosahexaenoic, eicosapentaenoic, arachidonic, and γ-linolenic acids.