Functional lipidomics of oxidized products from polyunsaturated fatty acids

Because of their high degree of unsaturation, polyunsaturated fatty acids (PUFA) in mammals, with mainly 18, 20 and 22 carbons, can easily be autooxidized, and converted into many oxidized derivatives and degradation products. This short review reports on some of those relevant to the evaluation of oxidative stress in situ. In addition, the enzyme-dependent oxygenation by both dioxygenases and monooxygenases is briefly reviewed by functional and/or metabolic categories, pointing out the structure variety and the analytical approaches.     

The effect of bio-converted polyunsaturated fatty acids on the oxidation of TAG containing highly unsaturated fatty acids

Microbial modification of vegetable fatty acids can often lead to special changes in their structure and in biological function. A bacterial strain, Pseudomonas aeruginosa PR3, is known to carry out multiple hydroxylations on polyunsaturated fatty acids containing 1,4-cis, cis diene structural units, resulting in antibacterial activity. In this paper, in an effort to understand the overall mechanism involved in the varied biological functions of the complicated metabolites of bio-converted polyunsaturated fatty acids, we performed bioconversion of several polyunsaturated fatty acids using PR3, and determined their oxidative activities against fish oil. Bio-converted linoleic acid, eicosapentanoic acid, and docosahexanoic acid promoted effectively oxidation of fish oil. It is assumed that this oxidative effect could plausibly play an important role in the antimicrobial function of these bio-converted fatty acids.     

Correlation between medium C-chain fatty acids and polyunsaturated fatty acids

The medium C-chain fatty acids increased in the muscle, lungs, pancreas and adipose tissue (and not in the liver) of the rats injected with CCl4 or nourished with "balanced" diet for the lipids. When CCl4 and balanced diet are furnished together, these acids decrease strongly: the discussion of the results is difficult.     

Effects of polyunsaturated fatty acids on hibernation and torpor: a review and hypothesis

Polyunsaturated fatty acids (PUFAs) can have strong effects on hibernation and daily torpor in mammals. High dietary PUFA contents were found to increase proneness for torpor, decrease body temperatures, prolong torpor bout duration, and attenuate hibernation mass loss. The mechanism by which PUFAs enhance torpor and hibernation is unknown, however. On the basis of a review of the literature, and on reexamining our own data on alpine marmots, we propose that effects on hibernation are not due to PUFAs in general, but to shifts in the ratio of n-6 PUFAs to n-3 PUFAs in membrane phospholipids. Specifically, high ratios of n-6 to n-3 PUFAs increase the activity of the Ca2+-Mg2+ pump in the sarcoplasmic reticulum of the heart (SERCA) and counteract Q10 effects on SERCA activity at low tissue temperatures. Therefore, high n-6 to n-3 PUFA ratios in cardiac myocyte membranes appear to protect the hibernating heart from arrhythmia, which in hypothermic nonhibernators is caused by massive increases in cytosolic Ca2+. The resulting reduced risk of cardiac arrest during hypothermia may explain why increased dietary uptake of n-6 PUFAs, but not of n-3 PUFAs, can strongly enhance the propensity for hibernation, and allows heterotherms to reach lower body temperatures, with associated increased energy savings. Therefore, at least for herbivorous hibernators, such as marmots, linoleic acid (C18:2 n-6)--the dietary source of all n-6 PUFAs--appears to represent a crucial and limited resource in natural environments.     

Odd-chain polyunsaturated fatty acids in thraustochytrids

A series of unusual odd-chain fatty acids (OC-FA) were identified in two thraustochytrid strains, TC 01 and TC 04, isolated from waters off the south east coast of Tasmania, Australia. FA compositions were determined by capillary GC and GC–MS, with confirmation of polyunsaturated fatty acids (PUFA) structure performed by analysis of 4,4-dimethyloxazoline derivatives. PUFA constituted 68–74% of the total FA, with the essential PUFA; eicosapentaenoic acid (20:5ω3, EPA), arachidonic acid (20:4ω6, AA) and docosahexaenoic acid (22:6ω3, DHA), accounting for 42–44% of the total FA. High proportions of the saturated OC-FA 15:0 (7.1% in TC 01) and 17:0 (6.2% in TC 04) were detected. The OC-FA 17:1ω8 was present at 2.8% in TC 01. Of particular interest, the C₂₁ PUFA 21:5ω5 and 21:4ω7 were detected at 3.5% and 4.1%, respectively, in TC 04. A proposed biosynthesis pathway for these OC-PUFA is presented. It is possible that the unsaturated OC-PUFA found previously in a number of marine animals were derived from dietary thraustochytrids and they could be useful biomarkers in environmental and food web studies.     

Depression and adipose essential polyunsaturated fatty acids

The objective of the present study was to investigate the relation between adipose tissue polyunsaturated fatty acids, an index of long-term or habitual fatty acid dietary intake, and depression. The sample consisted of 247 healthy adults (146 males, 101 females) from the island of Crete. The number of subjects with complete data on all variables studied was 139. Subjects were examined at the Preventive Medicine and Nutrition Clinic of the University of Crete. Depression was assessed through the use of the Zung Self-rating Depression Scale. Mildly depressed subjects had significantly reduced (-34.6%) adipose tissue docosahexaenoic acid (DHA) levels than non-depressed subjects. Multiple linear regression analysis indicated that depression related negatively to adipose tissue DHA levels. In line with the findings of other studies, the observed negative relation between adipose tissue DHA and depression, in the present study, appears to indicate increasing long-term dietary DHA intakes with decreasing depression. This is the first literature report of a relation between adipose tissue DHA and depression. Depression has been reported to be associated with increased cytokine production, such as IL-1, IL-2, IL-6, INF-gamma and INF-alpha. On the other hand, fish oil and omega-3 fatty acids have been reported to inhibit cytokine synthesis. The observed negative relation between adipose DHA and depression, therefore, may stem from the inhibiting effect of DHA on cytokine synthesis.     

Inhibitory role of polyunsaturated fatty acids on lysophosphatidic acid-induced cancer cell migration and adhesion

Polyunsaturated fatty acids (PUFAs) have important pharmacological effects on mammalian cells. Here, we show that carboxyl group-containing PUFAs inhibit lysophosphatidic acid (LPA)-induced focal adhesion formation, thereby inhibiting migration and adhesion. Carboxyl group-containing PUFAs inhibit LPA-induced calcium mobilization, whereas ethyl ester-group containing PUFAs have no effect. In addition, carboxyl group-containing PUFAs functionally inhibit LPA-dependent RhoA activation. Given these results, we suggest that PUFAs may inhibit LPA-induced calcium/RhoA signaling pathways leading to focal adhesion formation. Carboxyl group-containing PUFAs may have a functional role in this regulatory mechanism.     

Effects of polyunsaturated fatty acids and clofibrate on chicken stearoyl-coA desaturase 1 gene expression

In chicken, adiposity is influenced by hepatic stearoyl-CoA desaturase (SCD) 1. This gene is up-regulated by low-fat high-carbohydrate diet and down-regulated by addition of polyunsaturated fatty acids (PUFA). In this study, we present evidence for an inhibition of chicken SCD1 expression by PUFA using reporter gene constructs in transient transfection assays. This inhibition does not involve the peroxisome proliferator-activated receptor pathway, in contrast with what has been observed in rodents. We were able to localise a PUFA as well as an insulin response element within the -372/+125 bp region of the promoter. Sequence analyses of this region allowed identification of several cis-regulatory elements: A sterol regulatory element (SRE) and a juxtaposed NF-Y element which have been shown to be involved in the regulation of mouse SCD genes by PUFA. In addition, we identified an overlapping Sp1/USF motif, which was described to play a role in insulin/glucose and PUFA regulation of fatty synthase, ATP-citrate-lyase, and leptin genes. These data provide the first characterisation of the chicken SCD1 promoter and putative cis-sequences involved in the regulation of this gene by PUFA and insulin.     

Biosynthesis of very-long-chain polyunsaturated fatty acids in transgenic oilseeds: constraints on their accumulation

Omega6- and omega3-polyunsaturated C20 fatty acids represent important components of the human diet. A more regular consumption and an accordingly sustainable source of these compounds are highly desirable. In contrast with the very high levels to which industrial fatty acids have to be enriched in plant oils for competitive use as chemical feedstocks, much lower percentages of very-long-chain polyunsaturated fatty acids (VLCPUFA) in edible plant oils would satisfy nutritional requirements. Seed-specific expression in transgenic tobacco (Nicotiana tabacum) and linseed (Linum usitatissimum) of cDNAs encoding fatty acyl-desaturases and elongases, absent from all agronomically important plants, resulted in the very high accumulation of Delta6-desaturated C18 fatty acids and up to 5% of C20 polyunsaturated fatty acids, including arachidonic and eicosapentaenoic acid. Detailed lipid analyses of developing seeds from transgenic plants were interpretated as indicating that, after desaturation on phosphatidylcholine, Delta6-desaturated products are immediately channeled to the triacylglycerols and effectively bypass the acyl-CoA pool. Thus, the lack of available Delta6-desaturated acyl-CoA substrates in the acyl-CoA pool limits the synthesis of elongated C20 fatty acids and disrupts the alternating sequence of lipid-linked desaturations and acyl-CoA dependent elongations. As well as the successful production of VLCPUFA in transgenic oilseeds and the identification of constraints on their accumulation, our results indicate alternative strategies to circumvent this bottleneck.     

Effects of dietary omega-6 and omega-3 fatty acids on levels of long chain polyunsaturated fatty acids in erythrocytes]

C18:2 omega 6/C18:3 omega 3 ratio was lowered in the diet of Elderly subjects. This was done by the replacement of usual sunflower oil by rapeseed oil or by supplementing soybean oil. This diet modification induced an increase of EPA (C20:5 omega 3) and DHA (C22:6 omega 3) in red cell phospholipids. The omega 6 fatty acids (C18:2 and C20:4) were slightly modified. Therefore, dietary C18:2 omega 6/C18:3 omega 3 ratio, seems to play an important role in the determination of membrane highly unsaturated fatty acid levels.     

Digestion and absorption of polyunsaturated fatty acids.

Polyunsaturated fatty acids play an important part in the structure and function of cellular membranes and are precursors of lipid mediators which play a key role in cardiovascular and inflammatory diseases. Dietary sources of essential fatty acids are vegetable oils for either linoleic or alpha-linolenic acids, and sea fish oils for eicosapentaenoic and docosahexaenoic acids. Because of the specificity of the pancreatic lipid hydrolases, triglyceride fatty acid distribution is an essential parameter in the digestibility of fats. The efficiency of the intestinal uptake depends on the hydrolysis and especially on their micellarization. n-3 polyunsaturated fatty acid ethyl ester digestion is recognized to be impaired, but n-3 polyunsaturated fatty acid triglyceride hydrolysis remains a controversial point, and to some authors explains differences observed between vegetable and fish oil absorption. So additional studies are required to investigate this intestinal step. In enterocytes, morphological and biochemical absorption processes involve reesterification of long-chain fatty acids and lipoprotein formation. At this level, specific affinity of I- and L-FABPc (cytosolic fatty acid binding proteins) to polyunsaturated fatty acids requires further investigation. A better understanding of the role of these FABPc might bring to light the esterification step, particularly the integration of polyunsaturated fatty acids into phospholipids. With reference to differences published between fish and vegetable oil absorption, longer-term absorption studies appear essential to some authors. Polyunsaturated fatty acid absorption is thought to be not very dissimilar to that of long-chain mono-unsaturated fatty acid absorption. However, several digestion and absorption specific steps are worth studying with reference to the crucial role of polyunsaturated fatty acids in the organism, and for example adaptation of possible dietary supplements.     

Elongation of polyunsaturated fatty acids in trypanosomatids

Leishmania major synthesizes polyunsaturated fatty acids by using Delta6, Delta5 and Delta4 front-end desaturases, which have recently been characterized [Tripodi KE, Buttigliero LV, Altabe SG & Uttaro AD (2006) FEBS J273, 271-280], and two predicted elongases specific for C18 Delta6 and C20 Delta5 polyunsaturated fatty acids, respectively. Trypanosoma brucei and Trypanosoma cruzi lack Delta6 and Delta5 desaturases but contain Delta4 desaturases, implying that trypanosomes use exogenous polyunsaturated fatty acids to produce C22 Delta4 fatty acids. In order to identify putative precursors of these C22 fatty acids and to completely describe the pathways for polyunsaturated fatty acid biosynthesis in trypanosomatids, we have performed a search in the three genomes and identified four different elongase genes in T. brucei, five in T. cruzi and 14 in L. major. After a phylogenetic analysis of the encoded proteins together with elongases from a variety of other organisms, we selected four candidate polyunsaturated fatty acid elongases. Leishmania major CAJ02037, T. brucei AAX69821 and T. cruzi XP_808770 share 57-52% identity, and group together with C20 Delta5 polyunsaturated fatty acid elongases from algae. The predicted activity was corroborated by functional characterization after expression in yeast. T. brucei elongase was also able to elongate Delta8 and Delta11 C20 polyunsaturated fatty acids. L. major CAJ08636, which shares 33% identity with Mortierella alpinaDelta6 elongase, showed a high specificity for C18 Delta6 polyunsaturated fatty acids. In all cases, a preference for n6 polyunsaturated fatty acids was observed. This indicates that L. major has, as predicted, Delta6 and Delta5 elongases and a complete pathway for polyunsaturated fatty acid biosynthesis. Trypanosomes contain only Delta5 elongases, which, together with Delta4 desaturases, allow them to use eicosapentaenoic acid and arachidonic acid, a precursor that is relatively abundant in the host, for C22 polyunsaturated fatty acid biosynthesis.     

Metabolism of polyunsaturated fatty acids and their toxicity to the microflora of the rumen

Ruminal microorganisms hydrogenate polyunsaturated fatty acids (PUFA) present in forages and thereby restrict the availability of health-promoting PUFA in meat and milk. The aim of this study was to investigate PUFA metabolism and the influence of PUFA on members of the ruminal microflora. Eleven of 26 predominant species of ruminal bacteria metabolised linoleic acid (LA; cis-9,cis-12–18:2) substantially. The most common product was vaccenic acid (trans-11–18:1), produced by species related to Butyrivibrio fibrisolvens. α-Linolenic acid (LNA; cis-9,cis-12,cis-15–18:3) was metabolised mostly by the same species. The fish oil fatty acids, eicosapentaenoic acid (EPA; 20:5(n − 3)) and docosahexaenoic acid (DHA; 22:6(n − 3)) were not metabolised. Cellulolytic bacteria did not grow in the presence of any PUFA at 50 μg ml⁻¹, nor did some butyrate-producing bacteria, including the stearate producer Clostridium proteoclasticum, Butyrivibrio hungatei and Eubacterium ruminantium. Toxicity to growth was ranked EPA > DHA > LNA > LA. Cell integrity, as measured using propidium iodide, was damaged by LA in all 26 bacteria, but to different extents. Correlations between its effects on growth and apparent effects on cell integrity in different bacteria were low. Combined effects of LA and sodium lactate in E. ruminantium and C. proteoclasticum indicated that LA toxicity is linked to metabolism in butyrate-producing bacteria. PUFA also inhibited the growth of the cellulolytic ruminal fungi, with Neocallimastix frontalis producing small amounts of cis-9,trans-11–18:2 (CLA) from LA. Thus, while dietary PUFA might be useful in suppressing the numbers of biohydrogenating ruminal bacteria, particularly C. proteoclasticum, care should be taken to avoid unwanted effects in suppressing cellulolysis.