Elongation predominates over desaturation in the metabolism of 18:3n-3 and 20:5n-3 in turbot (Scophthalmus maximus) brain astroglial cells in primary culture

Polyunsaturated fatty acids in fish tissues more closely resemble algal than terrestrial diet sources

The River Continuum Concept implies that consumers in headwater streams have greater dietary access to terrestrial basal resources, but recent studies have highlighted the dietary importance of high-quality algae. Algae provide consumers with physiologically important omega-3 (n-3) polyunsaturated fatty acids (PUFA), particularly eicosapentaenoic acid (EPA). However, terrestrial plants and most benthic stream algae lack the long-chain (LC) n-3 PUFA docosahexaenoic acid (DHA, 22:6n-3), which is essential for neural development in fish and other vertebrates. We sampled subalpine streams to investigate how the PUFA composition of neural (brain and eyes), muscle, and liver tissues of freshwater fish is related to their potential diets (macroinvertebrates, epilithon, fresh and conditioned terrestrial leaves). The PUFA composition of consumers was more similar to epilithon than to terrestrial leaves. Storage lipids of eyes most closely resembled dietary PUFA (aquatic invertebrates and algae). However, DHA and arachidonic acid (ARA, 20:4n-6) were not directly available in the diet but abundant in organs. This implies that algal PUFA were selectively retained or were produced internally via enzymatic PUFA conversion by aquatic consumers. This field study demonstrates the nutritional importance of algal PUFA for neural organs in aquatic consumers of headwater regions.

Dietary fish oil replacement with lard and soybean oil affects triacylglycerol and phospholipid muscle and liver docosahexaenoic acid content but not in the brain and eyes of surubim juveniles Pseudoplatystoma sp

Triplicate groups of juvenile suribim were fed for 183 days one of four different isonitrogenous (47.6% crude protein) and isolipidic (18.7% lipid) diets formulated using three different lipid sources: 100% fish oil (FO, diet 1); 100% pig lard (L, diet 2); 100% soybean oil (SO, diet 3), and FO/L/SO (1:1:1, w/w/w; diet 4). The tissue levels of fatty acids 18:2n-6 and 18:3n-3 decreased relative to corresponding dietary fatty acid values. The 20:5n-3 and 22:6n-3 composition of muscle and liver neutral lipids were linearly correlated with corresponding dietary fatty acid composition. In contrast, the 22:6n-3 composition of the brain and eye were similar among treatments. The 22:6n-3 level was enriched in all tissues, particularly in the neural tissues. Similar results were observed for tissue polar lipids: fatty acids content reflected dietary composition, with the exception of the 22:6n-3 level, which showed enrichment and no differences between groups. Given these results, the importance of the biochemical functions (transport and/or metabolism) of 22:6n-3 in the development of the neural system of surubim warrants further investigation.

Some insights into energy metabolism for osmoregulation in fish

A sufficient and timely energy supply is a prerequisite for the operation of iono- and osmoregulatory mechanisms in fish. Measurements of whole-fish or isolated-gill (or other organs) oxygen consumption have demonstrated regulation of the energy supply during acclimation to different osmotic environments, and such regulation is dependent on species, the situation of acclimation or acclimatization, and life habits. Carbohydrate metabolism appears to play a major role in the energy supply for iono- and osmoregulation, and the liver is the major source supplying carbohydrate metabolites to osmoregulatory organs. Compared with carbohydrates, the roles of lipids and proteins remain largely unclear. Energy metabolite translocation was recently found to occur between fish gill ionocytes and neighboring glycogen-rich (GR) cells, indicating the physiological significance of a local energy supply for gill ion regulatory mechanisms. Spatial and temporal relationships between the liver and other osmoregulatory and non-osmoregulatory organs in partitioning the energy supply for ion regulatory mechanisms during salinity challenges were also proposed. A novel glucose transporter was found to specifically be expressed and function in gill ionocytes, providing the first cue for investigating energy translocation among gill cells. Advanced molecular physiological approaches can be used to examine energy metabolism relevant to a particular cell type (e.g., gill ionocytes), and functional genomics may also provide another powerful approach to explore new metabolic pathways related to fish ion regulation.

Authentication of farmed and wild turbot (Psetta maxima) by fatty acid and isotopic analyses combined with chemometrics

Fatty acid composition and stable isotope ratios of carbon (delta(13)C) and nitrogen (delta(15)N) were determined in muscle tissue of turbot (Psetta maxima). The multivariate analysis of the data was performed to evaluate their utility in discriminating wild and farmed fish. Wild (n=30) and farmed (n=30) turbot of different geographical origins (Denmark, The Netherlands, and Spain) were sampled from March 2006 to February 2007. The application of linear discriminant analysis (LDA) and soft independent modeling of class analogy (SIMCA) to analytical data demonstrated the combination of fatty acids and isotopic measurements to be a promising method to discriminate between wild and farmed fish and between wild fish of different geographical origin. In particular, IRMS (Isotope Ratio Mass Spectrometry) alone did not permit us to separate completely farmed from wild samples, resulting in some overlaps between Danish wild and Spanish farmed turbot. On the other hand, fatty acids alone differentiated between farmed and wild samples by 18:2n-6 but were not able to distinguish between the two groups of wild turbot. When applying LDA isotope ratios, 18:2n-6, 18:3n-3, and 20:4n-6 fatty acids were decisive to distinguish farmed from wild turbot of different geographical origin, while delta(15)N, 18:2n-6, and 20:1n-11 were chosen to classify wild samples from different fishing zones. In both cases, 18:2n-6 and delta(15)N were determinant for classification purposes. We would like to emphasize that IRMS produces rapid results and could be the most promising technique to distinguish wild fish of different origin. Similarly, fatty acid composition could be used to easily distinguish farmed from wild samples.

Tissue essential fatty acid composition and competitive response to dietary manipulations in white bass (Morone chrysops), striped bass (M. saxatilis) and hybrid striped bass (M. chrysopsxM. saxatilis)

The effects of wide changes in dietary levels of docosahexaenoic (DHA) or arachidonic (ArA) acids on growth, survival and fatty acid composition in body tissues of Morone larvae were examined. White bass (WB, Morone chrysops), striped bass (SB, Morone saxatilis) and sunshine hybrid bass (HSB, M. chrysopsxM. saxatilis) larvae (day 24-46) were fed Artemia nauplii enriched with algal sources of varying proportions of DHA and ArA (from 0 to over 20% of total fatty acids). WB larvae fed DHA-deficient Artemia diet retarded over 50% of their potential growth, however, increasing dietary DHA/ArA ratios were associated with a significant growth improvement. The highest proportion of polyunsaturated fatty acids was found in WB neural tissue (approx. 50% of total fatty acids), while HSB neural tissue contained the highest proportion of saturated fatty acids (approx. 35% of total fatty acids). Within the neural tissues of all Morone larvae, both DHA and ArA were generally the most dominant as well as the most responding fatty acids to dietary manipulations (except in WB fed DHA or ArA deficient diets). HSB neural tissue was particularly efficient in retaining a significant amount of DHA in the face of dietary deficiency. However, WB neural tissue was the most responsive to dietary increase in DHA, accumulating a significantly higher amount of DHA (P<0.05) than SB or HSB. Results demonstrate significant differences in fatty acid composition and growth responsiveness to dietary manipulations between Morone larvae species and within specific tissues. WB weight gain and neural tissue composition was affected most by dietary changes in both DHA and ArA whereas SB and HSB tissue compositions were generally less affected by dietary manipulations.

The esterification and modification of n-3 and n-6 polyunsaturated fatty acids by hepatocytes and liver microsomes of turbot (Scophthalmus maximus)

The present study was undertaken to establish whether the formation of 22:6n-3 from 18:3n-3 and/or 20:5n-3 can occur in turbot liver and if this conversion is consistent with the operation of a Delta4 desaturase-independent pathway. At the same, time the effects of feeding a diet devoid of long chain polyunsaturated fatty acids (PUFA) on the patterns of esterification and modification of 18:3n-3, 20:5n-3 and 18:2n-6 by turbot hepatocytes and liver microsomes were examined. For this purpose, two groups of fish (25-30 g) were employed: one was fed a commercial diet containing fish oil (FO) and thus rich in long chain n-3 PUFA and the other was fed an experimental diet based on olive oil (OO). After 5 months of feeding, hepatocytes and liver microsomes isolated from individuals in the two groups of fish were incubated with [1-(14)C]-PUFA [either 18:3n-3, 20:5n-3 or 18:2n-6]. After 3 h of incubation, most radioactivity from all three radiolabelled substrates incorporated into lipids by hepatocytes and microsomes was recovered in the original substrate. The formation of desaturation products of n-3 radiolabelled substrates was higher in hepatocytes isolated from OO-fed than FO-fed fish. Small amounts of radiolabelled 22:6n-3 were formed from [1-(14)C]18:3n-3 and [1-(14)C]20:5n-3, but only by hepatocytes from fish fed OO, which also synthesised a small amount of radiolabelled 24:6n-3 from 14C-20:5n-3. Elongation products predominated over desaturation products in hepatic microsomes from both groups of fish studied, particularly in microsomes from fish fed FO. The results confirm that regardless of the long chain PUFA content of the diet, the production of 22:6n-3 in turbot liver from 18:3n-3 and/or 20:5n-3, and of 20:4n-6 from 18:2n-6, is very limited. The presence of radiolabelled 24:6n-3 in microsomes coupled with the absence of radiolabelled 22:6n-3 suggests that the formation of 22:6n-3 that does occur in turbot liver cells, may involve C24 intermediates and peroxisomal beta-oxidation.

Energy metabolism of fish brain

This review focuses on recent research on the metabolic function of fish brain. Fish brain is isolated from the systemic circulation by a blood-brain barrier that allows the transport of glucose, monocarboxylates and amino acids. The limited information available in fishes suggests that oxidation of exogenous glucose and oxidative phosphorylation provide most of the ATP required for brain function in teleosts, whereas oxidation of ketones and amino acids occurs preferentially in elasmobranchs. In several agnathans and benthic teleosts brain glycogen levels rather than exogenous glucose may be the proximate glucose source for oxidation. In situations when glucose is in limited supply, teleost brains utilize other fuels such as lactate or ketones. Information on use of lipids and amino acids as fuels in fish brain is scarce. The main pathways of brain energy metabolism are changed by several effectors. Thus, several parameters of brain energy metabolism have been demonstrated to change post-prandially in teleostean fishes. The absence of food in teleosts elicits profound changes in brain energy metabolism (increased glycogenolysis and use of ketones) in a way similar to that demonstrated in mammals though delayed in time. Environmental factors induce changes in brain energy parameters in teleosts such as the enhancement of glycogenolysis elicited by pollutants, increased capacity for anaerobic glycolysis under hypoxia/anoxia or changes in substrate utilization elicited by adaptation to cold. Furthermore, several studies demonstrate effects of melatonin, insulin, glucagon, GLP-1, cortisol or catecholamines on energy parameters of teleost brain, although in most cases the results are quite preliminary being difficult to relate the effects of those hormones to physiological situations. The few studies performed with the different cell types available in the nervous system of fish allow us to hypothesize few functional relationships among those cells. Future research perspectives are also outlined.

Docosahexaenoic acid is superior to eicosapentaenoic acid as the essential fatty acid for growth of grouper, Epinephelus malabaricus

Juvenile grouper (Epinephelus malabaricus) were fed seven experimental diets, one control diet and one reference diet for 12 wk to determine the dietary requirement of grouper for docosahexaenoic (DHA) and eicosapentaenoic (EPA) acids. Each of the seven diets contained 1 g/100 g DHA and EPA in various combinations and 9 g/100 g tristearin. The control diet contained 1 g/100 g trilinolenin and trilinolein (3:1, wt/wt), and no supplemental EPA or DHA. The reference diet contained only natural oils from a mixture of cod liver oil, linseed oil and safflower oil at a ratio of 2:1:1 (wt/wt/wt). Significant differences (P < 0.05) in growth were observed among the dietary treatments but not in survival rate or relative liver weight. Only the diet with the highest DHA/EPA ratio (3:1) promoted significantly greater growth than the control diet. Purified EPA and DHA did not perform better in promoting growth than did the impure EPA and DHA oils. Enhanced growth was observed when the dietary DHA/EPA ratio was greater than 1, indicating that DHA was superior to EPA in promoting fish growth. Neutral lipid (NL) was the predominant lipid fraction (>70%) in both liver and muscle. Tissue NL/polar lipid did not differ among groups except the reference diet group that had a higher ratio (P < 0.05). DHA and EPA levels in the grouper tissues, especially muscle, were highly reflective of dietary levels of DHA and EPA, indicating that direct incorporation was likely. In addition, the 20:1(n-9), concentration in NL fractions seems to be an appropriate indicator of dietary essential fatty acid deficiency in grouper.

The effect of ethanol and acetaldehyde on microsomal and mitochondrial membrane fatty acid profiles in cultured rat astroglia

It has been shown that free radical damage may be involved in ethanol-induced cytotoxicity in cultured neural cells. Since changes in oxidative metabolism and the resulting lipid peroxidation readily modify biological membranes and alter cell functions we studied the effect of ethanol and its metabolite acetaldehyde on rat astroglial fatty acids profiles in the most common lipid classes of mitochondrial and microsomal membranes, i.e. phosphatidylcholine (PC) and phosphatidylethanolamine (PE). Rat astroglial cells were grown for 1 week in the presence of 50 m M or 100 m M ethanol. To examine acetaldehyde effects we used a 4-day co-culture model consisting of astroglial cells and alcohol dehydrogenase-transfected Chinese hamster ovary (CHO) cells. Acetaldehyde produced by these cells reached 172 mu M and 265 mu M, respectively, for ethanol concentrations of 10 and 20 m M. Mitochondrial and microsomal membranes were prepared by differential centrifugation, phosphatidylcholine and phosphatidylethanolamine were separated using thin layer chromatography and fatty acid quantitation was performed by GLC. Neither ethanol nor acetaldehyde changed the mitochondrial phosphatidylcholine or phosphatidylethanolamine profiles of total saturated, mono-unsaturated or polyunsaturated fatty acids. However, some significant alterations in particular fatty acids appeared especially after acetaldehyde but also after the highest ethanol dose. In microsomal phosphatidylcholine monounsaturated fatty acids were significantly increased after both, ethanol and acetaldehyde exposure. Among polyunsaturated fatty acids, arachidonic acid was found to be especially affected by both ethanol and acetaldehyde. Similar decreases were observed in adrenic, docosapentaenoic and docosahexaenoic acids in the groups treated with ethanol. In microsomal phosphatidylethanolamine, ethanol and acetaldehyde decreased monounsaturated and some polyunsaturated fatty acids. These data support the role of peroxidative processes in cultured rat astroglia exposed to ethanol and point to the role of acetaldehyde in this mechanism.

Growth, mortality, tissue histopathology and fatty acid compositions, eicosanoid production and response to stress, in juvenile turbot fed diets rich in gamma-linolenic acid in combination with eicosapentaenoic acid or docosahexaenoic acid

Three diets containing either borage oil (BO) and southern hemisphere fish oil Marinol (MO), or BO and tuna orbital oil (TO), or a northern hemisphere fish oil (FO) were fed to duplicate groups of turbot (Scophthalmus maximus) of initial mean weight 1.2 g for a period of 12 weeks. The BO/MO and BO/TO diets were enriched in gamma-linolenic (18:3n-6, GLA) and eicosapentaenoic (20:5n-3, EPA) acids, and GLA and docosahexaenoic acid (22:6n-3, DHA), respectively. No differences were observed in final weights or growth rates, either between duplicate tanks or between dietary treatments. Half of the FO-fed fish sampled showed a histopathological lesion indicative of lipoid liver degeneration while the other treatments only showed a slight incidence of the same pathology. The fatty acid compositions of carcass and tissues broadly reflected the dietary input. In general, fish fed the BO/MO diet had increased levels of 18:2n-6, 18:3n-6, 20:3n-6 and 20:5n-3, but a lower level of 22:6n-3, compared to fish fed FO. In fish fed the BO/TO diet, levels of 18:2n-6, 18:3n-6, 20:3n-6 and 20:4n-6 were increased while levels of 20:5n-3 and 22:5n-3 were reduced, compared to fish fed FO. Concentrations of thromboxanes B (TXB) and leukotrienes B (LTB), derived from 20:4n-6 and 20:5n-3, were measured in plasma and stimulated blood cells. Levels of TXB2 were greatest in fish fed the BO/TO diet compared to both other treatments, while LTB4 was decreased in fish fed the BO/MO diet compared to both other treatments. In a stress test which involved anaesthesia followed by measurement of recovery times, fish fed the BO/MO diet had significantly lower recovery times compared to fish fed the FO diet.

Modulation of norepinephrine-stimulated cyclic AMP accumulation in rat pinealocytes by n-3 fatty acids

This work showed that docosahexaenoic (22:6n-3) and eicosapentaenoic (20:5n-3) acid supplementation for 48 h have opposite effects on the norepinephrine-stimulated cyclic AMP accumulation in rat pinealocytes. We found that 22:6n-3 supplementation of pineal cells, done by increasing specifically 22:6n-3 in phospholipid and triacylglycerol pools, led to inhibition of norepinephrine-stimulated cyclic AMP production whereas 20:5n-3 supplementation, by increasing 20:5n-3, and 22:5n-3 and 22:6n-3 in the same pools, stimulated it. In contrast, direct treatment of pinealocytes with each fatty acid (50 microM) did not affect cyclic AMP production in the presence of (0.1-10 microM) norepinephrine. The results indicate that, using pharmacological agents such as forskolin or prazosin: (a) neither basal nor forskolin-stimulated cyclic AMP levels were modified in fatty acid-supplemented cells compared to control cells; (b) in the presence of 1 microM prazosin, the activation by 20:5n-3 was still effective whereas no additional inhibition of norepinephrine stimulation was observed in 22:6n-3-supplemented cells. Taken together our results suggest that 22:6n-3 or 20:5n-3 supplementation modulates specifically the alpha 1- or beta-adrenoceptors in the rat pineal gland.

Production of eicosanoids derived from 20:4n-6 and 20:5n-3 in primary cultures of turbot (Scophthalmus maximus) brain astrocytes in response to platelet activating factor, substance P and interleukin-1 beta

Primary cultures of turbot (Scophthalmus maximus) brain astroglial cells established in medium containing fetal bovine serum contain increased proportions of 18:1(n-9), total (n-9) and (n-6) polyunsaturated fatty acids (PUFA) and greatly reduced (n-3) PUFA in comparison with turbot brain. Supplementation with a mixture of 5 microM eicosapentaenoic [20:5(n-3)] and 25 microM docosahexaenoic [22:6(n-3)] acids for 4 days significantly increased the percentages of these acids in total cellular lipid of turbot astrocytes and restored the (n-3) PUFA composition of the cells to that found in turbot brain. The production of prostaglandins (PG) E and F of the 2- and 3-series and leukotrienes (LT) C4 and C5 in response to various agonists was determined in PUFA-supplemented astrocytes. Calcium ionophore A23187, platelet activating factor and substance P stimulated the production of both PGF and PGE. Interleukin-1 beta significantly stimulated the production of PGF only. There were differences between the agonists in their effects on the relative levels of 2- and 3-series PGs produced. Only very low amounts of LTC were produced by the turbot astrocytes, with only substance P showing a minor stimulatory effect.

Diets rich in eicosapentaenoic acid and gamma-linolenic acid affect phospholipid fatty acid composition and production of prostaglandins E1, E2 and E3 in turbot (Scophthalmus maximus), a species deficient in delta 5 fatty acid desaturase

Duplicate groups of juvenile turbot, (Scophthalmus maximus), were fed diets containing either Marinol K (MO), a marine fish oil rich in eicosapentaenoic acid (EPA; 20:5, n-3) or borage oil (BO), rich in gamma-linolenic acid (GLA; 18:3, n-6), for a period of 12 weeks. Individual phospholipid fatty acid compositions from hearts of fish fed BO had significantly more 18:2, n-6, GLA, 20:2, n-6, dihomo-gamma-linolenic acid (DHGLA; 20:3, n-6) and total n-6 polyunsaturated fatty acids (PUFA), but significantly less arachidonic acid (AA; 20:4, n-6), compared to fish fed MO. In both phosphatidylcholine (PC) and phosphatidylethanolamine (PE) from heart, the DHGLA was increased by over 50-fold in fish fed BO while AA was reduced by over two-thirds, compared to fish fed MO. In brain, EPA was the major C20 PUFA, i.e. potential eicosanoid precursor in all phospholipids from fish fed MO, with the EPA level being twice that of AA in brain phosphatidylinositol (PI). DHGLA was the major C20 PUFA in all phospholipid classes from fish fed BO. In kidney and gill, EPA was the predominant C20 PUFA in all phospholipid classes, except PI, in fish fed MO. In kidney of fish fed BO, DHGLA was the major C20 PUFA in all phospholipid classes, except PE. In gill of fish fed BO, DHGLA was the major C20 PUFA in all phospholipid classes, including PI, where DHGLA was over 2.5-fold greater than AA. In homogenates of heart, kidney and gill from BO-fed fish the prostaglandin E1 (PGE1) concentration was significantly increased compared to MO-fed fish. In heart and kidney homogenates from fish fed MO the PGE3 concentration was significantly increased compared to fish fed BO. The ratio of PGE2/PGE1 was significantly reduced in brain, heart, kidney and gill homogenates from fish fed BO compared to those fed MO.

Effects of dietary borage oil [enriched in γ-linolenic acid,18:3(n-6)] or marine fish oil [enriched in eicosapentaenoic acid,20:5(n-3)] on growth, mortalities, liver histopathology and lipid composition of juvenile turbot (Scophthalmus maximus)

A marine fish oil, Marinol K (MO) and borage oil (BO) were used to formulate diets relatively rich in eicosapentaenoic acid [EPA; 20:5(n-3)] and γ-linolenic acid [GLA; 18:3(n-6)], respectively. The diets were fed to duplicate groups of juvenile turbot (Scophthalmus maximus) of initial weight 1.4 g for a period of 12 weeks. No differences were observed in final weights either between duplicate tanks or between dietary treatments. Mortalities in the MO-fed group were significantly greater than in the BO-fed group. In the MO-fed group, 7 out of 12 fish sampled for histological analysis showed a pronounced liver histopathology whereas only 1 of 12 fish sampled in the BO-fed group showed slight pathology. EPA levels were increased 2.2-fold and its elongation product, 22:5(n-3), was increased 1.8-fold while arachidonic acid [AA; 20:4(n-6)] was decreased by 30% in MO-fed fish compared to the initial carcass composition. GLA was increased 53-fold and its elongation product dihomo-γ-linolenic acid [DHGLA; 20:3(n-6)] was increased 16-fold while AA was reduced by 90% in BO-fed fish compared to the initial carcass composition. The amount of triacylglycerol in liver of BO-fed fish was significantly greater than levels in MO-fed fish. The fatty acid compositions of individual phospholipids from liver showed marked differences between dietary treatments. Fish fed MO had significantly higher levels of the (n-3) polyunsaturated fatty acids (PUFA), 20:5(n-3), 22:5(n-3) and 22:6(n-3), and also significantly more 20:4(n-6) compared to BO-fed fish which had significantly higher 18:2(n-6), 18:3(n-6), 20:2(n-6) and 20:3(n-6). The composition of liver phosphatidylinositol was particularly unusual in BO-fed fish having DHGLA as the major C20 PUFA which was 2.2-fold greater than AA and 3.9-fold greater than EPA. This study demonstrates that the carcass composition of turbot can be altered, by means of dietary lipids, to contain increased levels of EPA and DHGLA which would be of potential benefit in human as well as in fish nutrition. However, caution should be exercised when using very highly unsaturated oils relatively rich in EPA which may generate histopathological lesions in the fish.

Effects of different dietary arachidonic acid : docosahexaenoic acid ratios on phospholipid fatty acid compositions and prostaglandin production in juvenile turbot (Scophthalmus maximus)

Five purified diets containing AA (20:4n-6) at 0.02-0.78% dry weight and DHA (22:6n-3) at 0.93-0.17% dry weight were fed to duplicate groups of juvenile turbot (Scophthalmus maximus) of initial weight 0.87 g for a period of 11 weeks. The dietary DHA:AA ratio ranged from 62 to 0.2. Incorporation of AA into liver phospholipids increased with increasing dietary AA input. Phospholipids from fish fed diets containing 0.02, 0.06 and 0.11% of dry weight as AA generally contained less AA compared to fish fed fish oil while those fed diets containing 0.35 and 0.78% of dry weight as AA had higher AA levels in their phospholipids. The highest levels of AA were found in PI but the greatest percentage increase in AA incorporation was in PE and PC. Brain phospholipid fatty acid compositions were less altered by dietary treatment than those of liver but DHA content of PC and PE in brain was substantially lower in fish fed 0.93% pure DHA compared to those fed fish oil. This suggests that dietary DHA must exceed 1% of dry weight to satisfy the requirements of the developing neural system in juvenile turbot. In both tissues, (20:5n-3) concentration was inversely related to both dietary and tissue PI AA concentration. Similar dietary induced changes in AA, EPA and DHA concentrations occurred in the phospholipids of heart, gill and kidney. PGE2 and 6-ketoPGF1α were measured in homogenates of heart, brain, gill and kidney. In general, fish fed the lowest dietary AA levels had reduced levels of prostaglandins in their tissue homogenates while those fed the highest level of AA had increased prostaglandin levels, compared to fish fed fish oil. In brains, the PGE2 concentration was only significantly increased in fish fed the highest dietary AA.

Diversity in the ability of cultured cells to elongate and desaturate essential (n-6 and n-3) fatty acids

Essential fatty acids (EFAs) cannot be synthesized by mammalian cells. Once taken in with the diet, they can undergo desaturations/saturations and chain elongations/shortenings to yield a variety of polyunsaturated fatty acids of the same family. Cells in vitro from a variety of tissues are capable of processing EFAs to varying extents. Conversion of the parent EFAs, linoleic (LA, n-6) and alpha-linolenic (LNA, n-3) acids, to the 20-carbon polyunsaturated fatty acids, arachidonic (AA, n-6) and eicosapentanoic (EPA, n-3), requires chain elongation and delta 6 and delta 5 desaturations. AA and EPA are required by many tissues for optimal biological function and are precursors of biologically active eicosanoid hormones. All cultured cells are able to elongate exogenous LA and LNA, and most can perform delta 5 desaturation, so delta 6 desaturation is the limiting step in AA and EPA production. Longer fatty acids that have more double bonds than AA or EPA are less frequently produced due to a deficiency in delta 4 desaturating ability. The process of retroconversion (chain shortening) is less extensively studied, but evidence from a variety of cells suggests that this type of metabolic conversion is normally active. The example of MCF-7 (human breast cancer cell line) and MCF-10A cells (human noncancerous breast cell line) is discussed in order to emphasize the diversity in EFA processing ability of cultured cells. Under identical culture conditions, MCF-10A cells perform extensive desaturations, elongations, and retroconversions, whereas MCF-7 cells can only elongate and retroconvert exogenous EFAs. Given the great diversity in the ability of cultured cells to process EFAs, no conclusions can be drawn regarding the mechanisms responsible for the effects of exogenous EFAs on a particular cell until that cell's EFA processing patterns have been evaluated.

Effects of diets rich in linoleic (18:2n - 6) and α-linolenic (18:3n - 3) acids on the growth, lipid class and fatty acid compositions and eicosanoid production in juvenile turbot (Scophthalmus maximus L.)

Three practical-type diets utilizing fishmeal and casein as the protein sources and containing fish oil (FO), safflower oil (SO) or linseed oil (LO) were fed to duplicate groups of juvenile turbot (Scophthalmus maximus) of initial weight 1.2 g for a period of 12 weeks. No differences in final weight, mortality or development of pathological lesions were evident either between duplicate tanks or between dietary treatments over this period. Fish fed diets containing SO and LO contained significantly greater amounts of liver triacylglycerol compared to fish fed FO. The major C18 polyunsaturated fatty acids (PUFA) in SO and LO diets, 18:2(n-6) and 18:3(n-3) respectively, were readily incorporated into both total lipid and individual phospholipids of turbot tissues. There was no accumulation of the Δ6-desaturation products of these fatty acids, namely 18:3(n-6) and 18:4(n-3), in any of the tissues examined. The products of elongation of 18:2(n-6) and and 18:3(n-3), 20:2(n-6) and 20:3(n-3) respectively, accumulated in both total lipid and phospholipids with the highest levels of 20:2(n-6) in liver PC and 20:3(n-3) in liver PE. Eicosapentaenoic acid [EPA, 20:5(n-3)] levels exceeded those of arachidonic acid [AA, 20:4(n-6)] in phosphatidylinositol (PI) from liver and gill of fish fed LO. EPA levels in liver PI from fish fed LO were 3-fold and 2-fold greater than SO-fed and FO-fed fish, respectively. Fish fed diets containing SO and LO had significantly reduced levels of AA in liver and muscle total lipid and lower AA in individual phospholipid classes of liver and gill compared to FO-fed fish. The concentration of thromboxane B2 was significantly reduced in plasma and isolated gill cells stimulated with calcium ionophore A23187 of fish fed SO and LO compared to those fed FO. Prostaglandin E produced by isolated gill cells stimulated with A23187 was significantly reduced in fish fed both SO and LO compared to fish fed FO.

Effect of supplementation with 20:3(n-6), 20:4(n-6) and 20:5(n-3) on the production of prostaglandins E and F of the 1-, 2- and 3-series in turbot (Scophthalmus maximus) brain astroglial cells in primary culture

The production of prostaglandins E and F of the 1-, 2- and 3-series was determined in primary cultures of turbot (Scophthalmus maximus) brain astroglial cells after supplementation with 25 microM dihomo-gamma-linolenic (20:3(n-6)), arachidonic (20:4(n-6)) and eicosapentaenoic (20:5(n-3)) acids. Supplementation by 20:3(n-6), 20:4(n-6) and 20:5(n-3) for 4 days significantly increased the percentages of the respective acids in the total cellular lipid of the turbot astrocytes. The predominant prostaglandins formed by turbot astrocytes in response to stimulation with calcium ionophore A23187 were prostaglandin E2 and prostaglandin F2 alpha under all experimental conditions. The production of prostaglandin E2 was stimulated 2.6-fold, but prostaglandin F2 alpha production was unaffected after supplementation of cultures with 20:4(n-6). However, prostaglandin E2 production in astrocytes was significantly inhibited 3- and 4-fold, and prostaglandin F2 alpha was inhibited 1.6- and 14.6-fold by supplementation with 20:3(n-6) and 20:5(n-3), respectively. Supplementation with 20:3(n-6) also significantly increased the production of prostaglandin E1 (almost 4-fold) and prostaglandin F1 alpha (2.2-fold) whereas supplementation with 20:5(n-3) did not significantly increase the production of prostaglandin E3. Prostaglandin F3 alpha but not prostaglandin E1 were significantly reduced in 20:5(n-3)-supplemented cultures.

Diverse effects of essential (n-6 and n-3) fatty acids on cultured cells

Fatty acids (FAs) have long been recognized for their nutritional value in the absence of glucose, and as necessary components of cell membranes. However, FAs have other effects on cells that may be less familiar. Polyunsaturated FAs of dietary origin (n-6 and n-3) cannot be synthesized by mammals, and are termed 'essential' because they are required for the optimal biologic function of specialized cells and tissues. However, they do not appear to be necessary for normal growth and metabolism of a variety of cells in culture. The essential fatty acids (EFAs) have received increased attention in recent years due to their presumed involvement in cardiovascular disorders and in cancers of the breast, pancreas, colon and prostate. Many in vitro systems have emerged which either examine the role of EFAs in human disease directly, or utilize EFAs to mimic the in vivo cellular environment. The effects of EFAs on cells are both direct and indirect. As components of membrane phospholipids, and due to their varying structural and physical properties, EFAs can alter membrane fluidity, at least in the local environment, and affect any process that is mediated via the membrane. EFAs containing 20 carbons and at least three double bonds can be enzymatically converted to eicosanoid hormones, which play important roles in a variety of physiological and pathological processes. Alternatively, EFAs released into cells from phospholipids can act as second messengers that activate protein kinase C. Furthermore, susceptibility to oxidative damage increases with the degree of unsaturation, a complication that merits consideration because lipid peroxidation can lead to a variety of substances with toxic and mutagenic properties. The effects of EFAs on cultured cells are illustrated using the responses of normal and tumor human mammary epithelial cells. A thorough evaluation of EFA effects on commercially important cells could be used to advantage in the biotechnology industry by identifying EFA supplements that lead to improved cell growth and/or productivity.