Effect of rapeseed oil and dietary n-3 fatty acids on triacylglycerol synthesis and secretion in Atlantic salmon hepatocytes

Fish oil (FO) has traditionally been used as the dominating lipid component in fish feed. However, FO is a limited resource and the price varies considerably, which has led to an interest in using alternative oils, such as vegetable oils (VOs), in fish diets. It is far from clear how these VOs affect liver lipid secretion and fish health. The polyunsaturated fatty acids (PUFAs), eicosapentanoic acid (EPA) and docosahexanioc acid (DHA), reduce the secretion of lipoproteins rich in triacylglycerols (TAGs) in Atlantic salmon, as they do in humans. The mechanism by which n-3 fatty acids (FAs) in the diet reduce TAG secretion is not known. We have therefore investigated the effects of rapeseed oil (RO) and n-3 rich diets on the accumulation and secretion of (3)H-glycerolipids by salmon hepatocytes. Salmon, of approximately 90 g were fed for 17 weeks on one of four diets supplemented with either 13.5% FO, RO, EPA-enriched oil or DHA-enriched oil until a final average weight of 310 g. Our results show that the dietary FA composition markedly influences the endogenous FA composition and lipid content of the hepatocytes. The intracellular lipid level in hepatocytes from fish fed RO diet and DHA diet were higher, and the expressions of the genes for microsomal transfer protein (MTP) and apolipoprotein A1 (Apo A1) were lower, than those in fish fed the two other diets. Secretion of hepatocyte glycerolipids was lower in fish fed the EPA diet and DHA diet than it was in fish fed the RO diet. Our results indicate that EPA and DHA possess different hypolipidemic properties. Both EPA and DHA inhibit TAG synthesis and secretion, but only EPA induces mitochondrial proliferation and reduce intracellular lipid. Expression of the gene for peroxisome proliferator-activated receptor alpha (PPARalpha) was higher in the DHA dietary group than it was in the other groups.     

Docosahexaenoic acid synthesis from alpha-linolenic acid is inhibited by diets high in polyunsaturated fatty acids

The conversion of the plant-derived omega-3 (n-3) α-linolenic acid (ALA, 18:3n-3) to the long-chain eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3) can be increased by ALA sufficient diets compared to ALA deficient diets. Diets containing ALA above an optimal level result in no further increase in DHA levels in animals and humans. The present study evaluates means of maximizing plasma DHA accumulation by systematically varying both linoleic acid (LA, 18:2n-6) and ALA dietary level. Weanling rats were fed one of 54 diets for three weeks. The diets varied in the percentage of energy (en%) of LA (0.07–17.1 en%) and ALA (0.02–12.1 en%) by manipulating both the fat content and the balance of vegetable oils. The peak of plasma phospholipid DHA (>8% total fatty acids) was attained as a result of feeding a narrow dietary range of 1–3 en% ALA and 1–2 en% LA but was suppressed to basal levels (～2% total fatty acids) at dietary intakes of total polyunsaturated fatty acids (PUFA) above 3 en%. We conclude it is possible to enhance the DHA status of rats fed diets containing ALA as the only source of n-3 fatty acids but only when the level of dietary PUFA is low (<3 en%).     

N-3 HUFAs affect fat deposition,susceptibility to oxidative stress,and apoptosis in Atlantic salmon visceral adipose tissue

We have investigated how n-3 highly unsaturated fatty acids (HUFAs) in the diet affect fatty acid (FA) utilization, fat storage and oxidative stress (OS) in Atlantic salmon (Salmo salar) white adipose tissue (WAT). Four groups of Atlantic salmon were fed for 21 weeks on one of the four diets supplemented with 23% (of dry matter) lipid. Docosahexaenoic acid (DHA; 22:6n-3) and eicosapentaenoic acid (EPA; 20:5n-3) levels increased from 10% of total FAs in the rapeseed oil (RO) diet, to 20% in the fish oil (FO) diet, and to 50% and 55% in the DHA-enriched and EPA-enriched diets, respectively. Increased dietary levels of n-3 HUFAs resulted in lower fat percentage in WAT. Furthermore, mitochondrial FA β-oxidation activity was higher in the FO group than it was in the RO group. The relative levels of DHA and EPA in phospholipids (PLs) from WAT and mitochondrial membranes increased with the increasing dietary levels of these HUFAs. In general, the mitochondrial membrane PLs were characterised by lower relative levels of n-3 HUFAs and higher relative levels of linoleic acid (LA; 18:2 n-6) than WAT membrane PLs. The predominance of LA relative to n-3 HUFAs in mitochondrial membrane PLs may help to protect these PLs from peroxidation. Cytochrome c oxidase measurements revealed higher incidence of disrupted mitochondrial membranes in the DHA and EPA dietary groups than in the FO and RO dietary groups. This disruption further affected the mitochondrial function, resulting in a marked reduction in FA β-oxidation capacities. The reduction in mitochondrial function and the increase in the activity of superoxide dismutase (SOD) in the DHA and EPA groups showed that high dietary dose of DHA and EPA resulted in oxidative stress (OS). The increased activity of caspase 3 in the high n-3 HUFA groups suggested the induction of apoptosis and increased incidence of cell death in WAT, which may be one of the factors explaining the lower fat percentage found in these groups.     

Divergent effects of eicosapentaenoic and docosahexaenoic acid ethyl esters, and fish oil on hepatic fatty acid oxidation in the rat

The physiological activity of fish oil, and ethyl esters of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) affecting hepatic fatty acid oxidation was compared in rats. Five groups of rats were fed various experimental diets for 15 days. A group fed a diet containing 9.4% palm oil almost devoid of n-3 fatty acids served as a control. The test diets contained 4% n-3 fatty acids mainly as EPA and DHA in the form of triacylglycerol (9.4% fish oil) or ethyl esters (diets containing 4% EPA ethyl ester, 4% DHA ethyl ester, and 1% EPA plus 3% DHA ethyl esters). The lipid content of diets containing EPA and DHA ethyl esters was adjusted to 9.4% by adding palm oil. The fish oil diet and ethyl ester diets, compared to the control diet containing 9.4% palm oil, increased activity and mRNA levels of hepatic mitochondrial and peroxisomal fatty acid oxidation enzymes, though not 3-hydroxyacyl-CoA dehydrogenase activity. The extent of the increase was, however, much greater with the fish oil than with EPA and DHA ethyl esters. EPA and DHA ethyl esters, compared to the control diet, increased 3-hydroxyacyl-CoA dehydrogenase activity, but fish oil strongly reduced it. It is apparent that EPA and DHA in the form of ethyl esters cannot mimic the physiological activity of fish oil at least in affecting hepatic fatty acid oxidation in rat.     

Differential effects of docosahexaenoic acid and eicosapentaenoic acid on suppression of lipoxygenase pathway in peritoneal macrophages

Docosahexaenoic acid (DHA) or eicosapentaenoic acid (EPA) was facilely incorporated into phospholipids of mouse peritoneal macrophages following incubation with pure fatty acids complexed to bovine serum albumin. Following stimulation with calcium ionophore A23187, the DHA-enriched cells synthesized significantly smaller amounts of leukotriene C4 and leukotriene B4 compared to control or EPA-enriched cells. The EPA-enriched cells synthesized lower amounts of leukotriene C4 and leukotriene B4 compared to control cells. The stimulated macrophages utilized endogenously released arachidonic acid for leukotriene B4 and leukotriene C4 synthesis. Exogenous arachidonic acid increased the formation of 12-hydroxyeicosatetraenoic acid (12-HETE) and 15-HETE and macrophages enriched with DHA or EPA produced similar amounts of 12-HETE and 15-HETE compared to control cells. These studies demonstrated that the synthesis of leukotriene C4, leukotriene B4 and HETE in macrophages is differentially affected by DHA and EPA.     

Whole-body synthesis secretion of docosahexaenoic acid from circulating eicosapentaenoic acid in unanesthetized rats

Dietary docosahexaenoic acid (DHA; 22:6n-3) and eicosapentaenoic acid (EPA; 20:5n-3) are considered important for maintaining normal heart and brain function, but little EPA is found in brain, and EPA cannot be elongated to DHA in rat heart due to the absence of elongase-2. Ingested EPA may have to be converted in the liver to DHA for it to be fully effective in brain and heart, but the rate of conversion is not agreed on. This rate was determined in male adult rats fed a standard n-3 PUFA, containing diet by infusing unesterified albumin-bound [U-¹³C]EPA intravenously for 2 h and measuring esterified [¹³C]labeled PUFAs in arterial plasma lipoproteins, as well as the specific activity of unesterified plasma EPA. Whole-body (presumably hepatic) synthesis secretion rates from circulating unesterified EPA, calculated from peak first derivatives of plasma esterified concentration × volume curves, equaled 2.61 μmol/day for docosapentaenoic acid (22:5n-3) and 5.46 μmol/day for DHA. The DHA synthesis rate was 24-fold greater than the reported brain DHA consumption rate in rats. Thus, dietary EPA could help to maintain brain and heart DHA homeostasis because it is converted at a relatively high rate in the liver to circulating DHA.     

Eicosapentaenoic acid pre-treatment reduces biochemical changes induced in total brain and myelin of weanling Wistar rats by cuprizone feeding

Recently, we investigated the effects of eicosapentaenoic acid (EPA), a fatty acid which modulates immune response and stimulates myelin gene expression, in an established model of multiple sclerosis (MS): the experimental autoimmune encephalomyelitis (EAE) induced in Dark Agouti rats. As scientific evidences and our previous studies have suggested that EPA could directly affect oligodendrocytes, we have now evaluated the effects of EPA in the non-immune mediate MS model characterized by selective oligodendrocytes damage induced by cuprizone (CPZ).We found that feeding weanling rats diets containing 0.6% CPZ for 2 weeks induced variation of whole brain and myelin biochemical composition representative of a severe myelin damage. We thus administered daily and by gavage EPA or PBS to 2-day old rats up to 21 days. Afterwards, rats were fed CPZ diet for 9 days. The results show that compared to PBS/CPZ fed rats, the whole brain cerebroside content in EPA pre-treated rats was statistically increased as well as there was an overall trend of increase of all other biochemical components.     

Erythrocyte eicosapentaenoic acid versus docosahexaenoic acid as a marker for fish and fish oil consumption.

The fatty acid composition of erythrocyte membranes was investigated in 21 healthy men after 6 wk of varying intakes of eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3). In one experiment, 12 subjects were fed three diets in a 3 x 3 crossover design: an essentially fish-free control diet, a fish diet (0.15 g EPA/d, 0.41 g DHA/d) and the same fish-based diet supplemented with 5 g/d fish oil (Fish + Oil: 0.99 g EPA/d, 0.99 g DHA/d). A 6 wk wash-out period was allowed between each diet. In another experiment, 11 subjects were supplemented with 5 g/d fish oil alone for 6 wk (0.84 g EPA/d, 0.48 g DHA/d). After fish or fish oil feeding, the percent proportion of EPA and DHA in the erythrocyte membranes rose at the expense of linoleic and arachidonic acids. After 6 wk on the fish-based diets, EPA incorporation approached saturation, with the incremental increases being proportional to the amounts supplied by the diets. In contrast, parallel increases were observed for erythrocyte DHA even though the Fish + Oil diet was supplying twice as much DHA as the fish alone diet. These observations imply different metabolic rates for EPA and DHA and their importance is discussed in terms of the value of erythrocyte EPA versus DHA as markers for fish and fish oil consumption.     

Suppression of hepatic fatty acid synthase by feeding alpha-linolenic acid rich perilla oil lowers plasma triacylglycerol level in rats

This study was performed to determine the effects of dietary perilla oil, a n-3 alpha-linolenic acid (ALA) source, on hepatic lipogenesis as a possible mechanism of lowering triacylglycerol (TG) levels. Male Sprague-Dawley rats were trained for a 3-hour feeding protocol and fed one of five semipurified diets as follows: 1% (w/w) corn oil control diet, or one of four diets supplemented with 10% each of beef tallow, corn oil, perilla oil, and fish oil. Two separate experiments were performed to compare the effects of feeding periods, 4 weeks and 4 days. Hepatic and plasma TG levels were decreased in rats fed perilla oil and fish oil diets, compared with corn oil and beef tallow diets. The activities of hepatic lipogenic enzymes such as fatty acid synthase (FAS), glucose-6-phosphate dehydrogenase, and malic enzyme were suppressed in the fish oil, perilla oil, and corn oil-fed groups, and the effect was the most significant in the fish oil-fed group. Also, the activities of glycolytic enzymes, glucokinase, and L-pyruvate kinase showed the similar trend as that of lipogenic enzymes. The activity of FAS, the key regulatory enzyme in lipogenesis, was positively correlated with hepatic and plasma TG levels and reduced significantly in the perilla oil-fed group compared with corn oil-fed group. In addition, the FAS activity was negatively correlated with the hepatic microsomal content of EPA and DHA. In conclusion, suppression of FAS plays a significant role in the hypolipidemic effects observed in rats fed ALA rich perilla oil and these effects were associated with the increase of hepatic microsomal EPA and DHA contents.     

Partial replacement of dietary fish oil with blends of vegetable oils (rapeseed, linseed and palm oils) in diets for European sea bass (Dicentrarchus labrax L.) over a long term growth study: effects on muscle and liver fatty acid composition and effectiveness of a fish oil finishing diet

Triplicate groups of European sea bass (Dicentrarchus labrax L.), of initial mass 5 g, were fed one of three practical type diets for 64 weeks. The three diets differed only in the added oil and were 100% fish oil (FO; diet A), 40% FO/60% vegetable oil blend (VO; diet B) where the VO blend was rapeseed oil, linseed oil and palm oil in the ratio 10/35/15 by weight and 40% FO/60% VO blend (diet C) where the ratio was 24/24/12 by weight. After final sample collection the remaining fish were switched to a 100% FO finishing diet for a further 20 weeks. After 64 weeks fish fed 60% VO diet B had significantly lower live mass and liver mass than fish fed diets A and C although SGR, FCR and length were not different between groups. There were no differences in any of the above parameters after either 14 or 20 weeks on the FO finishing diet. Fatty acid compositions of flesh were correlated to dietary fatty acids although there was selective retention of docosahexaenoic acid (22:6n-3; DHA) regardless of dietary input. Inclusion of dietary VO resulted in significantly reduced flesh levels of DHA and eicosapentaenoic acid (20:5n-3; EPA) while 18:1n-9, 18:2n-6 and 18:3n-3 were all significantly increased in fish fed the 60% VO diets. Fatty acid compositions of liver showed broadly similar changes, as a result of dietary fatty acid composition, as was seen in flesh. However, the response of flesh and liver to feeding a FO finishing diet was different. In flesh, DHA and EPA values were not restored after 14 or 20 weeks of feeding a FO finishing diet with the values in fish fed the two 60% VO diets being around 70% of the values seen in fish fed FO throughout. Conversely, and despite liver DHA and EPA levels being reduced to only 40% of the value seen in fish fed 100% FO after 64 weeks, the levels of liver DHA and EPA were not significantly different between treatments after feeding the FO finishing diet for 14 weeks. However, a 200 g portion of sea bass flesh, after feeding the experimental diets for 64 weeks followed by a FO diet for 14 weeks, contained 1.22 and 0.95 g of EPA + DHA for fish fed FO or 60% VO, respectively. Therefore, sea bass grown for most of the production cycle using diets containing 60% VO can still contribute a significant quantity of healthy n-3 HUFA to the human consumer.     

Fish oil supplementation of maternal rats on an n-3 fatty acid-deficient diet prevents depletion of maternal brain regional docosahexaenoic acid levels and has a postpartum anxiolytic effect

Docosahexaenoic acid (DHA) and arachidonic acid (AA) are the major polyunsaturated fatty acids (PUFA) in the neuronal membrane. Most DHA and AA accumulation in the brain occurs during the perinatal period via placenta and milk. This study examined whether maternal brain levels of DHA and AA are depleted during pregnancy and lactation due to meeting the high demand of the developing nervous system in the offspring and evaluated the effects of the reproductive cycle on serotonin metabolism and of fish oil (FO) on postpartum anxiety. Pregnant rats were fed during pregnancy and lactation with a sunflower oil-based n-3 PUFA-deficient diet without or with FO supplementation, which provided 0.37% of the energy source as n-3 PUFA, and the age-matched virgin rats were fed the same diets for 41 days. In both sets of postpartum rats, decreased DHA levels compared to those in virgin females were seen in the hypothalamus, hippocampus, frontal cortex, cerebellum, olfactory bulb and retina, while AA depletion was seen only in the hypothalamus, hippocampus and frontal cortex. Serotonin levels were decreased and turnover increased in the brainstem and frontal cortex in postpartum rats compared to virgin rats. FO supplementation during pregnancy and lactation prevented the decrease in maternal brain regional DHA levels, inhibited monoamine oxidase-A activity in the brainstem and decreased anxiety-like behavior. We propose that the reproductive cycle depletes maternal brain DHA levels and modulates maternal brain serotonin metabolism to cause postpartum anxiety and suggest that FO supplementation may be beneficial for postpartum anxiety in women on an n-3 PUFA-deficient diet.     

Effect of docosahexaenoic acid and ascorbate on peroxidation of retinal membranes of ODS rats

Mutant male osteogenic disorder Shionogi (ODS) rats, unable to synthesize ascorbic acid, were fed diets containing a high content of docosahexaenoic acid (DHA) and different amounts of ascorbic acid, to study the effect of DHA on peroxidative susceptibility of the retina and possible antioxidant action of ascorbic acid. ODS rats were fed from 7 weeks of age with diets containing high DHA (6.4% of total energy). A control group received a diet high in linoleic acid. The diets also contained varying amounts of ascorbic acid. Fatty acid compositions and phospholipid hydroperoxides in rod outer segment (ROS) membranes, and retinal ascorbic acid were analyzed. DHA in ROS membranes was significantly increased in rats fed high DHA, compared with the linoleic acid diet. Levels of phospholipid hydroperoxides in the DHA-fed rats were significantly higher than the linoleic acid-fed rats. Ascorbic acid supplementation did not suppress the phospholipid hydroperoxide levels after a high DHA diet, even when the supplement increased the content of retinal ascorbic acid. In conclusion, high DHA feeding induced a marked increase of phospholipid hydroperoxides in ROS membranes of ODS rats. Supplementation of ascorbic acid did not reverse this increase.     

N-3 polyunsaturated fatty acid consumption produces neurobiological effects associated with prevention of depression in rats after the forced swimming test

Epidemiological data and clinical trials suggest that n-3 polyunsaturated fatty acids (PUFA) eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have preventive and therapeutic effects on depression; however, the underlying mechanism remains elusive. The present study aimed to examine the behavioral effects and antidepressant mechanism of n-3 PUFA using a forced swimming test. Eleven-week-old male Sprague-Dawley rats were fed an American Institute of Nutrition-93M diet containing 0%, 0.5% or 1% EPA and DHA relative to the total energy intake in their diet for 12 weeks (n=8 per group). Total dietary intake, body weight and hippocampus weights were not significantly different among groups. The groups administered 0.5% and 1% EPA+DHA diets had significantly higher levels of n-3 PUFA in their brain phospholipids compared to those in the control group. The immobility time was significantly decreased and the climbing time was significantly increased in the 0.5% and 1% EPA+DHA groups compared with those in the 0% EPA+DHA group. Plasma serotonin concentration and hippocampus c-AMP response element binding protein (CREB) expression were significantly increased in the 0.5% and 1% EPA+DHA groups compared with those in the 0% EPA+DHA group. Conversely, interleukin (IL)-6 expression was significantly reduced in the 0.5% and 1% EPA+DHA groups compared with that in the 0% EPA+DHA group. However, there were no dose-dependent effects of n-3 PUFA and no significant differences in expressions of IL-1β, tumor necrosis factor-α, brain-derived neurotrophic factor or phosphorylated CREB. In conclusion, long-term intake of EPA+DHA induced antidepressant-like effects in rats and overexpression of CREB via decreased IL-6 expression.     

Exposure to a maternal n-3 fatty acid-deficient diet during brain development provokes excessive hypothalamic–pituitary–adrenal axis responses to stress and behavioral indices of depression and anxiety in male rat offspring later in life

Brain docosahexaenoic acid (DHA, 22:6n-3) accumulates rapidly during brain development and is essential for normal neurological function. The aim of this study was to evaluate whether brain development was the critical period in which DHA deficiency leads to dysregulation of the hypothalamic–pituitary–adrenal (HPA) axis in response to stress later in life. Rats were exposed to an n-3 fatty acid-deficient diet or the same diet supplemented with fish oil as an n-3 fatty acid-adequate diet either throughout the preweaning period from embryo to weaning at 3 weeks old or during the postweaning period from 3 to 10 weeks old. Exposure to the n-3 fatty acid-deficient diet during the preweaning period resulted, at weaning, in a significant decrease in hypothalamic DHA levels and a reduced male offspring body weight. DHA deficiency during the preweaning period significantly increased and prolonged restraint stress-induced changes in colonic temperature and serum corticosterone levels, caused a significant increase in GABA_A antagonist-induced heart rate changes and enhanced depressive-like behavior in the forced swimming test and anxiety-like behavior in the plus-maze test in later life. These effects were not seen in male rats fed the n-3 fatty acid-deficient diet during the postweaning period. These results suggest that brain development is the critical period in which DHA deficiency leads to excessive HPA responses to stress and elevated behavioral indices of depression and anxiety in adulthood. We propose that these effects of hypothalamic DHA deficiency during brain development may involve a GABA_A receptor-mediated mechanism.     

Effects of structured lipids containing eicosapentaenoic or docosahexaenoic acid and caprylic acid on serum and liver lipid profiles in rats

The physiological activity and effect on lipid metabolism of four types of structured lipids (SLs), that contain caprylic acid (C8) and either eicosapentaenoic (EPA) or docosahesaenoic acid (DHA), were evaluated in male Wistar rats fed experimental diets containing 7% (wt %) of each SL and 3% (wt %) soybean oil for 28 days. Control rats were fed a diet containing 10% (wt %) soybean oil. The relative perirenal adipose tissue weights of rats fed D-8-8 and 8-D-8 diets were significantly lower than those of other groups. We observed significantly lower serum cholesterol concentrations in rats fed SLs than those of control group over experimental period. The serum lipids concentrations in rats fed diets containing SLs were significantly lower P < 0.05) than those of soybean oil group. The fatty acid compositions of WAT did not reflect the structural differences in the triglyceride. These results suggest that the physiological effects of the SLs used in this study were due to the fatty acids rather than the structural specificity. Therefore, further study will be needed to ascertain the most desirable structural configuration.     

Improvement of nutritional quality of cultured sobaity sea bream,Sparidentex hasta (Valenciennes) muscle by preharvest feeding of finisher feeds

A 6‐month long study was conducted to improve the nutritional quality of the cultured sobaity bream, Sparidentex hasta by feeding them finisher feeds containing high docosahexaenoic acid (DHA) at the last two months of the grow‐out stage so that the muscle DHA level be increased at par to the wild. A grow‐out feed used from the beginning until the end of the trial was considered as the control (Diet 1). Experimental diets 2 and 3 were formulated to contain 9.0% DHA (e.g. 1.68 g DHA/100 g feed) and 10.5% DHA (2.20 g DHA/100 g feed), by incorporating high DHA tuna oil into a sea bream grow‐out diet. For comparison, a commercial finisher feed (Diet 4) from Skretting, Italy was also used. The results of this study demonstrated that fish fed DHA enriched finisher diets resulted in significantly (p < .05) better growth, feed utilization and higher muscle eicosapentaenoic acid (EPA) and DHA content compared to those fed grow‐out diet. The muscle DHA and EPA of fish fed finisher diets were also higher than those of the whole year average DHA and EPA content of wild sobaity. An organoleptic evaluation showed no significant (p > .05) differences between sensory attributes of muscle from cultured and wild sea bream. The results of the study demonstrated that feeding finisher feed enriched with DHA at the later part of the grow‐out operation, the n‐3 PUFA levels of cultured sobaity can cost‐effectively be increased at par to the wild.     

Dietary supplementation with docosahexaenoic acid,but not with eicosapentaenoic acid,reduces host resistance to fungal infection in mice

The effect of dietary docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) on host resistance to Paracoccidioides brasiliensis infection was investigated. Mice fed palm oil supplemented with DHA showed reduced antifungal activity in the spleen and liver, as compared with mice fed palm oil or soybean oil without supplementation with DHA. Mice fed DHA-supplemented soybean oil also showed reduced antifungal activity in the liver, but the extent of reduction was less profound. This reduction in antifungal activity was not observed with EPA-supplemented palm or EPA-supplemented soybean oil. These results suggest that two factors, DHA and palm oil in combination, are involved in reducing the host resistance. DHA-enriched palm oil was also responsible for an increase in DHA concentration and a marked decrease in arachidonic acid content in the spleen and liver. However, this group did not show elevated spleen and liver phospholipid hydroperoxide levels compared with the other groups, excluding the possibility that the reduction in antifungal activity observed with DHA-enriched palm oil is due to acceleration of in vivo lipid peroxidation. Greater infection-induced increases in spleen and serum interferon-gamma concentrations were observed in mice fed DHA-enriched palm oil compared with the other groups.     

Bio-availability and metabolism of n-3 fatty acid rich garden cress (Lepidium sativum) seed oil in albino rats

The ratio of fatty acids namely linoleic acid (LA, 18:2, n-6) and alpha linolenic acid (ALA, 18:3, n-3) in the diet plays an important role in enrichment of ALA in tissues and further conversion to long-chain polyunsaturated fatty acids (LC-PUFA) like eicosapentaenoic acid (EPA, 20:5, n-3) and docosahexaenoic acid (DHA, 22:6, n-3). Garden cress seed oil (GCO) is one of the richest sources of omega-3 fatty acid and contains 29-34.5% of ALA. In this study, dietary supplementation of GCO on bio-availability and metabolism of alpha-linolenic acid was investigated in growing rats. Male wistar rats were fed with semi-purified diets supplemented with 10.0% sunflower oil (SFO 10%); 2.5% GCO and 7.5% SFO (GCO 2.5%); 5% GCO and 5% SFO (GCO 5.0%); 10% GCO (GCO 10%) for a period of 8 weeks. There was no significant difference with regard to the food intake, body weight gain and organ weights of rats in different dietary groups. Rats fed with GCO showed significant increase in ALA levels in serum and tissues compared to SFO fed rats. Feeding rats with 10% GCO lowered hepatic cholesterol by 12.3% and serum triglycerides by 40.4% compared to SFO fed group. Very low density lipoprotein cholesterol (VLDL-C) and low density lipoprotein cholesterol (LDL-C) levels decreased by 9.45% in serum of 10% GCO fed rats, while HDL remained unchanged among GCO fed rats. Adipose tissue showed incorporation of 3.3-17.4% of ALA and correlated with incremental intake of ALA. Except in adipose tissue, the EPA, DHA levels increased significantly in serum, liver, heart and brain tissues in GCO fed rats. A maximum level of DHA was registered in brain (11.6%) and to lesser extent in serum and liver tissues. A significant decrease in LA and its metabolite arachidonic acid (AA) was observed in serum and liver tissue of rats fed on GCO. Significant improvement in n-6/n-3 fatty acid ratio was observed in GCO based diets compared to diet containing SFO. This is the first study to demonstrate that supplementation of GCO increases serum and liver ALA, EPA, DHA and decreases LA and AA in rats. Therefore, the GCO can be considered as a potential, alternate dietary source of ALA.     

Dietary eicosapentaenoic acid prevents systemic immunosuppression in mice induced by UVB radiation.

Moison, R. M. W. and Beijersbergen van Henegouwen, G. M. J. Dietary Eicosapentaenoic Acid Prevents Systemic Immunosuppression in Mice Induced by UVB Radiation. Radiat. Res. 156, 36-44 (2001).Reactive oxygen species (ROS) contribute to the immunosuppression induced by UVB radiation. Omega-3 fatty acids in fish oil, e.g. eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), can modulate immunoresponsiveness, but because of their susceptibility to ROS-induced damage, they can also challenge the epidermal antioxidant defense system. The influence of dietary supplementation with different omega-3 fatty acids on systemic immunosuppression induced in mice by UVB radiation was studied using the contact hypersensitivity response to trinitrochlorobenzene. In an attempt to study the mechanisms involved, UVB-radiation-induced changes in epidermal antioxidant status were also studied. Mice received high-fat (25% w/w) diets enriched with either oleic acid (control diet), EPA, DHA, or EPA + DHA (MaxEPA). Immunosuppression induced by UVB radiation was 53% in mice fed the oleic acid diet and 69% in mice fed the DHA diet. In contrast, immunosuppression was only 4% and 24% in mice fed the EPA and MaxEPA diets, respectively. Increased lipid peroxidation and decreased vitamin E levels (P < 0.05) were found in unirradiated mice fed the MaxEPA and DHA diets. For all diets, exposure to UVB radiation increased lipid peroxidation (P < 0.05), but levels of glutathione (P < 0.05) and vitamin C (P > 0.05) decreased only in the mice given fish oil. UVB irradiation did not influence vitamin E levels. In conclusion, dietary EPA, but not DHA, protects against UVB-radiation-induced immunosuppression in mice. The degree of protection appears to be related to the amount of EPA incorporated and the ability of the epidermis to maintain an adequate antioxidant level after irradiation.     

Dietary eicosapentaenoic acid and docosahexaenoic acid are linearly retained by common insect crop pests (cabbage looper and bertha armyworm) and alter insect biomass

The long-chain omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are prevalent in aquatic ecosystems and are not part of the natural diet of herbivorous, terrestrial insects, which generally consume alpha-linolenic acid (ALA) and linoleic acid (LNA). However, recent advances in genetic engineering have lead to the development of terrestrial crops that express the novel traits of EPA and DHA production. In the present study, we examine the effects of dietary EPA and DHA on the growth, development and fatty acid content of two crop pest insects: bertha armyworm and cabbage looper. Five experimental diets were formulated to include increasing amounts of pure EPA and DHA (in relation to the total diet lipid level), according to the ratios (EPA + DHA relative to a vegetable oil containing ALA and LNA): 0 (control), 0.25 : 0.75 (lowest), 0.5 : 0.5 (low), 0.75 : 0.25 (medium) and 1 : 0 (high). Dietary EPA and DHA had significant effects on development time, mass and fatty acid content in both species. Dietary treatment (interactive with time) had a significant effect on individual mass of both insects, indicating that, over time, EPA and DHA impacted growth. However, insect mass, development and morphology results are not linearly related with increasing dietary EPA and DHA. Both species retained EPA and DHA in adult form, and the body content of EPA and DHA was significantly, positively correlated with EPA and DHA diet treatments in both the bertha armyworm (r² = 91.3%) and cabbage looper (r² = 75.8%). Dietary EPA and DHA could have fitness consequences for these organisms and could be nutritionally transferred to higher consumers.