Inhibition of constitutive Akt (PKB) phosphorylation by docosahexaenoic acid in the human breast cancer cell line MDA-MB-453

Many breast cancer cells express aberrantly activated receptor tyrosine kinases and are associated with deregulated phosphorylation of Akt (PKB). They are also often associated with a high level of free monounsaturated (MUFA) and saturated (SFA) fatty acids. We studied the effect of DHA and other polyunsaturated fatty acids (PUFAs) on these anomalies in a human breast cancer cell line, MDA-MB-453. Inhibitors of the Akt T308 kinase (PDK1) or S473 kinase (mTORC2, DNA-dependent protein kinase and integrin-linked kinase) and combinations of two of them incompletely inhibited, or even enhanced, the phosphorylation in this cell line. In contrast, it was found that DHA as well as other PUFAs inhibited Akt phosphorylation on T308 after 24 h. These PUFAs also blocked phosphorylation of S473, although certain omega-6 PUFAs were ineffective. After 48 h, only DHA inhibited Akt phosphorylation on the both residues. DHA, and other PUFAs though less efficiently, also elevated the expression of a mitochondrial enzyme, 2,4-dienoyl-CoA reductase, which catalyzes process necessary for β-oxidation of PUFAs. These PUFAs were present in the cells at high concentrations and reduced the amount of free and phospholipid-bound MUFAs. DHA most efficiently blocked deregulated cell proliferation while the effects of other PUFAs were moderate. These results suggest that DHA suppressed the growth of the cancer cell through its specifically persistent block of Akt phosphorylation in conjunction with modulation of fatty acid metabolism.     

Dietary ratio of n-6/n-3 PUFAs and docosahexaenoic acid: actions on bone mineral and serum biomarkers in ovariectomized rats

Hypoestrogenic states escalate bone loss in animals and humans. This study evaluated the effects of the amount and ratio of dietary n-6 and n-3 polyunsaturated fatty acids (PUFAs) on bone mineral in 3-month-old sexually mature ovariectomized (OVX) Sprague-Dawley rats. For 12 weeks, the rats were fed either a high-PUFA (HP) or a low-PUFA (LP) diet with a ratio of n-6/n-3 PUFAs of 5:1 (HP5 and LP5) or 10:1 (HP10 and LP10). All diets (modified AIN-93G) provided 110.4 g/kg of fat from safflower oil and/or high-oleate safflower oil blended with n-3 PUFAs (DHASCO oil) as a source of docosahexaenoic acid (DHA). Fatty acid analyses confirmed that the dietary ratio of 5:1 significantly elevated the amount of DHA in the periosteum, marrow and cortical and trabecular bones of the femur. Dual-energy X-ray absorptiometry measurements for femur and tibia bone mineral content (BMC) and bone mineral density showed that the DHA-rich diets (HP5 and LP5) resulted in a significantly lower bone loss among the OVX rats at 12 weeks. Rats fed the LP diets displayed the lowest overall serum concentrations of the bone resorption biomarkers pyridinoline (Pyd) and deoxypyridinoline, whereas the bone formation marker osteocalcin was lowest in the HP groups. Regardless of the dietary PUFA content, DHA in the 5:1 diets (HP5 and LP5) preserved rat femur BMC in the absence of estrogen. This study indicates that the dietary ratio of n-6/n-3 PUFAs (LP5 and HP5) and bone tissue concentration of total long-chain n-3 PUFAs (DHA) minimize femur bone loss as evidenced by a higher BMC in OVX rats. These findings show that dietary DHA lowers the ratio of 18:2n-6 (linoleic acid)/n-3 in bone compartments and that this ratio in tissue correlates with reduced Pyd but higher bone alkaline phosphatase activity and BMC values that favor bone conservation in OVX rats.     

Eicosapentaenoic acid and docosahexaenoic acid modulate MAP kinase enzyme activity in human T-cells

In order to investigate the implication of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) in T signalling, we assessed their effects on the activation of two mitogen activated protein (MAP) kinases, i.e. extracellularly-regulated kinases 1 and 2 (ERK1/ERK2) in Jurkat T-cells. The n-3 polyunsaturated fatty acids (PUFAs) alone failed to induce MAP kinase (MAPK) enzyme activity. To elucidate whether DHA and EPA act via protein kinase C (PKC) dependent and independent pathways, we employed their respective activators, i.e. phorbol 12-myristate 13-acetate (PMA) and antiCD3 antibodies. We observed that U0126, an inhibitor of MAPK kinase-ERK kinase 1/2 (MEK1/2), abolished the actions of these two agents on MAPK activation, suggesting that they act upstream of MEK1/2. Further EPA and DHA diminished both the PMA- and antiCD3 antibodies-induced enzyme activity of ERK1/ERK2 in Jurkat T-cells. Interestingly, okadaic acid (OA), a phosphatase inhibitor seems to act downstream of MEK1/2 as U0126 failed to inhibit the OA-induced MAPK activation. It is noteworthy that EPA and DHA not only failed to curtail the OA-induced MAPK activity but also these n-3 PUFAs at 20 M potentiated the action of OA. Therefore, EPA and DHA seem to modulate MAPK activation upstream and downstream of MEK1/2. On the hand, arachidonic acid, an n-6 PUFA potentiated the MAPK enzyme activity. In conclusion, our study shows that EPA and DHA may regulate T-cells functions by modulating MAPK enzyme activity.     

裂殖壶藻藻油DHA对高脂饮食诱导肥胖小鼠的影响

【目的】肥胖症是一种慢性代谢类疾病,具有较高的发病率和高危后果。研究表明,n-3多不饱和脂肪酸(n-3 Polyunsaturated fatty acids,n-3 PUFAs),特别是二十二碳六烯酸(Docosahexaenoic acid,DHA)对与肥胖症相关疾病有较好的防治效果,对体内脂质代谢有重要的调节作用。探讨裂殖壶藻(Schizochytrium sp.)藻油DHA对高脂饮食诱导肥胖小鼠体重、脂肪组织重量、血脂、肝和脂肪组织病理形态和脂质代谢相关基因表达的影响。【方法】通过高脂饮食建立小鼠肥胖模型,以体重增幅15%为标准分出肥胖小鼠。试验共分五组:(1)低脂对照组;(2)高脂模型组;(3)高脂+低剂量藻油组(50 mg DHA/kg);(4)高脂+中剂量藻油组(100 mg DHA/kg);(5)高脂+高剂量藻油组(200 mg DHA/kg)。其中,藻油处理组灌服相应剂量藻油,低脂对照组和高脂模型组灌胃同等体积玉米油。处理9周后,腹腔麻醉,摘眼球取血并分离血清,测血清中甘油三酯、胆固醇和高密度脂蛋白含量;之后处死小鼠,分离附睾、肾周和肠系膜脂肪组织及肝脏,称湿重;附睾脂肪和肝组织切片进行HE染色,观察病理变化情况;利用RT-PCR检测附睾脂肪组织中激素敏感脂酶(Hormone sensitive lipase,HSL)基因的m RNA表达情况。【结果】藻油处理组小鼠体重没有显著下降,但是腹部脂肪重量显著降低、脂肪细胞体积明显小于高脂模型组;同时血清中甘油三酯、胆固醇含量显著降低,肝组织异位脂肪堆积明显减少;脂肪组织中HSL基因的表达水平显著提高。【结论】裂殖壶藻藻油DHA处理能显著降低高脂饮食导致的小鼠腹部脂肪积累并改善血脂,可能有利于肥胖症的防治。     

Mechanisms by which docosahexaenoic acid and related fatty acids reduce colon cancer risk and inflammatory disorders of the intestine

A growing body of epidemiological, clinical, and experimental evidence has underscored both the pharmacological potential and the nutritional value of dietary fish oil enriched in very long chain n − 3 PUFAs such as docosahexaenoic acid (DHA, 22:6, n − 3) and eicosapentaenoic acid (EPA, 20:5, n − 3). The broad health benefits of very long chain n − 3 PUFAs and the pleiotropic effects of dietary fish oil and DHA have been proposed to involve alterations in membrane structure and function, eicosanoid metabolism, gene expression and the formation of lipid peroxidation products, although a comprehensive understanding of the mechanisms of action has yet to be elucidated. In this review, we present data demonstrating that DHA selectively modulates the subcellular localization of lipidated signaling proteins depending on their transport pathway, which may be universally applied to other lipidated protein trafficking. An interesting possibility raised by the current observations is that lipidated proteins may exhibit different subcellular distribution profiles in various tissues, which contain a distinct membrane lipid composition. In addition, the current findings clearly indicate that subcellular localization of proteins with a certain trafficking pathway can be subjected to selective regulation by dietary manipulation. This form of regulated plasma membrane targeting of a select subset of upstream signaling proteins may provide cells with the flexibility to coordinate the arrangement of signaling translators on the cell surface. Ultimately, this may allow organ systems such as the colon to optimally decode, respond, and adapt to the vagaries of an ever-changing extracellular environment.     

Incorporation of eicosapentaenoic and docosahexaenoic acids by a yeast (FO726A)

An eicosapentaenoic acid (EPA)- and docosahexaenoic acid (DHA)-incorporating yeast, FO726A, was putatively identified as Candida guilliermondii on the basis of morphological, physiological and biochemical characteristics. Culture conditions for FO726A were investigated with respect to cell mass productivity, cellular accumulation of total lipid, triglyceride (TG), EPA and DHA. When grown at 20 degrees C for 24 h in an optimal medium containing 1 g scrap fish oil, the yeast yielded 820 mg dry cells which consisted of 40.7% lipid, 40.2% protein and 14.1% carbohydrate. The lipid (334mg) consisted of 300 mg TG (36.6% of dry cells), 23.2 mg EPA (2.8%) and 54.8 mg DHA (6.7%), and the recovery rates of EPA and DHA from the fish oil were 27.1 and 43.6%, respectively. The positional distributions of fatty acids in the TG from the yeast were then investigated and compared with those in the TG from the fish oil. The EPA and DHA in the fish oil were concentrated more in the sn-1,3 positions (8.8 and 13.7%, respectively) than in the sn-2 position (3.7 and 10.8%, respectively). In the case of the TG from the yeast, EPA was present to a greater extent in the sn-1,3 positions than in the sn-2 position. In contrast, DHA was preferentially present in the sn-2 position, approximately twice that in the sn-1,3 positions.     

Differential roles of internal and terminal double bonds in docosahexaenoic acid: Comparative study of cytotoxicity of polyunsaturated fatty acids to HT-29 human colorectal tumor cell line

The role of the double bonds in docosahexaenoic acid (22:6(Δ4,7,10,13,16,19); DHA) in cytotoxic lipid peroxidation was studied in a superoxide dismutase-defective human colorectal tumor cell line, HT-29. In a conventional culture, DHA and other polyunsaturated fatty acids (PUFAs) were found to induce acute lipid peroxidation and subsequent cell death. PUFAs that lack one or both the terminal double bonds (Δ19 and Δ4) but share Δ7,10,13,16 such as 22:5(Δ7,10,13,16,19), 22:5(Δ4,7,10,13,16), and 22:4(Δ7,10,13,16) were more effective than DHA. Lipid peroxidation and cell death were completely inhibited, except by 22:4(Δ7,10,13,16) when radical-mediated reactions were suppressed by culturing cells in 2% O(2) in the presence of vitamin E. DHA and C22:5 PUFAs but not 22:4(Δ7,10,13,16) were efficiently incorporated in phosphatidylinositol, regardless of the culturing conditions. These and other results suggested that the internal unsaturations Δ7,10,13,16 were sensitive to lipid peroxidation, whereas the terminal ones Δ19 and Δ4 appeared to be involved in assimilation into phospholipids.     

Eicosapentaenoic acid and docosahexaenoic acid effects on tumour mitochondrial metabolism, acyl CoA metabolism and cell proliferation

In order to investigate the effects of high-fat diets rich in eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), Wistar rats bearing subcutaneous implants of the Walker 256 tumour were fed pelleted chow containing low DHA/EPA or high DHA/EPA. The presence of n-3 polyunsaturated fatty acids (PUFAs) led to a marked suppression (35-46%) of tumour growth over a 12 day period. Both the whole tumour homogenate and the Percoll-purified mitochondrial fraction presented significant changes in fatty acid composition. The levels of EPA increased in both n-3 dietary groups while the levels of DHA increased only in the high DHA/EPA group, in comparison with the control chow-fed group. The presence of n-3 PUFAs led to an increase in mitochondrial acyl CoA synthetase activity, but neither the cytoplasmic acyl CoA content nor the n-3 fatty acid composition of the cytoplasmic acyl CoAs was altered by the diet. The content of thiobarbituric acid-reactive substances (TBARS) was increased in the low DHA/EPA group but was unchanged in the high DHA/EPA group. In vitro studies with the Walker 256 cell line showed a 46% decrease in cell growth in the presence of either EPA or DHA which was accompanied by a large decrease in the measured mitochondrial membrane potential. The TBARS content was increased only in the EPA-exposed cells. Cell cycle analysis identified a decrease in G0-G1 phase cells and an increase in G2-M phase cells and apoptotic cells, for both EPA and DHA-exposed cells. The data show that the presence of n-3 PUFAs in the diet is able to significantly after the growth rate of the Walker 256 tumour. The involvement of changes in mitochondrial membrane composition and membrane potential have been indicated for both EPA and DHA, while changes in lipid peroxidation have been identified in the presence of EPA but not of DHA.     

A modified <Emphasis Type="Italic">n</Emphasis>–3 fatty acid desaturase gene from <Emphasis Type="Italic">Caenorhabditis briggsae</Emphasis> produced high proportion of DHA and DPA in transgenic mice

The functions of polyunsaturated fatty acids (PUFAs) have been widely investigated. In mammals, levels of n-3 PUFAs are relatively low compared to those of n-6 PUFAs. Either a lack of n-3 PUFAs or an excess of n-6 PUFAs could potentially cause health problems in humans. Hence, methods to increase the amount of n-3 PUFAs in diet have been intensely sought. In this study, we demonstrated that the n-3 fatty acid desaturase gene (sFat-1) synthesized from revised and optimized codons based on roundworm Caenorhabditis briggsae genomic gene for enhanced expression in mammals was successfully expressed in Chinese hamster ovary (CHO) cells and significantly elevated cellular n-3 PUFA contents. We generated sFat-1 transgenic mice by introducing mammal expression vector DNAs containing the sFat-1 gene into regular mice through the method of microinjection. Fatty acid compositions were then altered and the levels of docosahexaenoic acid (DHA, 22:6n-3) and docosapentaenoic acid (DPA, 22:5n-3) were greatly increased in these transgenic mice. Various types of tissues in the transgenic mice produced many types of n-3 PUFAs, such as alpha-linolenic acid (ALA; 18:3n-3), eicosapentaenoic acid (EPA, 20:5n-3), DPA, and DHA, for example, muscle tissues of the transgenic mice contained 12.2% DHA, 2.0% DPA, and 23.1% total n-3 PUFAs. These research results demonstrated that the synthesized sFat-1 gene with modified and optimized codons from C. briggsae possess functional activity and greater capability of producing n-3 PUFAs, especially DHA and DPA, in transgenic mice.     

Effect of arachidonic, eicosapentaenoic and docosahexaenoic acids on the oxidative status of C6 glioma cells

n-3 polyunsaturated fatty acids (PUFAs) have been described to have beneficial effects on brain development and in the prevention and treatment of brain damage. C6 glioma cells were incubated with 100 microM of either C20:4n-6 (ARA), or C20:5n-3 (EPA), or C22:6n-3 (DHA) for different time periods to assess whether these acids altered the cellular oxidative state. The ARA and EPA were promptly metabolised to C22:4n-6 and C22:5n-3, respectively, whereas DHA treatment simply increased the amount of DHA in the cells. Cell viability was not affected by ARA, while a cytotoxic effect was observed 72 h after n-3 PUFAs supplementation. The levels of reactive oxygen species and thiobarbituric acid-reactive substances were significantly higher in DHA-treated cells than in EPA- and ARA-treated groups. This modification in the oxidative cellular status was also highlighted by a significant increase in catalase activity and a decrease in glutathione content in DHA-supplemented cells. Glucose-6-phosphate dehydrogenase activity, an enzyme involved in redox regulation, and O2*- release were significantly increased both in EPA and DHA groups. The effect of DHA was more severe than that of EPA. No significant changes were observed in the ARA group with respect to untreated cells. These data show that EPA and DHA induce alterations in the oxidative status that could affect the glial function.     

Membrane fluidity changes are associated with the antiarrhythmic effects of docosahexaenoic acid in adult rat cardiomyocytes

Previous studies using neonatal rat cardiomyocytes have reported antiarrhythmic effects of long-chain polyunsaturated fatty acids (PUFAs). In this study, we examined the effects of the n-3 polyunsaturated fatty acid docosahexaenoic acid (DHA) on the spontaneous contractile activity and membrane fluidity of adult rat ventricular myocytes. Cardiomyocytes were induced to contract spontaneously by continuous superfusion of a solution containing the arrhythmogenic agents isoproterenol (a beta-adrenergic receptor agonist) or lysophosphatidylcholine. The percentage of cardiomyocytes displaying spontaneous contractions induced by isoproterenol when pretreated with the saturated fatty acid docosanoic acid was 48.1 +/- 7.7%; the percentage for cardiomyocytes pretreated with DHA was 7.1 +/- 2.4% (P < 0.01). DHA significantly prevented lysophosphatidylcholine-induced spontaneous contractions (17.7 +/- 6.5%) compared with treatment with the saturated fatty acid stearic acid (78.0 +/- 7.3%, P < 0.01). The membrane fluidizing agent benzyl alcohol also significantly prevented spontaneous contractions in cardiomyocytes. Membrane fluidity was determined by steady-state fluorescence anisotropy (r(ss)) using the fluorescent probe N-((4-(6-phenyl-1,3,5-hexatrienyl)phenyl)propyl) trimethyl-ammonium p-toluene-sulfonate (TMAP-DPH). DHA and benzyl alcohol dose-dependently decreased the r(ss); however, saturated fatty acids were without effect. These results suggest that the antiarrhythmic mechanisms of the n-3 PUFAs such as DHA may involve changes in membrane fluidity.     

Effects of docosahexaenoic acid on calcium pathway in adult rat cardiomyocytes

In this study we examined the effect of polyunsaturated fatty acids (PUFAs), in particular of docosahexaenoic acid (DHA), on calcium homeostasis in isolated adult rat cardiomyocytes exposed to KCl, ET-1 and anoxia. Free [Ca(2+)](i) in rat cardiomyocytes was 135.7 +/- 0.5 nM. Exposure to 50 mM KCl or 100 nM ET-1 resulted in a rise in free [Ca(2+)](i) in freshly isolated cells (465.4 +/- 15.6 nM and 311.3 +/- 12.6 nM, respectively) and in cultured cells (450.8 +/- 14.8 nM and 323.5 +/- 14.8 nM respectively). An acute treatment (20 minutes) with 10 microM DHA significantly reduced the KCl- and ET-1-induced [Ca(2+)](i) increase (300.9 +/- 18.1 nM and 232.08 +/- 11.8 nM, respectively). This reduction was greater after chronic treatment with DHA (72 h; 257.7 +/- 13.08 nM and 192.18 +/- 9.8 nM, respectively). Rat cardiomyocytes exposed to a 20 minute superfusion with anoxic solution, obtained by replacing O(2) with N(2) in gas mixture, showed a massive increase in cytosolic calcium (1200.2 +/- 50.2 nM). Longer exposure to anoxia induced hypercontraction and later death of rat cardiomyocytes. Preincubation with DHA reduced the anoxic effect on [Ca(2+)](i) (498.4 +/- 7.3 nM in acute and 200.2 +/- 12.2 nM in chronic treatment). In anoxic conditions 50 mM KCl and 100 nM ET-1 produced extreme and unmeasurable increases of [Ca(2+)](i.) Preincubation for 20 minutes with DHA reduced this phenomenon (856.1 +/- 20.3 nM and 782.3 +/- 7.6 nM, respectively). This reduction is more evident after a chronic treatment with DHA (257.7 +/- 10.6 nM and 232.2 +/- 12.5 nM, respectively). We conclude that in rat cardiomyocytes KCl, ET-1 and anoxia interfered with intracellular calcium concentrations by either modifying calcium levels or impairing calcium homeostasis. Acute, and especially chronic, DHA administration markedly reduced the damage induced by calcium overload in those cells.     

Fatty Acid Composition of Porcine Muscle and Adipose Tissue Lipids as Affected by Anatomical Location and Cod Liver Oil Supplementation of the Diet

In pigs fed a standard pig mash the contents of polyunsaturated fatty acids (PUFAs) of both the n-6 and n-3 series were significantly higher in the dark red mm adductores compared to the light coloured m longissimus lumborum. Perirenal fat had a higher concentration of saturated fatty acids (14:0,16:0, 18:0) than backfat, and a lower concentration of monounsaturated fatty acids, such as 16:ln-7 and 18:ln-9. Daily supplementation of 50 ml cod liver oil, rich in n-3 PUFAs, during the fourth and third week before slaughter led to a 1.4 to 1.7 times increase in the contents of n-3 PUFAs in muscles and fat depots. There was no difference between the incorporation of n-3 PUFAs in dark and light muscles. Perirenal fat contained more 20:5n-3 (EPA) and 22:6n-3 (DHA), but less 20:ln-9 (eicosenoic acid) than the backfat, after cod liver oil supplementation rich in these 3 fatty acids. Supplementation of cod liver oil reduced the n-6/n-3 fatty acid ratio in all anatomical locations examined.     

Dietary docosahexaenoic acid alters pregnant rat reproductive tissue prostaglandin and matrix metalloproteinase production

Shortened gestation is a major cause of infant mortality and morbidity. Evidence from both human and animal studies suggests that essential fatty acids of the n-6 and n-3 series play important and modifiable roles in gestational duration. We examined the influence of linolenic acid (LnA) vs. docosahexaenoic acid (DHA) on rat reproductive tissue prostaglandin (PG) and matrix metalloproteinase (MMP) indices of gestational duration. By varying the oil source of the diet, AIN-93G diets were constructed to provide either 0.7 energy % (en%) LnA, the current US intake of n-3 fatty acids, or 0.7 en% DHA. In addition, enhanced levels of 2.0 en% LnA or 2.0 e% DHA diets were also constructed. All diets contained approximately 6.0 en% linoleic acid (LA), the current US intake of LA. Four groups of 10 female rats were time-mated and fed the respective diets from conception through Day 20 of gestation. Day 20 uterus and placenta DHA were significantly increased by 160-180% by the 0.7 en% DHA diet, and by 250-350% by the 2.0 en% DHA diets in comparison to 0.7 en% LnA diet. DHA diets also significantly reduced uterus and placenta arachidonic acid content. Day 20 placenta and uterus PGE(2) and placenta PGF(2alpha) production rates were significantly reduced by 27-47% in the 0.7 en% DHA group in comparison to 0.7 en% LnA. Increasing LnA to 2.0 en% was without effect. Providing DHA at the enhanced 2.0 en% did not significantly enhance the suppression of PG production. Placenta active MMP-2 and active MMP-9 (gelatinase) production was suppressed significantly by 30-43% in the 0.7 en% DHA group in comparison to the 0.7 en% LnA group, and 2.0 en% DHA did not enhance this suppression. Placenta collagenase activity comprising the sum of MMP-1, MMP-8 and MMP-13 was also suppressed by 60% in the 0.7 en% DHA diet group with no additional effect with 2.0 en% DHA provision. These results suggest that substituting DHA for LnA even at the current US n-3 fatty acid intake of 0.7 en% is effective in suppressing indices of premature delivery and shortened gestation. Increasing LnA intake by 3-fold to 2.0 en% is not effective. The form of dietary n-3 fatty acid, DHA vs. LnA, appears to be more important than the amount.     

Is the fatty acid composition of Daphnia galeata determined by the fatty acid composition of the ingested diet?

1. The fatty acid (FA) composition of Daphnia galeata and their algal food was analysed and showed many similarities, however, some significant differences were also found in the relative abundance of the FA C16 : 4ω3 and docosahexaenoic acid (DHA). Their relative abundances were much lower in daphnids than in their algal diet.
2. When daphnids were fed three distinct emulsion particles with DHA : eicosapentaenoic acid (EPA) ratios of c. 0.7, 2 and 4, the final DHA : EPA ratio in the daphnids always favoured EPA. The increase of the food DHA : EPA ratio resulted in a minor increase of DHA (to c. 2%). Feeding the animals on emulsion particles with increasing ratios of DHA : EPA, caused a minor ( c. 2%) increase of DHA level but EPA levels remained high ( c. 10%).
3. When labelled with [¹⁴C]linoleic acid and [¹⁴C]linolenic acid daphnids showed low conversion of both essential FA into C20 polyunsaturated fatty acids (PUFAs). This low conversion activity might explain the importance of C20 PUFAs as dietary compounds in the food of Daphnia.
4. The results indicate the insignificance of DHA and C16 : 4ω3 for daphnids. As EPA can be derived from C18 : 3ω3 it is not strictly essential, although it might be a significant factor in food quality for Daphnia.     

Rat heart cannot synthesize docosahexaenoic acid from circulating alpha-linolenic acid because it lacks elongase-2

The extent to which the heart can convert alpha-linolenic acid (alpha-LNA, 18:3n-3) to longer chain n-3 PUFAs is not known. Conversion rates can be measured in vivo using radiolabeled alpha-LNA and a kinetic fatty acid model. [1-(14)C]alpha-LNA was infused intravenously for 5 min in unanesthetized rats that had been fed an n-3 PUFA-adequate [4.6% alpha-LNA, no docosahexaenoic acid (DHA, 22:6n-3)] or n-3 PUFA-deficient diet (0.2% alpha-LNA, nor DHA) for 15 weeks after weaning. Arterial plasma was sampled, as was the heart after high-energy microwaving. Rates of conversion of alpha-LNA to longer chain n-3 PUFAs were low, and DHA was not synthesized at all in the heart. Most alpha-LNA within the heart had been beta-oxidized. In deprived compared with adequate rats, DHA concentrations in plasma and heart were both reduced by >90%, whereas heart and plasma levels of docosapentaenoic acid (DPAn-6, 22:5n-6) were elevated. Dietary deprivation did not affect cardiac mRNA levels of elongase-5 or desaturases Delta6 and Delta5, but elongase-2 mRNA could not be detected. In summary, the rat heart does not synthesize DHA from alpha-LNA, owing to the absence of elongase-2, but must obtain its DHA entirely from plasma. Dietary n-3 PUFA deprivation markedly reduces heart DHA and increases heart DPAn-6, which may make the heart vulnerable to different insults.     

Suppression of platelet-activating factor generation and modulation of arachidonate metabolism by dietary enrichment with (n-9) eicosatrienoic acid or docosahexaenoic acid in mouse peritoneal cells

Several studies have shown that dietary n-3 polyunsaturated fatty acids (PUFAs) suppress platelet-activating factor (PAF) generation in leukocytes of humans and rodents, which is associated with the antagonism of arachidonic acid metabolism. Dietary eicosatrienoic acid (20:3n-9, ETrA) is also suggested to antagonize arachidonic acid (AA) metabolism, but its effect on PAF generation in leukocytes has not been defined. In the present study, we investigated the effects of an ETrA-rich diet on PAF generation and AA metabolism in mouse peritoneal cells, which were compared with those of a docosahexaenoic acid (DHA)-rich diet. Mice were fed a diet supplemented with a lipid preparation rich in ETrA, a DHA-rich fish oil (FO) or palm oil (PO) for 3 weeks, and peritoneal cells containing more than 80% of monocytes/macrophages were obtained. The peritoneal cells in the DHA and ETrA diet groups generated upon zymosan stimulation a smaller amount of PAF than cells in the PO diet group. In the peritoneal cells of the DHA diet group, AA contents in phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were significantly lower than those in cells of the PO diet group, but those in phosphatidylinositol (PI) were not significantly different between the two dietary groups. A considerable amount of ETrA was incorporated into the peritoneal cells of the ETrA diet group, and AA was reduced as compared with the PO diet group. These changes occurred preferentially in PI but to a less extent in PC and PE. The amount of free AA released by the peritoneal cells upon zymosan stimulation was significantly reduced in the DHA diet group as compared with that in the PO diet group, whereas AA release was similar between the PO and ETrA diet groups. In conclusion, the effects of dietary ETrA on AA content in the phospholipid subclasses and AA release were quite different from those of dietary DHA, although both diets suppressed PAF generation in mouse peritoneal cells to a similar extent.