A new prostaglandin, C22-PGF4 alpha, synthesized from docosahexaenoic acid (C22:6n3) by trout gill

Omega-3 fatty acids and rodent behavior

This paper reviews the role of the n-3 fatty acids in the regulation of cognitive functions, locomotor and exploratory activity and emotional status in rodents. There are disparate data on the performance of n-3 fatty acid deficient animals in the open field test and elevated plus maze. Results obtained in our laboratory indicated slower habituation to the open field in deficient mice, which affects total locomotor and exploratory parameters. We also observed no change in plus maze performance of deficient mice under low-stress but elevated anxiety under high-stress conditions. There is some evidence of elevated aggression and increased immobility time in the forced swimming test caused by n-3 fatty acid deficiency in rodents. Effects of n-3 fatty acid deficiency and supplementation on learning in several tests such as the Morris water maze, two odor olfactory discriminations, radial arm maze performance and avoidance tasks are reviewed in detail. There is some evidence of an enhanced vulnerability to stress of n-3 fatty acid deficient animals and this factor can influence performance in a variety of tests. Thus, behavioral tasks that involve a higher level of stress may better differentiate behavioral effects related to brain docosahexaenoic acid (DHA) status. It is suggested that a fruitful area for future investigations of functional alterations related to brain DHA status will be the delineation of the factors underlying changes in performance in behavioral tasks. The possible role of non-cognitive factors like emotionality and attention in the impaired performance of n-3 fatty acid deficient animals also requires further investigation.

Distinguishing levuglandins produced through the cyclooxygenase and isoprostane pathways

The cyclooxygenase (COX) pathway generates enantiomerically pure levuglandin (LG) E(2) by a rearrangement of the prostaglandin (PG) endoperoxide PGH(2). The isoprostane pathway generates racemic LGE(2) together with stereoisomers, designated collectively as isoLGE(2), through free radical-induced lipid oxidation. Within seconds, both LGs and isoLGs are rapidly sequestered by protein adduction. In theory, the diastereomeric purity of LGE(2)-protein adduct-derived lysyl lactams can reveal the relative contributions of the COX and isoprostane pathways to LGE(2) stereoisomer production in vivo. Notably, however, the detection of LGE(2)-protein adducts does not provide a basis for inferring their formation through the isoprostane pathway in vivo unless the COX pathway can be rigorously excluded. In contrast, LGE(2)structural isomers, designated collectively as iso[n]LGE(2)s, are produced exclusively through the isoprostane pathway. Immunoassays that selectively recognize iso[n]LGE(2)-protein adducts are the only tools available to unambiguously detect and quantify the production of isolevuglandins in vivo through free radical-induced oxidation of arachidonates.

Levuglandins and isolevuglandins: stealthy toxins of oxidative injury

Inspired by a reaction discovered through basic research on the chemistry of the bicyclic peroxide nucleus of the prostaglandin endoperoxide PGH2, we postulated that levulinaldehyde derivatives with prostaglandin side chains, levuglandins (LGs), and structurally isomeric analogues, isolevuglandins (iso[n]LGs), would be generated by nonenzymatic rearrangements of prostanoid and isoprostanoid endoperoxides. Two decades of subsequent studies culminated in our discoveries of the LG and isoLG pathways, branches of the cyclooxygenase and isoprostane pathways, respectively. In cells, PGH2 rearranges nonenzymatically to LGs even in the presence of enzymes that use PGH2 as a substrate. IsoLGs, also known as isoketals or neuroketals, are generated in vivo through free radical-induced autoxidation of polyunsaturated phospholipid esters. Hydrolysis occurs after rapid adduction of isoLG phospholipids to proteins. The proclivity of these reactive species to avidly bind covalently with and cross-link proteins and nucleic acids complicated the hunt for LGs and isoLGs in vivo. The extraordinary reactivity of these "stealthy toxins" underlies much, if not all, of the biological consequences of LG and isoLG generation. They interfere with protein function and are among the most potent neurotoxic products of lipid oxidation known. Because they can accumulate over the lifetimes of proteins, iso[n]LG-protein adducts represent a convenient dosimeter of oxidative stress.

Mechanisms of action of docosahexaenoic acid in the nervous system

This review describes (from both the animal and human literature) the biological consequences of losses in nervous system docosahexaenoate (DHA). It then concentrates on biological mechanisms that may serve to explain changes in brain and retinal function. Brief consideration is given to actions of DHA as a nonesterified fatty acid and as a docosanoid or other bioactive molecule. The role of DHA-phospholipids in regulating G-protein signaling is presented in the context of studies with rhodopsin. It is clear that the visual pigment responds to the degree of unsaturation of the membrane lipids. At the cell biological level, DHA is shown to have a protective role in a cell culture model of apoptosis in relation to its effects in increasing cellular phosphatidylserine (PS); also, the loss of DHA leads to a loss in PS. Thus, through its effects on PS, DHA may play an important role in the regulation of cell signaling and in cell proliferation. Finally, progress has been made recently in nuclear magnetic resonance studies to delineate differences in molecular structure and order in biomembranes due to subtle changes in the degree of phospholipid unsaturation.

Prostaglandins in the kidney, urinary bladder and gills of the rainbow trout and European eel adapted to fresh water and seawater

Prostaglandins in kidney, gills, and urinary bladder of freshwater-adapted and seawater-adapted rainbow trout, Oncorhynchus mykiss (= Salmo gairdneri), and European eel, Anguilla anguilla, were determined by solid-phase extraction of tissue homogenates and high-pressure liquid chromatography. Prostaglandins E2, E1, F1 alpha, F2 alpha, and D2 and the more stable metabolite of prostacyclin, 6-keto F1 alpha, occurred in these osmoregulatory tissues. In gill filaments and kidneys of both eel and trout, prostaglandins D2 and 6-keto F1 alpha were major prostaglandins. Concentrations of these prostaglandins were significantly lower in the eel after seawater adaptation, but not in the trout. The urinary bladder of the trout contained the highest levels of prostaglandins; bladders of seawater-adapted trout contained prostaglandin D2 at 6.7 ng/mg wet tissue, the highest level of any prostaglandin determined in the present studies. Prostaglandin D2 was not detected in bladders of freshwater-adapted trout.

Antidiuretic and cardiovascular actions of prostaglandin E2 in the rainbow trout Salmo gairdneri

The renal and cardiovascular actions of intravenous injection or infusion of prostaglandin E2 (PGE2) have been investigated in the anaesthetised rainbow trout, Salmo gairdneri. Amounts of 1-2500 ng PGE2/kg body wt had a potent vasodilatory action and caused rapid dose-related decreases in dorsal aortic blood pressure. Intravenous infusion of PGE2 was associated with a secondary tachycardia and vasoconstriction. Injection of PGE2 resulted in transient dose-related decreases of urine production. Infusion of PGE2 at 200 ng/min/kg rapidly decreased glomerular filtration rates by reducing the populations of filtering nephrons and later by increasing the renal tubular water reabsorption. The possible endocrine systems which may be involved in the renal responses to PGE2 are discussed.

Lipoxygenase in trout gill tissue acting on arachidonic, eicosapentaenoic and docosahexaenoic acids

Lipoxygenase activity was characterized in the gill tissue of fresh-water trout. Incubation of arachidonic acid with gill preparations yielded 12-hydroxyeicosatetraenoic acid as the major product, suggesting a 12-lipoxygenase. Eicosapentaenoic acid was similarly converted to the 12-hydroxyeicosapentaenoic acid. Both arachidonic acid and docosahexaenoic acid were converted with equal apparent velocities and affinities into single monohydroxy derivatives. Analyses of the hydroxy product of docosahexaenoic acid were consistent with 14-hydroxydocosahexaenoic acid. This enzyme activity was localized to the cytosolic fraction and displayed a broad pH optimum around pH 7. The enzyme was insensitive to the cyclooxygenase inhibitors indomethacin and aspirin but activity was strongly inhibited in the presence of the lipoxygenase inhibitors, SnCl2 (5 mM), esculetin (10 microM) and eicosatetraynoic acid (100 microM).

The role of polyunsaturated fatty acids in fish

The physical properties of polyunsaturated and saturated fatty acids are compared in relation to melting points and fluidity. The role of polyunsaturated fatty acids on membrane fluidity and membrane bound enzyme activity is discussed. The influence of the environment, particularly temperature, on poikilothermic animals is considered in relation to membrane fatty acid composition and metabolism. The metabolic role of polyunsaturated fatty acids of the (n-3) series and their interaction with arachidonate metabolism is discussed.

Prostaglandin synthesis in goldfish heart, Carassius auratus

Potential precursors for prostaglandin (PG) synthesis were measured in goldfish heart and skeletal muscle by gas chromatography. Heart tissue contained docosahexaenoic, arachidonic, eicosapentaenoic, and eicosatrienoic acids in concentrations of 3223 +/- 128, 1216 +/- 7.8, 260 +/- 72.8, and 250 +/- 14 ng/mg wet wt, respectively. 14C-Labeled substrates were examined for their ability to be converted to prostaglandins. Eicosatrienoic and docosahexaenoic acid were not synthesized into prostaglandins, with 66 and 72% of the substrate remaining as free fatty acids, respectively. In contrast, both arachidonic and eicosapentaenoic acids were converted predominantly to PGFs and PGIs. The conversion was time dependent and complete by 30 min. The conversion patterns with eicosapentaenoic acid and arachidonic acid were essentially the same. The data suggest that goldfish cyclooxygenase can utilize two of the four potential substrates for prostaglandin synthesis. As fatty acid levels in fish vary with environmental temperature, substrate availability rather than cyclooxygenase preference may dictate the types of prostaglandins which are produced.

Effect of docosahexaenoic acid (DHA) on arachidonic acid metabolism and platelet function

Studies from our laboratory have suggested a role for ferrous iron in the metabolism of arachidonic acid and demonstrated that inhibitors of prostaglandin synthesis exert their effect by complexing with the heme group of cyclooxygenase. Docosahexaenoic acid (DHA) is a potent competitive inhibitor of arachidonic acid metabolism by sheep vesicular gland prostaglandin synthetase. In this study we have evaluated the effect of exogenously added DHA on platelet function and arachidonic acid metabolism. DHA at 150 microM concentration inhibited aggregation of platelets to 450 microM arachidonic acid. At this concentration DHA also inhibited the second wave of the platelet response to the action of agonists such as epinephrine, adenosine diphosphate and thrombin. Inhibition induced by this fatty acid could be overcome by the agonists at higher concentrations. DHA inhibited the conversion of labeled arachidonic acid to thromboxane by intact, washed platelet suspensions. However, platelets in plasma incubated first with DHA then washed and stirred with labeled arachidonate generated as much thromboxane as control platelets. These results suggest that the polyenoic acids, if released in sufficient quantities in the vicinity of cyclooxygenase, could effectively compete for the heme site and inhibit the conversion of arachidonic acid.

Ovarian and plasma PGE and PGF levels in naturally ovulating brook trout (Salvelinus fontinalis) and the effects of indomethacin on prostaglandin levels

Plasma and ovarian levels of PGE and PGF were measured by radioimmunoassay in naturally ovulating brook trout (Salvelinus fontinalis). At 12 hours post-ovulation, PGF levels in plasma and ovarian tissue were significantly elevated over levels in gravid controls. Plasma PGF levels were still elevated 5-7 days post-ovulation. Indomethacin treatment (10 micrograms/gm body weight) of ovulatory brook trout significantly decreased plasma and ovarian PGF levels by 12 hours post-ovulation. No significant differences were observed in plasma PGE levels, though gravid controls contained significantly elevated ovarian PGE levels as compared to ovulated fish.

Docosahexaenoic acid is a strong inhibitor of prostaglandin but not leukotriene biosynthesis

Docosahexaenoic acid (DCHA), a major polyunsaturated acid component of fish lipid, is not a substrate for prostaglandin synthetase from ram seminal vesicles but is a strong competitive inhibitor (Ki, 0.36 microM) of the conversion by this enzyme of arachidonate (Km, 5.9 microM) to prostaglandins. In contrast, DCHA exhibits little interference to the conversion of arachidonate to metabolites on the leukotriene pathway. DCHA is a very poor substrate for the leukotriene-synthesizing system from RBL-1 cells and no formation of the C22 analog of leukotriene B could be detected from it. The C22 analog of leukotriene C4 was produced by chemical synthesis from DCHA and found to be less than 1/10,000th as active as leukotriene C4 in contracting guinea pig ileum. The DCHA used in this work was obtained in greater than 99.8% purity by a practical process developed for its separation from fish lipid. The cardiovascular protective effects ascribed to dietary intake of fish lipid by certain populations may be due in part to the biological action of DCHA, including the inhibition of prostaglandin biosynthesis.

Synthesis of diene prostaglandins in freshwater fish

Biosynthesis of PGD2, PGE2 and PGF2 alpha in four species of freshwater fish, Tilapia mossambica, Cyprinus carpio, Heteropneustes fossilis and Clarius batrachus was studied. Both arachidonic acid and PGH2 were used as substrates. When PGH2 replaced arachidonic acid in the enzymic reaction, there was a 3- to 4-fold increase in PGE2 synthesis, but no such increase in the synthesis of PGF2 alpha and PGD2 was observed.

Determination of prostaglandins and thromboxane as their pentafluorobenzyl-trimethylsilyl derivatives by electron-capture gas chromatography

The optimization of the parameters affecting the chromatographic properties and separation of prostaglandin pentafluorobenzyl derivatives by gas chromatography using electron-capture detection is described. The effects of composition and flow-rate of carrier gas, temperatures of detector and column, and nature of stationary phases on the detector response to different pentafluorobenzyl (both oxime and ester) trimethylsilyl ether derivatives of prostaglandins were systemically examined. The stability of some selected prostaglandin derivatives at -20 degrees C was also determined. After standardizing these parameters, prostaglandins and related compounds from biological samples, e.g. semen, rat aorta, dog serum and trout gill were successfully analyzed. Identification of prostaglandins was confirmed by gas chromatography-mass spectrometry.

Extraction and purification of prostaglandins and thromboxane from biological samples for gas chromatographic analysis

An efficient extraction procedure for the isolation of prostaglandins (PGs) from biological samples for their subsequent quantification by gas chromatography-electron capture detection (GC-ECD) is described. PGs were extracted from lung, kidney, spleen and stomach fundus into ethyl acetate at different pHs. The highest recovery and least extraction of contaminating pigments was obtained at pH 4.5. Pigments and other contaminants are removed by thin layer chromatography using a solvent system chloroform-isopropyl alcohol-ethanol-formic acid (45:5:0.5:0.3). The isolated PGs were determined by GC-ECD after appropriate derivatization. The overall recovery of PGs using this procedure is 60%.