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

Feeding ecology of redfish (Sebastes sp.) inferred from the integrated use of fatty acid profiles as complementary dietary tracers to stomach content analysis

In the northern Gulf of St. Lawrence (nGSL), redfish (Sebastes mentella and Sebastes fasciatus combined) are at record levels of abundance following the strong recruitment of three consecutive cohorts in 2011-2013 and have become by far the most abundant demersal fish in the region. Understanding redfish trophic relationships is essential for the effective management and conservation of species in the nGSL ecosystem. To date, description and quantification of redfish diet in the region have been restricted to conventional stomach content analysis (SCA). Using analysis of fatty acid (FA) profiles as complementary dietary tracers, the authors conducted multivariate analyses on 350 livers of redfish which were collected in combination with stomach contents during a bottom-trawl scientific survey in August 2017. The predator FA profiles were compared to those of eight different redfish prey types identified as dietary important with SCA. Results suggested similitude between SCA and FA results, with zooplankton prey being more related to small (<20 cm) and medium (20-30 cm) redfish (16:1n7, 20:1n?, 22:1n9 and 20:5n3) than large (≥30 cm) ones, whereas shrimp prey seemed more related to large redfish size classes (18:2n6 and 22:6n3) relative to the small and medium ones. Although the SCA offers a glimpse in the diet only based on the most recently consumed prey, analysis of FA profiles provides a mid-term view indicating pelagic zooplankton consumption on calanoid copepod and confirming high predation pressure on shrimp. This study constitutes the first attempt of combining FA with SCA to assess the diet of redfish, highlights the benefits of FA as a qualitative tool and suggests improvements for future studies.

Role and relevance of fish cell lines in advanced in vitro research

Introduction

Cell line derived from fish has been established as a promising tool for studying many key issues of aquaculture covering fish growth, disease, reproduction, genetics, and biotechnology. In addition, fish cell lines are very useful in vitro models for toxicological, pathological, and immunological studies. The easier maintenance of fish cell lines in flexible temperature regimes and hypoxic conditions make them preferable in vitro tools over mammalian cell lines. Great excitement has been observed in establishing and characterizing new fish cell lines representing diverse fish species and tissue types. The well-characterized and authenticated cell lines are of utmost essential as these represent cellular functions very similar to in vivo state of an organism otherwise it would affect the reproducibility of scientific research.

Conclusion

The fish cell lines have exhibited encouraging results in several key aspects of in vitro research in aquaculture including virology, nutrition and metabolism, production of vaccines, and transgenic fish production. The review paper reports the cell lines developed from fish, their characterization, and biobanking along with their potential applications and challenges in in vitro research.

Dietary ARA Improves COX Activity in Broodstock and Offspring Survival Fitness of a Model Organism (Medaka Oryzias latipes)

A 3-week feeding trial was conducted in medaka broodstock (age five months) to examine the effect of dietary arachidonic acid (ARA) level (range: 4-23 mg g^-1 of total fatty acids (TFAs)) on fertility, cyclooxygenase (COX) activity, egg size, sperm motility parameters, hatching rate and weight of hatch, survival and growth of larvae. After spawn induction and dietary exposure to 4 mg ARA g^-1 TFA, broodstock were fed a diet containing ARA in the amounts: 4 (continued, as control), 5, 14 and 23 mg g^-1 TFA. COX1 activity in the liver and the number of COX2-positive cells in the ovaries was increased in females fed the diets containing the two highest amounts of ARA. The highest sperm motility parameters were observed in males fed a diet containing 23 mg ARA g^-1 TFA. The hatchability rate and bodyweight of hatchlings were higher in the group obtained from broodstock fed a diet containing 23 mg ARA g^-1 TFA (79% and 0.66 mg fish^-1, respectively) compared with 4 mg ARA g^-1 TFA (50% and 0.40 mg fish^-1). The average mortality of offspring obtained from this group at 7 days post hatching was significantly higher than that of all other groups.

Embryo and larva development in Dentex dentex, a marine pelagophil teleost: an endeavor to find a series of new fatty acid interrelations

Although the fatty acid (FA) requirements of marine teleosts not only are a function of the amount of each FA individually, but also of the relative proportions of the FAs; mostly, the interactions have been ignored and merely limited to a few interrelations of 20:4[n-6], 20:5[n-3], and 22:6[n-3]. To address this shortcoming, viable eggs of Dentex dentex were obtained from broodfish in captivity. Nine viability parameters (VP) (i.e., floating rate (FR), hatching rate (HR), and survival rate (SR) from day 0 to 5 posthatch (dph)) that are currently used in mariculture systems were determined. Egg FAs were characterized and quantified. One hundred and twenty ratios were made based on the FA contents estimated. Sixty-four ratios were significantly and strongly correlated to embryo/larva success through 201 simple regression models (r(2) = 0.640-0.948; P = 0.006-P < 0.001). Of the 201 significant relationships found, -12, -5, -2, -3, -22, -23, ∼21, and -13% show the relations of the egg FA ratios with FR, HR, and SR at 0, 1, 2, 3, 4, and 5 dph, respectively. All the FAs characterized in this study were significantly correlated to VPs through either their individual relative proportions or relative proportion of their combinations. This study, for the first time, presents a series of new FA interrelations and uncovers their biological meanings under both basic and applied aspects through correlating them to embryo/larva success.

Investigation of highly unsaturated fatty acid metabolism in the Asian sea bass, Lates calcarifer

Lates calcarifer, commonly known as the Asian sea bass or barramundi, is an interesting species that has great aquaculture potential in Asia including Malaysia and also Australia. We have investigated essential fatty acid metabolism in this species, focusing on the endogenous highly unsaturated fatty acid (HUFA) synthesis pathway using both biochemical and molecular biological approaches. Fatty acyl desaturase (Fad) and elongase (Elovl) cDNAs were cloned and functional characterization identified them as ∆6 Fad and Elovl5 elongase enzymes, respectively. The ∆6 Fad was equally active toward 18:3n-3 and 18:2n-6, and Elovl5 exhibited elongation activity for C18-20 and C20-22 elongation and a trace of C22-24 activity. The tissue profile of gene expression for ∆6 fad and elovl5 genes, showed brain to have the highest expression of both genes compared to all other tissues. The results of tissue fatty acid analysis showed that the brain contained more docosahexaenoic acid (DHA, 22:6n-3) than flesh, liver and intestine. The HUFA synthesis activity in isolated hepatocytes and enterocytes using [1-(14)C]18:3n-3 as substrate was very low with the only desaturated product detected being 18:4n-3. These findings indicate that L. calcarifer display an essential fatty acid pattern similar to other marine fish in that they appear unable to synthesize HUFA from C18 substrates. High expression of ∆6 fad and elovl5 genes in brain may indicate a role for these enzymes in maintaining high DHA levels in neural tissues through conversion of 20:5n-3.

Divergent cyclooxygenase responses to fatty acid structure and peroxide level in fish and mammalian prostaglandin H synthases

Prostanoid synthesis in mammalian tissues is regulated at the level of prostaglandin H synthase (PGHS) cyclooxygenase catalysis by the availability and structure of substrate fatty acid and the availability of peroxide activator. Two major PGHS isoforms, with distinct pathophysiological functions and catalytic regulation, have been characterized in mammals; a functionally homologous PGHS isoform pair has been cloned from an evolutionarily distant vertebrate, brook trout. The cyclooxygenase activities of recombinant brook trout PGHS-1 and -2 were characterized to test the generality of mammalian regulatory paradigms for substrate specificity, peroxide activation, and product shifting by aspirin. Both trout cyclooxygenases had much more restrictive substrate specificities than their mammalian counterparts, with pronounced discrimination toward arachidonate (20:4n-6) and against eicosapentaenoate (20:5n-3) and docosahexaenoate (22:6n-3), the latter two prominent in trout tissue lipids. Aspirin treatment did not increase lipoxygenase-type catalysis by either trout enzyme. Both trout enzymes had higher requirements for peroxide activator than their mammalian counterparts, though the preferential peroxide activation of PGHS-2 over PGHS-1 seen in mammals was conserved in the fish enzymes. The divergence in cyclooxygenase characteristics between the trout and mammalian PGHS proteins may reflect accomodations to differences among vertebrates in tissue lipid composition and general redox state.

Selective polyunsaturated fatty acids enrichment in phospholipids from neuronal-derived cell lines

Most studies aimed at exploring the molecular and cellular properties of plasma membranes in neural tissues make use of cell lines. However, cell membrane lipid composition of cell lines is notably different from that of brain tissues where they presumably derive from. Using septal-derived SN56 cells and hippocampal-derived HT22 cells, we demonstrated that cell lines exhibit lower contents of saturated (18:0) and long polyunsaturated fatty acids (PUFA; 20:4n-6 and especially 22:6n-3), as well as higher monounsaturated fatty acid contents (mainly 18:1n-9), compared to mouse brain. Also, cell lines exhibited higher contents of sterol esters and lower contents of cholesterol and phospholipids, especially phosphatidylethanolamine and phosphatidylserine. We have also evaluated the effects of different (n-3/n-6) PUFA enrichments on fatty acid and phospholipid contents in these cell lines. Our results show that enrichment of culture medium with 22:6n-3 and 20:4n-6 in a 70/30 proportion during 48 h, using fat-free bovine serum albumin as vehicle, successfully readjusted fatty acid profiles in cell line-polar lipids to values found in natural nerve cells. Interestingly, no differences in cell survival were observed upon enrichment. The generalization of these methodologies would allow a more feasible adaptation of cellular models to the study of in vivo nerve physiology.

Arachidonic acid in astrocytes blocks Ca(2+) oscillations by inhibiting store-operated Ca(2+) entry, and causes delayed Ca(2+) influx

ATP-elicited oscillations of the concentration of free intracellular Ca(2+) ([Ca(2+)](i)) in rat brain astrocytes were abolished by simultaneous arachidonic acid (AA) addition, whereas the tetraenoic analogue 5,8,11,14-eicosatetraynoic acid (ETYA) was ineffective. Inhibition of oscillations is due to suppression by AA of intracellular Ca(2+) store refilling. Short-term application of AA, but not ETYA, blocked Ca(2+) influx, which was evoked by depletion of stores with cyclopiazonic acid (CPA) or thapsigargin (Tg). Addition of AA after ATP blocked ongoing [Ca(2+)](i) oscillations. Prolonged AA application without or with agonist could evoke a delayed [Ca(2+)](i) increase. This AA-induced [Ca(2+)](i) rise developed slowly, reached a plateau after 5 min, could be reversed by addition of bovine serum albumin (BSA), that scavenges AA, and was blocked by 1 microM Gd(3+), indicative for the influx of extracellular Ca(2+). Specificity for AA as active agent was demonstrated by ineffectiveness of C16:0, C18:0, C20:0, C18:2, and ETYA. Moreover, the action of AA was not affected by inhibitors of oxidative metabolism of AA (ibuprofen, MK886, SKF525A). Thus, AA exerted a dual effect on astrocytic [Ca(2+)](i), firstly, a rapid reduction of capacitative Ca(2+) entry thereby suppressing [Ca(2+)](i) oscillations, and secondly inducing a delayed activation of Ca(2+) entry, also sensitive to low Gd(3+) concentration.

Platelet-activating factor increases prostaglandin E(2) release from astrocyte-enriched cortical cell cultures

The phospholipid mediator platelet-activating factor (PAF) increased the release of prostaglandin E(2) (PGE(2)) from astrocyte-enriched cortical cell cultures in a concentration- and time-dependent manner. The nonhydrolyzable PAF analog methylcarbamyl-PAF (mc-PAF), the PAF intermediate lyso-PAF, and arachidonic acid (AA) also produced this effect. In contrast, phosphatidlycholine (PC) and lyso-PC, lipids that are structurally similar to PAF and lyso-PAF, had no effect on PGE(2) production, suggesting that PAF-induced PGE(2) release is not the consequence of nonspecific phospholipid-induced membrane perturbation. Antagonism of intracellular PAF binding sites completely abolished the ability of mc-PAF and lyso-PAF to mobilize PGE(2,) and attenuated the AA effect. Antagonism of the G-protein-coupled PAF receptor in plasma membranes had no significant effect on mc-PAF, lyso-PAF or AA-induced PGE(2) release. Based on the present findings, we hypothesize that intracellular PAF is a physiologic stimulus of PGE(2) production in astrocytes.

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.