Hepoxilins and trioxilins in barnacles: an analysis of their potential roles in egg hatching and larval settlement

Biotransformation of Polyunsaturated Fatty Acids to Trioxilins by Lipoxygenase from Pleurotus sajor-caju

A lipoxygenase from Pleurotus sajor-caju (PsLOX) was cloned, expressed in Escherichia coli, and purified as a soluble protein with a specific activity of 629 μmol/min/mg for arachidonic acid (AA). The native PsLOX exhibited a molecular mass of 146 kDa, including a 73-kDa homodimer, as estimated by gel-filtration chromatography. The major products converted from polyunsaturated fatty acids (PUFAs), including AA, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), were identified as trioxilins (TrXs), namely 13,14,15-TrXB3 , 13,14,15-TrXB4 , and 15,16,17-TrXB5 , respectively, through high-performance liquid chromatography (HPLC) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) analyses. The enzyme displayed its maximum activity at pH 8.0 and 20 °C. Under these conditions, the specific activity and catalytic efficiency of PsLOX for PUFAs exhibited the following order: AA>EPA>DHA. Based on HPLC analysis and substrate specificity, PsLOX was identified as an arachidonate 15-LOX. PsLOX efficiently converted 10 mM of AA, EPA, and DHA to 8.7 mM of 13,14,15-TrXB3 (conversion rate: 87 %), 7.9 mM of 13,14,15-TrXB4 (79 %), and 7.2 mM of 15,16,17-TrXB5 (72 %) in 15, 20, and 20 min, respectively, marking the highest conversion rates reported to date. Collectively, our results demonstrate that PsLOX is an efficient TrXs-producing enzyme.

Lipoxygenases and Lipoxygenase Products in Marine Diatoms

Marine diatoms negatively affect reproduction and later larval development of dominant zooplankton grazers such as copepods, thereby lowering the recruitment of the next generations of these small crustaceans that are a major food source for larval fish species. The phenomenon has been explained in terms of chemical defense due to grazer-induced synthesis of oxylipins, lipoxygenase-derived oxygenated fatty acid derivatives. Since this first report, studies about diatom oxylipins have multiplied and broadened toward other aspects concerning bloom dynamics, cell growth, and cell differentiation. Diatom oxylipins embrace a number of diverse structures that are recognized as chemical signals in ecological and physiological processes in many other organisms. In diatoms, the most studied examples include polyunsaturated aldehydes (PUAs) and nonvolatile oxylipins (NVOs). The purpose of this chapter is to provide the analytical tools to deal with identification, analysis and biosynthesis of these compounds. Emphasis is given to identification of the enzymatic steps and characterization of the species-specific lipoxygenases even in absence of the availability of molecular information.

Biotransformation of polyunsaturated fatty acids to bioactive hepoxilins and trioxilins by microbial enzymes

Hepoxilins (HXs) and trioxilins (TrXs) are involved in physiological processes such as inflammation, insulin secretion and pain perception in human. They are metabolites of polyunsaturated fatty acids (PUFAs), including arachidonic acid, eicosapentaenoic acid and docosahexaenoic acid, formed by 12-lipoxygenase (LOX) and epoxide hydrolase (EH) expressed by mammalian cells. Here, we identify ten types of HXs and TrXs, produced by the prokaryote Myxococcus xanthus, of which six types are new, namely, HXB₅, HXD₃, HXE₃, TrXB₅, TrXD₃ and TrXE₃. We succeed in the biotransformation of PUFAs into eight types of HXs (>35% conversion) and TrXs (>10% conversion) by expressing M. xanthus 12-LOX or 11-LOX with or without EH in Escherichia coli. We determine 11-hydroxy-eicosatetraenoic acid, HXB₃, HXB₄, HXD₃, TrXB₃ and TrXD₃ as potential peroxisome proliferator-activated receptor-γ partial agonists. These findings may facilitate physiological studies and drug development based on lipid mediators.

Hepoxilins (HXs) and trioxilins (TrXs) are lipid metabolites with roles in inflammation and insulin secretion. Here, the authors discover a prokaryotic source of HXs and TrXs, identify the biosynthetic enzymes and heterologously express HXs and TrXs in E. coli.

Characterization of a New Trioxilin and a Sulfoquinovosyl Diacylglycerol with Anti-Inflammatory Properties from the Dinoflagellate Oxyrrhis marina

Two new compounds—a trioxilin and a sulfoquinovosyl diacylglycerol (SQDG)—were isolated from the methanolic extract of the heterotrophic dinoflagellate Oxyrrhis marina cultivated by feeding on dried yeasts. The trioxilin was identified as (4Z,8E,13Z,16Z,19Z) -7(S),10(S),11(S)-trihydroxydocosapentaenoic acid (1), and the SQDG was identified as (2S)-1-O-hexadecanosy-2-O-docosahexaenoyl-3-O-(6-sulfo-α-d-quinovopyranosyl)-glycerol (2) by a combination of nuclear magnetic resonance (NMR) spectra, mass analyses, and chemical reactions. The two compounds were associated with docosahexaenoic acid, which is a major component of O. marina. The two isolated compounds showed significant nitric oxide inhibitory activity on lipopolysaccharide-induced RAW264.7 cells. Compound 2 showed no cytotoxicity against hepatocarcinoma (HepG2), neuroblastoma (Neuro-2a), and colon cancer (HCT-116) cells, while weak cytotoxicity was observed for compound 1 against Neuro-2a cells.

An improved barnacle attachment inhibition assay

The Balanus amphitrite attachment inhibition assay, developed by Rittschof et al. (1992), has been widely used for screening antifouling compounds. One shortcoming of this assay, however, is the low (often < 40%) attachment rate of cyprids, including in the controls that contain seawater only. In this study, trapping of cyprids at the air-water interface was found to be a main contributor to the low attachment rate. Procedures to eliminate the air-water interface were thus introduced. With the improved bioassay, a much higher cyprid attachment rate (>70%) was attained. To further illustrate the usefulness of the improved assay (ie eliminating the air-water interface), the effects of the length of cyprid storage and the effect of a reference biocide, tributyltin chloride, on the survival and attachment rate of the cyprids were examined. The length of cyprid storage was important, with newly molted cyprids, 3- to 9-day old cyprids and 12-day old cyprids having an attachment rate of 43%,>75% and 36%, respectively. The low attachment rate in the newly molted cyprids was due to a high percentage of cyprids that still swam at the end of exposure period, whereas the low attachment rate in the 12-day old cyprids was due to a high mortality rate. The cyprids showed an EC50 of 22 microg l(-1) for attachment inhibition and LC50 of 25 microg l(-1) for mortality. It is concluded that the air-water interface has an important confounding effect on cyprid attachment rate in the conventional B. amphitrite attachment assay. By eliminating the air-water interface more robust quantitative assay results were obtained.

Biosynthesis and functions of eicosanoids generated by the coelomocytes of the starfish, Asterias rubens

Eicosanoids are a group of oxygenated fatty acid derivatives formed from C20 polyunsaturated fatty acids, including arachidonic and eicosapentaenoic acids. The potential of the coelomocytes of the starfish, Asterias rubens, to generate eicosanoids through the cyclooxygenase (COX) and lipoxygenase (LOX) pathways was investigated using reverse-phase high performance liquid chromatography, enzyme immunoassay and gas chromatography-mass spectrometry. The principal LOX product was identified as 8-hydroxyeicosatetraenoic acid (8-HETE) with 8-hydroxyeicosapentaenoic acid (8-HEPE) synthesised at significantly lower levels. No classical prostaglandins (PG), such as PGE2 or PGD2, were found to be generated by ionophore-challenged coelomocytes. Incubation of coelomocytes with lipopolysaccharides from either Escherichia coli or Salmonella abortus failed to induce an increase in generation of LOX products and the presence of 8-HETE (0-25 microM) had no significant effect on the in vitro phagocytic activity of Asterias coelomocytes. Neither indomethacin (a COX inhibitor) or esculetin (a LOX inhibitor) had any effect on the clearance of the bacterium, Vibrio splendidus, from the coelomic cavity of starfish suggesting that products of these enzymes are not involved in such coelomocyte responses to foreign particles.

Locating the barnacle settlement pheromone: spatial and ontogenetic expression of the settlement-inducing protein complex of Balanus amphitrite

Barnacles are prominent members of hard substratum benthic communities and their study has been important to advances in experimental ecology and contemporary ecological theory. Having recently characterized the cue to gregarious settlement of Balanus amphitrite, the settlement-inducing protein complex (SIPC), we use two polyclonal antibodies to examine the tissue distribution and ontogenetic expression of this glycoprotein. These antibodies were raised against two separate peptides located near the N- and C-termini of the SIPC and were used to detect the glycoprotein by western blotting and immunohistochemistry. By in situ hybridization we also show that the SIPC mRNA co-occurs with the expressed glycoprotein in the cuticles of both nauplius and cypris larval stages and the adult. In the larvae, the SIPC is expressed most strongly in the mouthparts and the hindgut of the stage 2 nauplius and in the thoracopods, antennules and bivalved carapace of the cyprid. In adult B. amphitrite, the expressed SIPC is present in protein extracts of the shell and in all organs that are lined by cuticular tissues. We suggest that the SIPC is produced by the epidermal cells that secrete the cuticle and discuss these observations with regard to earlier studies and the role of the SIPC as a contact pheromone.

Smelly feet are not always a bad thing: the relationship between cyprid footprint protein and the barnacle settlement pheromone

A critical phase in the life cycle of sessile benthic marine invertebrates is locating a suitable substratum for settlement. For barnacles, it is the lecithotrophic cypris larva that makes this plankto-benthic transition. In exploring possible substrata for settlement, the cyprid leaves behind 'footprints' of a proteinaceous secretion that reportedly functions as a temporary adhesive, and also acts as a secondary cue in larval-larval interactions at settlement. Here, we show that two polyclonal antibodies raised against peptides localized at the N- and C-terminal regions of the adult settlement cue--the settlement-inducing protein complex (SIPC)--could both detect 'temporary adhesive' indicating that the SIPC is either a component of this secretion or that they are the same protein.

The identification and role of a novel eicosanoid in the reproductive behaviour of barnacles (Balanus balanus)

Post-copulatory behaviour in barnacles involves a violent rocking movement of the opercular valves, which is thought to contribute to the expulsion of oocytes through the oviduct into the mantle cavity where they are fertilised. We demonstrate in this study that the seminal vesicles/testis of the subtidal barnacle Balanus balanus produce a biologically active factor,barnacle muscle stimulatory factor (BMSF), which causes a significant increase in cirral and body muscular activity. BMSF was identified using a combination of high performance liquid chromatography and mass spectrometry as a novel eicosanoid/oxylipin, 8,13-dihydroxyeicosapentaenoic acid. This is rapidly inactivated under mild acid conditions to form a complex range of triene and pentaene chromophore-containing products that have only been partially identified. Injection of purified BMSF into the mantle cavity of barnacles caused the rocking movements of the opercular valves as reported following fertilisation. In excised barnacles, it also caused muscular contractions of the whole body mass. The breakdown products of BMSF, however, were without such activities. The function of BMSF in facilitating fertilisation in barnacles is comparable to the role of other eicosanoids in human reproduction, reinforcing the view that these compounds have conserved activities in both invertebrates and vertebrates.

Marine chemical ecology

This review covers the recent marine chemical ecology literature for phytoplankton, macroalgae, sponges and other benthic invertebrates; 249 references are cited.

Epoxide hydrolases: their roles and interactions with lipid metabolism

The epoxide hydrolases (EHs) are enzymes present in all living organisms, which transform epoxide containing lipids by the addition of water. In plants and animals, many of these lipid substrates have potent biologically activities, such as host defenses, control of development, regulation of inflammation and blood pressure. Thus the EHs have important and diverse biological roles with profound effects on the physiological state of the host organisms. Currently, seven distinct epoxide hydrolase sub-types are recognized in higher organisms. These include the plant soluble EHs, the mammalian soluble epoxide hydrolase, the hepoxilin hydrolase, leukotriene A4 hydrolase, the microsomal epoxide hydrolase, and the insect juvenile hormone epoxide hydrolase. While our understanding of these enzymes has progressed at different rates, here we discuss the current state of knowledge for each of these enzymes, along with a distillation of our current understanding of their endogenous roles. By reviewing the entire enzyme class together, both commonalities and discrepancies in our understanding are highlighted and important directions for future research pertaining to these enzymes are indicated.

Evidence for different pharmacological targets for imidazoline compounds inhibiting settlement of the barnacleBalanus improvisus

We describe the effect of eight different imidazoline/guanidinium compounds on the settlement and metamorphosis of larvae of the barnacle Balanus improvisus. These agents were chosen on the basis of their similar pharmacological classification in vertebrates and their chemical similarity to medetomidine and clonidine, previously described as highly potent settlement inhibitors (nanomolar range). Seven of the tested compounds were found to inhibit settlement in a dose-dependent manner in concentrations ranging from 100 nM to 10 microM without any significant lethal effects. In vertebrate systems these substances have overlapping functions and interact with both alpha-adrenoceptors as well as imidazoline binding sites. Antagonizing experiments using the highly specific alpha(2)-antagonist methoxy-idazoxan or agmatine (the putative endogenous ligand at imidazoline receptors) were performed to discriminate between putative pharmacological mechanisms involved in the inhibition of cyprid settlement. Agmatine was not able to reverse the effect of any of the tested compounds. However, methoxy-idazoxan almost completely abolished the settlement inhibition mediated by guanabenz (alpha(2)-agonist, I(2) ligand), moxonidine (alpha(2)-agonist, I(1) ligand) and tetrahydrozoline (alpha-agonist, I(2) ligand). The actions of cirazoline (alpha(1)-agonist, I(2) ligand) BU 224 (I(2) ligand) and metrazoline (I(2) ligand) were not reversed by treatment with methoxy-idazoxan. These results suggest that the settlement inhibition evoked by the I(2) ligands and alpha(2)-agonists used in this study of the neurologically simple but well-organized barnacle larva is mediated through different physiological targets important in the overall settlement process.

Prostaglandins in non-insectan invertebrates: recent insights and unsolved problems

Prostaglandins (PG) are oxygenated derivatives of C20 polyunsaturated fatty acids including arachidonic and eicosapentaenoic acids. In mammals, these compounds have been shown to play key roles in haemostasis, sleep-wake regulation, smooth muscle tone, and vaso-, temperature and immune regulation. In invertebrates, PGs have been reported to perform similar roles and are involved in the control of oogenesis and spermatogenesis, ion transport and defence. Although there is often a detailed understanding of the actions of these compounds in invertebrates such as insects, knowledge of their mechanism of biosynthesis is often lacking. This account provides a critical review of our current knowledge on the structure and modes of biosynthesis of PGs in invertebrates, with particular reference to aquatic invertebrates. It emphasises some of the most recent findings, which suggest that some PGs have been misidentified.

Prostaglandins in invertebrates can be categorised into two main types; the classical forms, such as PGE2 and PGD2 that are found in mammals, and novel forms including clavulones, bromo- and iodo-vulones and various PGA2 and PGE2 esters. A significant number of reports of PG identification in invertebrates have relied upon methods such as enzyme immunoassay that do not have the necessary specificity to ensure the validity of the identification. For example, in the barnacle Balanus amphitrite, although there are PG-like compounds that bind to antibodies raised against PGE2, mass spectrometric analysis failed to confirm the presence of this and other classical PGs. Therefore, care should be taken in drawing conclusions about what PGs are formed in invertebrates without employing appropriate analytical methods. Finally, the recent publication of the Ciona genome should facilitate studies on the nature and mode of biosynthesis of PGs in this advanced deuterostomate invertebrate.

Eicosanoid generation in the intertidal barnacle,Balanus perforatus—effect of season and reproductive status

The nature and quantity of the principal lipoxygenase (LO) products generated by the intertidal barnacle Balanus perforatus were examined at monthly intervals and their potential involvement in reproductive events was investigated. The main mono-hydroxy products generated were found to be formed through the action of an 8-lipoxygenase (8-LO) activity and were the mono-hydroxy fatty acids, 8-hydroxyeicosapentaenoic acid (HEPE) and 8-hydroxyeicosatetraenoic acid. Generation of these products was found to be correlated with the environmental seawater temperature, although no change in either 8-LO activity or the precursor fatty acid levels in total phospholipids was found with the time of the year. Changes in fatty acid composition measured in animals collected from summer and winter conditions were found to follow the pattern expected by homeoviscous adaptation of a cold-acclimated animal. Oogenesis was found to occur in August and was linked to a significant reduction in 8-HEPE generation. Spermatozoa were found to be present year-round in the seminal vesicles although the testes became atrophic during the winter months.