Eicosanoid biosynthesis in an advanced deuterostomate invertebrate, the sea squirt (Ciona intestinalis)

New maresin conjugates in tissue regeneration pathway counters leukotriene D4-stimulated vascular responses

Resolution of acute inflammation is governed, in part, by lipid mediator class switching from proinflammatory eicosanoids to specialized proresolving mediators, including a recently identified new pathway of mediators, termed maresin conjugates in tissue regeneration (MCTR), which includes MCTR1, MCTR2, and MCTR3. Here, we addressed whether each MCTR can impact the known vascular actions of cysteinyl leukotrienes. Leukotriene D₄ (LTD₄; 1.5 nmol/mouse) initiated vascular leakage in mouse cremaster vessels, which was reduced (>75%) by MCTR1 and MCTR2 (0.15 nmol each). With isolated Ciona intestinalis (sea squirt) primordial hearts, LTD₄ (1-100 nM) induced negative inotropic action and lowered heartbeats 20-30%. Each MCTR (1-100 nM) prevented LTD₄-reduced heart rates. With human cysteinyl leukotriene receptor-1 (CysLT1) expressed in CHO cells, each MCTR (10-100 nM) significantly reduced LTD₄-initiated signaling. To assess the contribution of CysLT1 in the proresolving actions of MCTR, we carried out human macrophage (MΦ) phagocytosis. Each MCTR (0.1-10 nM) stimulated human MΦ phagocytosis of live Escherichia coli, whereas LTD₄ did not stimulate phagocytosis. MCTR-activated phagocytosis was significantly blocked by a pharmacologic receptor antagonist (MK571). With both CHO-CysLT1 and human MΦs, each MCTR competed for specific [³H]-LTD₄ binding with apparent lower affinity than LTD₄. Thus, each MCTR functionally interacts with human CysLT1 to pharmacologically counter-regulate vascular responses and stimulate physiologic phagocytosis with MΦs.-Chiang, N., Riley, I. R., Dalli, J., Rodriguez, A. R., Spur, B. W., Serhan, C. N. New maresin conjugates in tissue regeneration pathway counters leukotriene D₄-stimulated vascular responses.

Lipid Mediator Metabolomics Via LC-MS/MS Profiling and Analysis

Solid-phase extraction coupled with liquid chromatography tandem mass spectrometry provides a robust and sensitive approach for the identification and quantitation of specialized pro-resolving mediators (lipoxins, resolvins, protectins, and maresins), their pathway markers and the classic eicosanoids. Here, we provide a detailed description of the methodologies employed for the extraction of these mediators from biological systems, setup of the instrumentation, sample processing, and then the procedures followed for their identification and quantitation.

Does promoting resolution instead of inhibiting inflammation represent the new paradigm in treating infections?

Infections arise when the host response is overwhelmed by pathogens leading to organ dysfunction. In some instances patients progress to more severe conditions, including septic shock, that are associated with increased mortality. Current strategies in treating infections aim at either blocking inflammation using inhibitors to pro-inflammatory molecules and/or inhibiting bacterial growth using antibiotics. These approaches find their origins in studies conducted by Joseph Lister who demonstrated that applying carbolic acid to wounds promoted wound healing without suppuration, reducing both the necessity of amputation and mortality. While this approach is still applicable to certain infections, inhibition of the immune response is also associated with increased mortality, especially in septic patients. In many instances sepsis survivors succumb later to persistent, recurrent, nosocomial and secondary infections. This, together with a rise in resistance to many frontline antibiotics, has prompted a search for alternative ways to treat infections. Recent studies investigating processes engaged by the host response during self-resolving infections identified a novel group of mediators, termed as specialized pro-resolving mediators (SPM). These molecules, produced via the enzymatic conversion of essential fatty acids, actively reprogram the immune response to promote clearance of invading pathogens, and counter-regulate the production of inflammation-initiating molecules. Furthermore, recent studies also demonstrate that these mediators promote tissue repair and regeneration, essential processes in the re-establishment of barrier and prevention of re-infection. The scope of the present review is to discuss the evidence underpinning the endogenous protective roles of these novel mediators, as well as the evidence demonstrating that dysregulation in their production and actions contribute to disease pathogenesis in infections. This review will also discuss the potential of resolution pharmacology-based approaches in developing new therapeutics for combatting infections that do not interfere with the immune response.

Human pharmaceuticals in the marine environment: Focus on exposure and biological effects in animal species

Marine waters have been poorly investigated for the occurrence of pharmaceutical contamination. Recent data confirm that pharmaceuticals occur widely in marine and coastal environments; therefore, assessment of potential risk to marine species needs further efforts. The present study represents the first extensive review of pharmaceutical contamination in marine environments addressing the effects on the marine biota analyzed at the molecular, cellular, and individual levels. Because pharmaceuticals differ from conventional pollutants, being designed to interact with specific physiological pathways at low doses, the most recent evidence on modes of action and physiological alterations on marine animal species are discussed. Data on spatial distributions of pharmaceuticals in waters and sediments, as well as bioaccumulation rates, are also presented. The present review also seeks to expand knowledge of how the quality of coastal and marine environments could be efficiently monitored to anticipate possible health and environmental risks.

Ancestral genetic complexity of arachidonic acid metabolism in Metazoa

Eicosanoids play an important role in inducing complex and crucial physiological processes in animals. Eicosanoid biosynthesis in animals is widely reported; however, eicosanoid production in invertebrate tissue is remarkably different to vertebrates and in certain respects remains elusive. We, for the first time, compared the orthologs involved in arachidonic acid (AA) metabolism in 14 species of invertebrates and 3 species of vertebrates. Based on parsimony, a complex AA-metabolic system may have existed in the common ancestor of the Metazoa, and then expanded and diversified through invertebrate lineages. A primary vertebrate-like AA-metabolic system via cyclooxygenase (COX), lipoxygenase (LOX), and cytochrome P450 (CYP) pathways was further identified in the basal chordate, amphioxus. The expression profiling of AA-metabolic enzymes and lipidomic analysis of eicosanoid production in the tissues of amphioxus supported our supposition. Thus, we proposed that the ancestral complexity of AA-metabolic network diversified with the different lineages of invertebrates, adapting with the diversity of body plans and ecological opportunity, and arriving at the vertebrate-like pattern in the basal chordate, amphioxus.

Mucosal immunity in the gut: the non-vertebrate perspective

Much is now known about the vertebrate mechanisms involved in mucosal immunity, and the requirement of commensal microbiota at mucosal surfaces for the proper functioning of the immune system. In comparison, very little is known about the mechanisms of immunity at the barrier epithelia of non-vertebrate organisms. The purpose of this review is to summarize key experimental evidence illustrating how non-vertebrate immune mechanisms at barrier epithelia compare to those of higher vertebrates, using the gut as a model organ. Not only effector mechanisms of gut immunity are similar between vertebrates and non-vertebrates, but it also seems that the proper functioning of non-vertebrate gut defense mechanisms requires the presence of a resident microbiota. As more information becomes available, it will be possible to obtain a more accurate picture of how mucosal immunity has evolved, and how it adapts to the organisms' life styles.

Gene transcription and biomarker responses in the clam Ruditapes philippinarum after exposure to ibuprofen

Pharmaceuticals are a class of emerging environmental contaminants that continuously enter aquatic environments. Presently, little information is available about the effects of these substances on non-target organisms, such as bivalves. We investigated the effects of ibuprofen (IBU) on the clam Ruditapes philippinarum. Clams were exposed for 1, 3, 5 and 7 days to 0, 100 and 1000 μgIBU/L, and established biomarker responses (haemolymph lysozyme, gill acetylcholinesterase and digestive gland superoxide dismutase activities) as well as digestive gland transcriptome were evaluated. A two-way ANOVA revealed significant effects of both "IBU concentration" and "exposure duration" on biomarker responses. Overall, the enzyme activities were generally lower in IBU-exposed clams than in controls. Although limited knowledge of the mollusc transcriptome makes it difficult to interpret the effects of IBU on clams, the gene transcription analysis using DNA microarrays enabled the identification of the putative molecular mode of action of the IBU. The functional analysis of differentially transcribed genes suggests that IBU can interfere with various signalling pathways in clams, such as arachidonic acid metabolism, apoptosis, peroxisomal proliferator-activated receptors, and nuclear factor-kappa B. In addition, several genes involved in the metabolism of xenobiotics (e.g., glutathione S-transferase, sulfotransferase, cytochrome P450) were also found to be significantly affected by IBU exposure. In summary, the integrated approach of gene transcription analysis and biomarker responses facilitated the elucidation of the putative mechanisms of action of IBU in non-target species.

Effects of indomethacin and propranolol on Chironomus riparius and Physella (Costatella) acuta

New analytical methods are available for detecting novel xenobiotic compounds in freshwater systems. Pharmaceuticals are suspected of having effects on freshwater biota at very low concentrations, although the nature of these effects remains unclear. Previous data from the Llobregat River revealed a positive statistical relationship between the biomass of benthic macroinvertebrates and the presence of certain non-steroidal anti-inflammatory drugs (NSAIDs) and beta-blockers. Here, experiments were conducted with the midge Chironomus riparius and the freshwater snail Physella (Costatella) acuta in sediments and water, respectively. The sediments and water were treated with the pharmaceuticals propranolol and indomethacin, with the aims of assaying the effects of these compounds on the organisms and testing the statistical relationships observed in field. The variables measured were survival; C. riparius biomass; and the carbon/nitrogen ratio, lipid content and fertility of freshwater snails. Indomethacin in treated sediments induced an increase in C. riparius biomass, whereas propranolol inhibited growth, albeit at marginal statistical significance. By contrast, indomethacin in water had no effect on any of the parameters measured in P. acuta.

Outlining eicosanoid biosynthesis in the crustacean Daphnia

BACKGROUND

Eicosanoids are biologically active, oxygenated metabolites of three C20 polyunsaturated fatty acids. They act as signalling molecules within the autocrine or paracrine system in both vertebrates and invertebrates mainly functioning as important mediators in reproduction, the immune system and ion transport. The biosynthesis of eicosanoids has been intensively studied in mammals and it is known that they are synthesised from the fatty acid, arachidonic acid, through either the cyclooxygenase (COX) pathway; the lipoxygenase (LOX) pathway; or the cytochrome P450 epoxygenase pathway. However, little is still known about the synthesis and structure of the pathway in invertebrates.

RESULTS

Here, we show transcriptomic evidence from Daphnia magna (Crustacea: Branchiopoda) together with a bioinformatic analysis of the D. pulex genome providing insight on the role of eicosanoids in these crustaceans as well as outlining a putative pathway of eicosanoid biosynthesis. Daphnia appear only to have one copy of the gene encoding the key enzyme COX, and phylogenetic analysis reveals that the predicted protein sequence of Daphnia COX clusters with other invertebrates. There is no current evidence of an epoxygenase pathway in Daphnia; however, LOX products are most certainly synthesised in daphnids.

CONCLUSION

We have outlined the structure of eicosanoid biosynthesis in Daphnia, a key genus in freshwater ecosystems. Improved knowledge of the function and synthesis of eicosanoids in Daphnia and other invertebrates could have important implications for several areas within ecology. This provisional overview of daphnid eicosanoid biosynthesis provides a guide on where to focus future research activities in this area.

A shifted repertoire of endocannabinoid genes in the zebrafish (Danio rerio)

The zebrafish has served as a model organism for developmental biology. Sequencing its genome has expanded zebrafish research into physiology and drug-development testing. Several cannabinoid pharmaceuticals are in development, but expression of endocannabinoid receptors and enzymes remains unknown in this species. We conducted a bioinformatics analysis of the zebrafish genome using 17 human endocannabinoid genes as a reference set. Putative zebrafish orthologs were identified in filtered BLAST searches as reciprocal best hits. Orthology was confirmed by three in silico methods: phylogenetic testing, synteny analysis, and functional mapping. Zebrafish expressed orthologs of cannabinoid receptor 1, transient receptor potential channel vanilloid receptor 4, GPR55 receptor, fatty acid amide hydrolase 1, monoacylglycerol lipase, NAPE-selective phospholipase D, abhydrolase domain-containing protein 4, and diacylglycerol lipase alpha and beta; and paired paralogs of cannabinoid receptor 2, fatty acid amide hydrolase 2, peroxisome proliferator-activated receptor alpha, prostaglandin-endoperoxide synthase 2, and transient receptor potential cation channel subtype A1. Functional mapping suggested the orthologs of transient receptor potential vanilloid receptor 1 and peroxisome proliferator-activated receptor gamma lack specific amino acids critical for cannabinoid ligand binding. No orthologs of N-acylethanolamine acid amidase or protein tyrosine phosphatase, non-receptor type 22 were identified. In conclusion, the zebrafish genome expresses a shifted repertoire of endocannabinoid genes. In vitro analyses are warranted before using zebrafish for cannabinoid development testing.

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.

Evolutionary origins of the endocannabinoid system

Endocannabinoid system evolution was estimated by searching for functional orthologs in the genomes of twelve phylogenetically diverse organisms: Homo sapiens, Mus musculus, Takifugu rubripes, Ciona intestinalis, Caenorhabditis elegans, Drosophila melanogaster, Saccharomyces cerevisiae, Arabidopsis thaliana, Plasmodium falciparum, Tetrahymena thermophila, Archaeoglobus fulgidus, and Mycobacterium tuberculosis. Sequences similar to human endocannabinoid exon sequences were derived from filtered BLAST searches, and subjected to phylogenetic testing with ClustalX and tree building programs. Monophyletic clades that agreed with broader phylogenetic evidence (i.e., gene trees displaying topographical congruence with species trees) were considered orthologs. The capacity of orthologs to function as endocannabinoid proteins was predicted with pattern profilers (Pfam, Prosite, TMHMM, and pSORT), and by examining queried sequences for amino acid motifs known to serve critical roles in endocannabinoid protein function (obtained from a database of site-directed mutagenesis studies). This novel transfer of functional information onto gene trees enabled us to better predict the functional origins of the endocannabinoid system. Within this limited number of twelve organisms, the endocannabinoid genes exhibited heterogeneous evolutionary trajectories, with functional orthologs limited to mammals (TRPV1 and GPR55), or vertebrates (CB2 and DAGLbeta), or chordates (MAGL and COX2), or animals (DAGLalpha and CB1-like receptors), or opisthokonta (animals and fungi, NAPE-PLD), or eukaryotes (FAAH). Our methods identified fewer orthologs than did automated annotation systems, such as HomoloGene. Phylogenetic profiles, nonorthologous gene displacement, functional convergence, and coevolution are discussed.

Resveratrol: Preventing properties against vascular alterations and ageing

Cardiovascular diseases are the leading cause of death in developed countries where the common pathological substrate underlying this process is atherosclerosis. Several new concepts have emerged in relation to mechanisms that contribute to the regulation of the vascular diseases and associated inflammatory effects. Recently, potential antioxidants (vitamin E, polyphenols) have received much attention as potential anti-atherosclerotic agents. Among the polyphenols with health benefic properties, resveratrol, a phytoalexin of grape, seem to be a good candidate protecting the vascular walls from oxidation, inflammation, platelet aggregation, and thrombus formation. In this review, we focus on the mechanism of resveratrol cardiovascular benefic effects. We analyze, in relation with the different steps of atherosclerotic process, the resveratrol properties at multiple levels, such as cellular signaling, enzymatic pathways, apoptosis, and gene expression. We show and discuss the relationship with reactive oxygen species, regulation of pro-inflammatory genes including cycloxygenases and cytokines in molecular inflammatory and aging processes, and how the regulation of these activites by resveratrol can lead to a prevention of vascular diseases.

Occurrence and possible biological role of the endocannabinoid system in the sea squirt Ciona intestinalis

A cannabinoid receptor orthologue (CiCBR) has been described in the sea squirt Ciona intestinalis. Here we report that CiCBR mRNA expression is highest in cerebral ganglion, branchial pharynx, heart and testis of C. intestinalis, and that this organism also contains cannabinoid receptor ligands and some of the enzymes for ligand biosynthesis and inactivation. Using liquid chromatography-mass spectrometry, the endocannabinoid anandamide was found in all tissues analysed (0.063-5.423 pmol/mg of lipid extract), with the highest concentrations being found in brain and heart. The endocannabinoid 2-arachidonoylglycerol (2-AG) was fivefold more abundant than anandamide, and was most abundant in stomach and intestine and least abundant in heart and ovaries (2.677-50.607 pmol/mg of lipid extract). Using phylogenomic analysis, we identified orthologues of several endocannabinoid synthesizing and degrading enzymes. In particular, we identified and partly sequenced a fatty acid amide hydrolase (FAAH) orthologue, showing 44% identity with human FAAH and containing nearly all the amino acids necessary for a functional FAAH enzyme. Ciona intestinalis also contained specific binding sites for cannabinoid receptor ligands, and an amidase enzyme with pH-dependency and subcellular/tissue distribution similar to mammalian FAAHs. Finally, a typical C. intestinalis behavioural response, siphon reopening after closure induced by mechanical stimulation, was inhibited by the cannabinoid receptor agonist HU-210, and this effect was significantly attenuated by mammalian cannabinoid receptor antagonists.

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.

On the Evolutionary Origin of Cyclooxygenase (COX) Isozymes

In vertebrates, COX-1 and COX-2, two cyclooxygenase isozymes with different physiological functions and gene regulation, catalyze identical reactions in prostaglandin synthesis. It is still not understood why there are multiple forms of COX enzyme in the same cell type and when the evolutionary duplication of the COX gene occurred. Here we report the structure of two genes encoding for COX isozymes in the coral Gersemia fruticosa, the first non-vertebrate organism from which a cyclooxygenase was characterized. Both genes are about 20 kb in size and consist of nine exons. Intron/exon boundaries are well conserved between coral and mammalian COX genes. mRNAs of the previously reported G. fruticosa COX-A (GenBank trade mark accession number AY004222) and the novel COX-B share 94% sequence identity in the coding regions and less than 30% in the 5'- and 3'-untranslated region. Transcripts of both COX genes are detectable in coral cells, although the transcriptional level of COX-A is 2 orders of magnitude higher than COX-B. Expression of both coral genes in mammalian cells gave functional proteins with similar catalytic properties. By data base analyses we also detected and constructed different pairs of COX genes from the primitive chordates, Ciona savignyi and Ciona intestinalis. These two gene pairs encode proteins with 50% intra-species and only 70% cross-species sequence identity. Our results suggest that invertebrate COX gene pairs do not correspond to vertebrate COX-1 and COX-2 and are consistent with duplication of the COX gene having occurred independently in corals, ascidians, and vertebrates. It is evident that due to the importance and complexity of its regulatory role, COX has multiple isoforms in all organisms known to express it, and the genes encoding for the isozymes may to be regulated differently.

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

The barnacle life cycle has two key stages at which eicosanoids are believed to be involved in cellular communication pathways, namely the hatching of nauplii and the settlement of cypris larvae. Barnacle egg-hatching activity has previously been reported to reside in a variety of eicosanoids, including 8-hydroxyeicosapentaenoic acid and a number of tri-hydroxylated polyunsaturated fatty acid derivatives, the trioxilins. The production of the eicosapentaenoic acid metabolite trioxilin A4 (8,11,12-trihydroxy-5,9,14,17-eicosatetraenoic acid) by the barnacles Balanus amphitrite and Elminius modestus was confirmed using a combination of high-performance liquid chromatography and gas chromatography, both linked to mass spectrometry. In addition, both species also generated trioxilin A3 (8,11,12-trihydroxy-5,9,14-eicosatrienoic acid; an arachidonic acid-derived product), 8,11,12-trihydroxy-9,14,17-eicosatrienoic acid (a omega3 analogue of trioxilin A3; derived from omega3 arachidonic acid) and 10,13,14-trihydroxy-4,7,11,16,19-docosapentaenoic acid (a docosahexaenoic acid-derived product). In contrast to earlier reports, trioxilin A3 had no E. modestus egg-hatching activity at any of the concentrations tested (10(-9)-10(-6) mol l(-1)). The unstable epoxide precursor hepoxilin A3, however, caused significant levels of hatching at 10(-6) mol l(-1). Furthermore, the stable hepoxilin B3 analogue PBT-3 stimulated hatching at 10(-7) mol l(-1). Neither trioxilin A3, hepoxilin A3 or PBT-3 at 0.25-30 micromol l(-1) served as settlement cues for B. amphitrite cypris larvae.

Pulsed electromagnetic fields affect phenotype and connexin 43 protein expression in MLO-Y4 osteocyte-like cells and ROS 17/2.8 osteoblast-like cells

Osteocytes, the predominant cells in bone, are postulated to be responsible for sensing mechanical and electrical stimuli, transducing signals via gap junctions. Osteocytes respond to induced shear by increasing connexin 43 (Cx43) levels, suggesting that they might be sensitive to physical stimuli like low-frequency electromagnetic fields (EMF). Immature osteoblasts exhibit decreased intercellular communication in response to EMF but no change in Cx43. Here, we examined long term effects of pulsed EMF (PEMF) on MLO-Y4 osteocyte-like cells and ROS 17/2.8 osteoblast-like cells. In MLO-Y4 cell cultures, PEMF for 8 h/day for one, two or four days increased alkaline phosphatase activity but had no effect on cell number or osteocalcin. Transforming growth factor beta-1 (TGF-beta 1) and prostaglandin E(2) were increased, and NO(2-) was altered. PEMFs effect on TGF-beta1 was via a prostaglandin-dependent mechanism involving Cox-1 but not Cox-2. In ROS 17/2.8 cells, PEMF for 24, 48 or 72 h did not affect cell number, osteocalcin mRNA or osteocalcin protein. PEMF reduced Cx43 protein in both cells. Longer exposures decreased Cx43 mRNA. This indicates that cells in the osteoblast lineage, including well-differentiated osteoblast-like ROS 17/2.8 cells and terminally differentiated osteocyte-like MLO-Y4 cells, respond to PEMF with changes in local factor production and reduced Cx43, suggesting decreased gap junctional signaling.

Inhibition by eicosapentaenoic acid of IL-1beta-induced PGHS-2 expression in human microvascular endothelial cells: involvement of lipoxygenase-derived metabolites and p38 MAPK pathway

Prostaglandin H synthase 2 (PGHS-2), a highly inducible isoenzyme, is responsible for overproduction of the prostaglandins (PGs) in inflammatory sites. We established that among fish oil polyunsaturated fatty acids (PUFAs), eicosapentaenoic acid (EPA), but not docosahexaenoic acid (DHA), greatly decreased interleukin-1beta (IL-1beta)-induced PGHS-2 expression in human pulmonary microvascular endothelial cells (HPMECs). Lipoxygenase products 12 (S)-hydroperoxyeicosapentaenoic acid ((S)-HpEPE), 15 (S)-HpEPE and leukotriene (LT) D5 reproduced similar inhibitory effect, suggesting that they may be the intermediate metabolites responsible for PGHS-2 down-regulation by EPA. Accordingly, the EPA effect is prevented by nordihydroguaiaretic acid (NDGA) and by REV 5901, nonspecific and specific 5-lipoxygenase inhibitors, respectively. Besides, inhibition of cyclooxygenase activity by ibuprofen, indomethacin or aspirin was not able to prevent this effect. Moreover, cyclooxygenase metabolites of EPA (PGs D3, E3 and I3) markedly potentiate IL-1beta-induced PGHS-2 expression, probably by increasing intracellular cAMP levels. Peroxisome proliferator-activated receptors (PPARs) are known to be activated by fatty acids (FAs) such as EPA. We found here that HPMECs express only weak amounts of PPARalpha and PPARgamma whose activation by synthetic agonists, Wy-14,643 and ciglitazone, does not cause any inhibition of IL-1beta-induced PGHS-2 expression. This finding ruled out the involvement of PPARs in the EPA inhibitory effect. In addition, we established that EPA, which failed to inhibit nuclear factor-kappaB (NF-kappaB) activation, suppressed p38 mitogen-activated protein kinase (MAPK) phosphorylation in stimulated HPMECs. Our data demonstrate that EPA, unlike DHA, down-regulates PGHS-2 expression in HPMECs probably through its 5-lipoxygenase-dependent metabolites and advocates a beneficial role for this FA in limiting inflammatory response.

Lipoxygenase-catalyzed formation of R-configuration hydroperoxides

Prototypical lipoxygenases (LOXs) of animals and plants synthesize hydroperoxy fatty acids of the S stereoconfiguration, yet enzymes forming R-configuration products are found in both the animal and plant kingdoms. R-LOX are widespread in aquatic invertebrates, in some of which their R-HETE products have a defined role in reproductive function. A 12R-LOX has been found recently in humans and mice. The human 12R-LOX product, 12R-HETE, appears to be involved in the pathophysiology of psoriasis and other proliferative skin diseases; a role in normal skin development is implied from the spatial and temporal expression patterns of the 12R-LOX in the mouse embryo. In plants, there are few reports of R-LOX activity and in higher plants this is limited to enzymes that catalyze a significant degree of non-specific oxygenation. There are no obvious amino acid sequence motifs characterizing R-LOXs; and in the phylogenetic tree of the LOX superfamily, the R-LOXs do not group into a specific branch of genes. The mechanistic basis of stereocontrol over the oxygenation reaction performed by LOXs may relate to a changed binding orientation of the fatty acid substrate or to the direction of attack by molecular oxygen. A potentially relevant precedent for switching of R- and S-oxygenation specificity was described recently in studies of prostaglandin C-15 oxygenation during cycloxygenase catalysis; single amino acid changes can invert the oxygenation stereospecificity at C-15. In this case, the evidence suggests that R/S switching can occur with the substrate binding in the normal conformation.

The heart ofCiona intestinalis: eicosanoid-generating capacity and the effects of precursor fatty acids and eicosanoids on heart rate

Eicosanoids are a group of oxygenated fatty-acid derivatives formed from C20 polyunsaturated fatty acids including arachidonic and eicosapentaenoic acids. In mammals, these compounds have been shown to be key molecules in several physiological processes including regulation of the vascular system. This study determined whether eicosanoids or their precursors are involved in the regulation of heart rate in the sea squirt Ciona intestinalis. Eicosanoid generation by both heart and blood cells was measured. The major lipoxygenase products formed were both derivatives of eicosapentaenoic acid,namely 8- and 12-hydroxyeicosapentaenoic acids (8-HEPE and 12-HEPE). Smaller amounts of 8,15-dihydroxyeicosapentaenoic acid (8,15-diHEPE) were also formed. The cyclo-oxygenase product prostaglandin E was also found in small amounts in the heart. Isolated hearts were exposed either to these fatty acid precursors or to 8-HEPE, 12-HEPE or prostaglandin E3, and the effect on heart rate was recorded. Both eicosapentaenoic and arachidonic acids stimulated the heart rate at concentrations between 50 and 200 μmoll-1. 12-HEPE(5 μmoll-1) and prostaglandin E3 (50μmoll-1) caused a modest increase in heart rate, while 8-HEPE had no significant effects at any of the time periods studied (≤180 min). Overall, the results show that arachidonic and eicosapentaenoic acids have limited effects on heart rate and only at concentrations unlikely to be routinely liberated in vivo. Similarly, the eicosanoids tested had a minor stimulatory activity on heart rate. The potential mechanisms for this stimulation are discussed. Overall, these results suggest that such compounds are of limited importance in regulating the heart and vascular system of sea squirts.

Effects of 1alpha,25-(OH)(2)D(3) on rat growth zone chondrocytes are mediated via cyclooxygenase-1 and phospholipase A(2)

1alpha,25-(OH)(2)D(3) mediates its effects on growth zone chondrocytes via rapid membrane-associated events as well as through traditional nuclear receptor mechanisms. The membrane-associated signaling pathways include rapid production of diacylglycerol and activation of protein kinase C (PKC), as well as activation of phospholipase A(2) (PLA(2)), increased production of arachidonic acid, and increased production of prostaglandins. This study examined the roles of PLA(2) and cyclooxygenase (Cox) in the mechanism of action of 1alpha,25-(OH)(2)D(3) in these cells to determine whether one or both enzymes catalyze the rate limiting step and whether constitutive or inducible Cox is involved. Cultures were incubated with 1alpha,25-(OH)(2)D(3) for 9 min to measure PKC or for 24 h to measure physiological responses ([(3)H]-thymidine incorporation, alkaline phosphatase specific activity, [(35)S]-sulfate incorporation). Based on RT-PCR and Northern blot analysis, growth zone chondrocytes expressed mRNAs for both Cox-1 and Cox-2 and neither Cox was modulated by 1alpha,25-(OH)(2)D(3). To examine the role of Cox, the cultures were also treated with resveratrol (a specific inhibitor of Cox-1), NS-398 (a specific inhibitor of Cox-2), or indomethacin (a general Cox inhibitor). The results showed that Cox-1 inhibition reduced the 1alpha,25-(OH)(2)D(3)-dependent effects on proliferation, differentiation, and matrix production, whereas inhibition of Cox-2 only had an effect on proliferation. The effects of Cox inhibition were not rate limiting, based on experiments in which PLA(2) was activated with melittin or inhibited with quinacrine. However, at least part of the action of 1alpha,25-(OH)(2)D(3) was regulated by metabolism of arachidonic acid to prostaglandins. This supports the hypothesis that 1alpha,25-(OH)(2)D(3) exerts its effects via more than one signaling pathway and that these pathways are interrelated via the modulation of PLA(2) as a rate-limiting step. PKC regulation may occur at multiple stages in the signal transduction cascade. J. Cell. Biochem. Suppl. 36: 32-45, 2001.

Both cyclooxygenase-1 and cyclooxygenase-2 mediate osteoblast response to titanium surface roughness

Previous studies suggest that the enhanced expression of the osteoblastic phenotype exhibited by MG63 osteoblast-like cells on rough Ti surfaces (R(a) 4-5 microm) involves increased production of prostaglandin. Inhibition of prostaglandin synthesis by indomethacin blocks surface-roughness-dependent decreases in cell proliferation and increases in alkaline phosphatase activity and the production of osteocalcin and TGF-beta1. This study examined the hypothesis that the increase in expression of the osteoblastic phenotype noted in MG63 cells cultured on rough Ti surfaces is mediated by inducible cyclooxygenase-2 (Cox-2) whereas Cox-1 modulates prostaglandin production and phenotypic expression of the cells under standard conditions and on smooth Ti surfaces. MG63 cells were cultured on tissue culture plastic, smooth Ti (PT, R(a) = 0.60 microm), and two rough Ti surfaces with differing morphologies (SLA, R(a) = 3.97 microm and TPS, R(a) = 5.21 microm). At 24 h after plating, media were replaced with media containing the general Cox inhibitor indomethacin (10(-7)M), the Cox-1 inhibitor resveratrol (1 or 10 microM), or the Cox-2 inhibitor NS-398 (1 or 10 microM). Media were changed again after 48 h. Five days after plating, osteocalcin, PGE(2), and TGF-beta1 content of the conditioned media were determined. Cell numbers were assessed in the same cultures used for determination of osteocalcin production. Cell layer protein and alkaline phosphatase specific activity were assessed in cultures used to measure PGE(2) and TGF-beta1. Indomethacin, resveratrol, and NS-398 had no effect on cell number. Indomethacin blocked the surface-roughness-dependent increase in PGE(2) production by up to 80%. Similarly, resveratrol inhibited up to 50% of the PGE(2) production on smooth surfaces and up to 80% on rough surfaces. In contrast, NS-398 had no effect on PGE(2) production by cells on smooth surfaces but caused a 60% reduction in cultures on rough surfaces. Indomethacin reduced alkaline phosphatase on all surfaces below basal levels. However, neither resveratrol nor NS-398 had an effect. Indomethacin blocked the stimulatory effect of surface roughness on osteocalcin production while resveratrol only partially reduced osteocalcin production, and NS398 completely blocked the surface-dependent increase. TGF-beta1 production on rough surfaces was blocked by indomethacin. The effects of resveratrol and NS-398 were dose dependent, but neither agent caused total inhibition of the increase noted on SLA, and only resveratrol blocked the increase on TPS. These results indicate that both Cox-1 and Cox-2 are involved in the response of osteoblasts to surface roughness with respect to production of PGE(2), TGF-beta1, and osteocalcin. While prostaglandin mediates the effects of surface roughness on alkaline phosphatase, neither Cox-1 nor Cox-2 appears to be involved, at least with respect to the two inhibitors used.

Activation of prostacyclin synthesis by mechanical stimulation in the ciliated protozoan Tetrahymena thermophila

We detected a HPLC peak corresponding to 6-keto-PGF(1alpha), a stable metabolite of prostacyclin (PGI(2)), in [1-(14)C]arachidonate metabolites from the ciliated protozoan Tetrahymena thermophila. Quantitative analysis of 6-keto-PGF(1alpha) by enzyme immunoassay revealed that the synthesis and release were rapidly activated by the mechanical stimulation of a short centrifugation. The activation was suppressed significantly by a cyclooxygenase inhibitor, ibuprofen, and was independent of the extracellular Ca(2+). External addition of PGI(2) and its stable analogue, beraprost, caused a transient increase in the tumbling frequency of swimming. Other prostanoids, PGE(2) and PGF(2alpha), have no effect on the swimming. These results indicate that a free-living ciliate, T. thermophila, synthesizes and has a specific sensitivity to PGI(2).

Discovery of an 11 (R)- and 12(S)-lipoxygenase activity in ovaries of the mussel Mytilus edulis

Eicosanoid biosynthesis was investigated in mussel gonads by incubation of tissue homogenates with radiolabeled arachidonic acid and analysis of the products by radio-high-performance liquid chromatography. No radiolabeled metabolites were formed in homogenates of testes, but two major metabolites were synthesized by ovarian preparations. The radiolabeled metabolites were analyzed by mass spectrometry and chiral chromatography and identified as 11 (R)-hydroxy-5,8,1 2,14-eicosatetraenoic acid and 12(S)-hydroxy-5,8,10,14-eicosatetraenoic acid. In addition, four other nonlabeled metabolites, formed from endogenous substrates, were detected in ovarian extracts. Their structures, determined by mass spectrometric analysis, were the corresponding 11- and 12-hydroxy analogs formed from eicosapentaenoic acid (11-HEPE and 12-HEPE) and 9-hydroxy-6,10,12,15-octadecatetraenoic acid (9-HOTE) and 13-hydroxy-6,9,11,15-octadecatetraenoic acid formecl from stearidonic acid. The biosynthesis of the 11 - and 12-hydroxy products was calcium dependent, localized to the 100,000 x g supernatant cell fraction, and was inhibited by nordihydroguaiaretic acid, but not inhibited by the prostaglandin synthase inhibitors aspirin and indomethacin, or the monoxygenase inhibitor proadifen. Together these data suggested that both the 11 (R)- and 12(S)-hydroxy products were formed from lipoxygenase-type enzymes. Incubation of homogenates of immature ovaries with eicosapentaenoic acid revealed the major product to be I2-HEPE, whereas in mature ovaries mainly 11-HEPE was formed. Extraction of spawned eggs with methanol revealed that predominantly 11-HEPE and 9-HOTE were formed from endogenous substrates. This study shows that female gonads of the mussel express an 11(R)- and 12(S)-lipoxygenase activity whose expression is dependent on differentiation of the ovary.