Lipoxin formation in fish leucocytes

Functional Characterization of Novel Bony Fish Lipoxygenase Isoforms and Their Possible Involvement in Inflammation

Eicosanoids and related compounds are pleiotropic lipid mediators, which are biosynthesized in mammals via three distinct metabolic pathways (cyclooxygenase pathway, lipoxygenase pathway, epoxygenase pathway). These mediators have been implicated in the pathogenesis of inflammatory diseases and drugs interfering with eicosanoid signaling are currently available as antiphlogistics. Eicosanoid biosynthesis has well been explored in mammals including men, but much less detailed information is currently available on eicosanoid biosynthesis in other vertebrates including bony fish. There are a few reports in the literature describing the expression of arachidonic acid lipoxygenases (ALOX isoforms) in several bony fish species but except for two zebrafish ALOX-isoforms (zfALOX1 and zfALOX2) bony fish eicosanoid biosynthesizing enzymes have not been characterized. To fill this gap and to explore the possible roles of ALOX15 orthologs in bony fish inflammation we cloned and expressed putative ALOX15 orthologs from three different bony fish species (N. furzeri, P. nyererei, S. formosus) as recombinant N-terminal his-tag fusion proteins and characterized the corresponding enzymes with respect to their catalytic properties (temperature-dependence, activation energy, pH-dependence, substrate affinity and substrate specificity with different polyenoic fatty acids). Furthermore, we identified the chemical structure of the dominant oxygenation products formed by the recombinant enzymes from different free fatty acids and from more complex lipid substrates. Taken together, our data indicate that functional ALOX isoforms occur in bony fish but that their catalytic properties are different from those of mammalian enzymes. The possible roles of these ALOX-isoforms in bony fish inflammation are discussed.

Can a fibular malunion be corrected by a Z-shaped fibular osteotomy?

BACKGROUND

The aim of this study was to assess the short-term clinical and radiographic outcomes in patients who underwent realigning Z‑shaped fibular osteotomy.

METHODS

Between January 2007 and December 2014, 28 patients with a painful fibular malunion underwent a Z-shaped realignment fibular osteotomy. The mean age was 42.2 ± 14.1 years (range 19.1-67.8 years) and the mean follow-up was 7.0 ± 1.7 years (range 4.0-9.7 years), with no loss to follow-up. Weight-bearing radiographs were used to determine the distal fibula alignment based on Weber's criteria. Degenerative changes of the tibiotalar joint were assessed using the Kellgren-Lawrence scale. Clinical assessment included pain evaluation, measurement of ankle range of motion (ROM), sports activities, and quality of life outcomes.

RESULTS

There were no intraoperative or perioperative complications. No delayed unions or nonunions were observed. One patient had radiographic progression of degenerative changes in the tibiotalar joint. Postoperative complications included removal of hardware (n = 15) and arthroscopic tibiotalar joint debridement (n = 2). At the last follow-up the mean visual analog scale (VAS) decreased from 6.5 ± 1.1 to 2.1 ± 1.1 (p < 0.001),the ROM improved from 39º ± 6º to 45º ± 4.5º (p < 0.001), the short form health survey questionnaire (SF-36) physical and mental outcome scores improved from 49 ± 8 to 84 ± 7 (p < 0.001) and from 61 ± 4 to 83 ± 5 (p < 0.001), respectively.

CONCLUSION

The Z‑shaped realignment osteotomy of the distal fibula can provide pain relief and functional improvement in the treatment of fibular malunion. Further studies are needed to address long-term outcomes in this patient cohort.

Identification of resolvin D2 receptor mediating resolution of infections and organ protection

Chiang et al. identify GPR18 as a novel receptor for resolvin D2, and show that activation of this receptor in human and mouse phagocytes stimulates phagocytic clearance during bacterial infections and promotes organ protection

Endogenous mechanisms that orchestrate resolution of acute inflammation are essential in host defense and the return to homeostasis. Resolvin (Rv)D2 is a potent immunoresolvent biosynthesized during active resolution that stereoselectively stimulates resolution of acute inflammation. Here, using an unbiased G protein–coupled receptor-β-arrestin–based screening and functional sensing systems, we identified a receptor for RvD2, namely GPR18, that is expressed on human leukocytes, including polymorphonuclear neutrophils (PMN), monocytes, and macrophages (MΦ). In human MΦ, RvD2-stimulated intracellular cyclic AMP was dependent on GPR18. RvD2-stimulated phagocytosis of Escherichia coli and apoptotic PMN (efferocytosis) were enhanced with GPR18 overexpression and significantly reduced by shRNA knockdown. Specific binding of RvD2 to recombinant GPR18 was confirmed using a synthetic ³H-labeled-RvD2. Scatchard analysis gave a K_d of ∼10 nM consistent with RvD2 bioactive concentration range. In both E. coli and Staphylococcus aureus infections, RvD2 limited PMN infiltration, enhanced phagocyte clearance of bacteria, and accelerated resolution. These actions were lost in GPR18-deficient mice. During PMN-mediated second organ injury, RvD2’s protective actions were also significantly diminished in GPR18-deficient mice. Together, these results provide evidence for a novel RvD2–GPR18 resolution axis that stimulates human and mouse phagocyte functions to control bacterial infections and promote organ protection.

The evolution of inflammatory mediators

Invertebrates do not display the level of sophistication in immune reactivity characteristic of mammals and other 'higher' vertebrates. Their great number and diversity of forms, however, reflect their evolutionary success and hence they must have effective mechanisms of defence to deal with parasites and pathogens and altered self tissues. Inflammation appears to be an important first line defence in all invertebrates and vertebrates. This brief review deals with the inflammatory responses of invertebrates and fish concentrating on the cell types involved and the mediators of inflammation, in particular, eicosanoids, cytokines and adhesion molecules.

Resolution phase of inflammation: novel endogenous anti-inflammatory and proresolving lipid mediators and pathways

Resolution of inflammation and the return of tissues to homeostasis are essential. Efforts to identify molecular events governing termination of self-limited inflammation uncovered pathways in resolving exudates that actively generate, from essential omega fatty acids, new families of local-acting mediators. These chemical mediator families, termed resolvins and protectins, are potent stereoselective agonists that control the duration and magnitude of inflammation, joining the lipoxins as signals in resolution. This review examines the mapping of these circuits and recent advances in our understanding of the biosynthesis and actions of these novel proresolving lipid mediators. Aspirin jump-starts resolution by triggering biosynthesis of specific epimers of these mediators. In addition to their origins in inflammation resolution, these compounds also display potent protective roles in neural systems, liver, lung, and eye. Given the potent actions of lipoxins, resolvins, and protectins in models of human disease, deficiencies in resolution pathways may contribute to many diseases and offer exciting new potential for therapeutic control via resolution.

Emerging roles for cyclooxygenase-2 in gastrointestinal mucosal defense

The development of selective inhibitors of cyclooxygenase-2 (COX-2) was based on the concept that this enzyme played little, if any, role in modulating the ability of the gastrointestinal (GI) tract to resist and respond to injury. There is now overwhelming evidence that this is far from true. Indeed, COX-2 mediates several of the most important components of 'mucosal defense', contributes significantly to the resolution of GI inflammation and plays a crucial role in regulating ulcer healing. COX-2 also contributes to long-term changes in GI function after bouts of inflammation.

Possible role of LTB4 in the antiviral activity of turbot (Scophthalmus maximus) leukocyte-derived supernatants against viral hemorrhagic septicemia virus (VHSV)

Turbot (Scophthalmus maximus) blood leukocyte-derived supernatants were tested for antiviral activity against viral hemorrhagic septicemia virus (VHSV). The assays were performed by quantifying the effect of the supernatants on the replication of VHSV in the rainbow trout (Oncorhynchus mykiss) cell line, RTG-2. Supernatants were obtained by incubating the leukocytes for 17 h at 18 degrees C in L-15 medium supplemented with 5% fetal calf serum (FCS). Testing of leukocyte supernatants indicated that antiviral activity against VHSV resulted in a viral titer reduction of 72.1%. After the supernatants were extracted with calcium ionophore A23187 treatment, the antiviral activity significantly increased, resulting in a viral titer reduction of 99.9%. In order to determine the nature of this antiviral activity, supernatants were produced from leukocytes treated for 17 h with inhibitors of eicosanoid biosynthesis, reactive oxygen intermediates and nitric oxide (NO) production. None of the inhibitors significantly suppressed the supernatant antiviral activity. The presence of oxygen radicals and NO was measured in the case of co-cultures of leukocytes and RTG-2 cells, but no significant differences were found in the VHSV-infected co-cultures compared to non-infected controls. Since previous work demonstrated that leukotriene B4 (LTB4) was present in turbot blood leukocyte-derived supernatants, we assessed the effect of the VHSV in vitro infection on turbot leukocyte LTB4 production by high performance liquid chromatography (HPLC). The levels of LTB4 were significantly increased in the supernatants after VHSV infection. Furthermore, exogenous LTB4 significantly inhibited VHSV replication in RTG-2 cells. These findings suggest that LTB4 may play a significant role in VHSV replication.

Production of leukotriene B4 and prostaglandin E2 by turbot (Scophthalmus maximus) leukocytes

Production of two eicosanoids derived from lipoxygenase and cyclooxygenase activities: leukotriene B4 (LTB4) and prostaglandin E2 (PGE2), respectively, have been simultaneously determined in turbot (Scophthalmus maximus) blood leucocyte and kidney macrophage supernatants by a reverse phase high performance liquid chromatography (HPLC) system coupled with a Diode-Array detector. Levels of LTB4 after calcium ionophore challenge were 4.08 ng ml-1 in blood leukocyte supernatants and 0.25 ng ml-1 in kidney macrophage supernatants. The levels found for PGE2 were 428.23 and 606.67 ng ml-1 in blood leukocytes and kidney macrophage supernatants, respectively. When blood leukocytes were treated with the respective inhibitors for the enzymes implicated on the synthesis of both compounds an inhibition of 90.35% was observed for PGE2 and 76.44% for LTB4. The detection limit of the method was 0.15 ng ml-1 for LTB4 and 50 ng ml-1 for PGE2.

Prostanoid synthesis in whole blood cells from fish of the Arabian Gulf

The ability to synthesise prostaglandins and thromboxane from 14C-labelled arachidonic acid was investigated in 11 species of fish from the Arabian Gulf. Cyclooxygenase activity was assessed in washed whole blood cells. Arachidonic acid and its metabolites were extracted and separated on silicic acid columns and thin layer chromatography (silica gel G). Total capacity to convert [14C]arachidonic acid to prostanoids varied from 1 to 35% among the 11 fish species studied. Gray shark (Chiloscyllium griseum) blood cells had the highest capacity (37 +/- 0.4%) to convert arachidonate into prostanoids and two species of catfish (Arius bilineatus and A. thalassinus) exhibited greater than 10% capacity to convert [14C]arachidonate into prostanoids. The major prostanoid synthesised by the two catfish (A. bilineatus and A thalassinus) was 6-keto PGF1 alpha, a stable metabolite of prostacyclin, PGI2. In contrast, A. teunispinis synthesised thromboxane B2, a stable metabolite of thromboxane A2. Thromboxane B2 (TXB2) was the major product synthesised by all three species of shark studied (Chil. griseum, Carcharhinus plumbeus, Carch. melanopterus), with 6-keto PGF1 alpha a minor product. Other fish studied showed a varied pattern of prostanoid synthesis. The synthesis of these prostanoids was almost completely blocked by preincubation of the whole blood cells from catfish and shark with indomethacin (0.5 microM) suggesting the involvement of cyclooxygenase-mediated prostanoid synthesis.

Eicosanoid synthesis by purified thrombocytes and erythrocytes from warm- and cold-acclimated American bullfrogs (Rana catesbeiana)

Amphibian blood plays an important role in eicosanoid synthesis. Although clotting frog blood produces eicosanoids, the cellular source of prostaglandins and thromboxanes in bullfrog blood is unknown. Thromboxane (TX)B2 synthesis from purified thrombocytes was affected by 30-day cold-acclimation at 5 degrees, but not PGE2 or leukotriene (LT) synthesis. Although no cyclooxygenase activity has been found in human erythrocytes, frog erythrocytes were capable of forming cyclooxygenase products, but the amounts were lower than those produced by thrombocytes. Additionally, there was no effect of cold exposure on eicosanoid production by isolated erythrocytes. Similar to some mammalian nucleated white blood cells, nucleated bullfrog thrombocytes and erythrocytes produced leukotrienes. The production of eicosanoids by thrombocytes was stimulated by A23187 and thrombin. Erythrocytes were stimulated by A23187. Control synthesis by erythrocytes and thrombocytes was inhibited by 5 microM indomethacin (cyclooxygenase pathway) or nordihydroguaiaretic acid (5-lipoxygenase pathway) and cyclooxygenase products were increased in the presence of nordihydroguaiaretic acid. Thrombin stimulation of eicosanoid production by thrombocytes was inhibited when the inhibitors were present prior to the final centrifugation of the cell isolation. The results suggest that cold exposure can affect eicosanoid synthesis in thrombocytes, but not erythrocytes, and that thrombocytes are a major source of eicosanoids in bullfrogs. The production of cyclooxygenase and lipoxygenase products by nucleated erythrocytes and thrombocytes suggests a role for these compounds in hemostasis and inflammatory responses in these animals.

Biosynthesis of thromboxane by snake (Elaphe obsoleta) erythrocytes and the requirement of eicosanoid production for blood clotting

Lower vertebrates provide important insights into the evolution of eicosanoid synthesis and function. Whole snake blood, purified nucleated erythrocytes, and isolated leukocytes activated by clotting or A23187 produced thromboxane, PGE2, and 5-lipoxygenase products. Indomethacin's complete inhibition of clotting suggests eicosanoids produced by these cells are important in snake blood hemostasis.

Lipoxins and novel aspirin-triggered 15-epi-lipoxins (ATL): a jungle of cell-cell interactions or a therapeutic opportunity?

Lipid-derived mediators play critical roles in inflammation and other multicellular vascular processes, including atherosclerosis and thrombosis. The lipoxins (LXs) were first isolated in 1984, and have continued to show intriguing and potentially important biological roles. These compounds carry a trihydroxytetraene structure and are both structurally and functionally unique among arachidonic acid-derived bioactive products. The availability of synthetic materials for evaluation of bioactions as well as appropriate methods of detection to determine when and where LX are generated has, in recent studies, catapulted our understanding of the formation and actions of the lipoxins. This mini-review addresses new concepts in the formation and biological roles of these lipid-derived mediators and considers whether the lipoxins and the newly discovered aspirin-triggered lipoxins (ATL) represent novel approaches for therapeutic opportunities. Recent findings indicate that select cytokines and aspirin initiate and regulate LX biosynthetic events. These circuits involve cell-cell interfacing that facilitates transcellular events to form LX that display anti-inflammatory actions in both in vitro and in vivo models. These recent results suggest that LX biosynthetic circuits assemble to evoke anti-inflammatory actions and generate LX that can serve as "stop signals" in appropriate microenvironments.

5(S),15(S)-dihydroxyeicosatetraenoic acid and lipoxin generation in human polymorphonuclear cells: dual specificity of 5-lipoxygenase towards endogenous and exogenous precursors

5-Lipoxygenase activation of human blood polymorphonuclear cells (PMN) from asthmatic patients (asthmatics) was studied to investigate whether differences may exist with healthy subjects (controls). The respective cell capacities to produce lipoxins (LXs), leukotrienes, and 5(S), 15(S)-dihydroxyeicosatetraenoic acid [5(S),15(S)-diHETE] were compared under in vitro stimulation by ionophore A23187, with or without exogenous 15(S)-hydroxyeicosatetraenoic acid [15(S)-diHETE]. Eicosanoids were analyzed by elution with an isocratic reverse-phase high performance liquid chromatography system, and their profiles, detected by simultaneous monitoring at 302, 280, and 246 nm, were evaluated on the basis of chromatographic behavior: UV spectral characteristics and coelution with synthetic standards. In the presence of exogenous 15(S)-HETE, human PMN were able to produce LXs and 5(S),15(S)-diHETE, PMN from asthmatics were able to produce 5(S), 5(S),15(S)-diHETE, and LXs from endogenous sources, whereas in the same experimental conditions, no detectable amounts of these compounds were released by PMN from controls. The levels of 5(S),15(S)-diHETE, and LXs biosynthesized from endogenous arachidonic acid were highly correlated. Two different LX patterns were observed involving two possible metabolic pathways: (a) via the intermediate 5,6-epoxytetraene alone for LXs generation from exogenous 15(S)-HETE; and (b) via 5,6- and/or 14,15-epoxytetraenes leading to the formation of an enzyme-bound delocalized carbocation for LXs generation from endogenous arachidonate, respectively. The enhanced 5-lipoxygenase activation of blood PMN from asthmatics and the metabolism of exogenous 15(S)-HETE may reflect a priming induced by various mediators released from environmental cells, and could be considered as a model of transcellular signalization between PMN and endothelial cells.

Eicosanoid generating capacities of different tissues from the rainbow trout, Oncorhynchus mykiss

The eicosanoid generating potential of the brain, gills, skin, ovary, muscle, eye, liver, spleen, heart, and alimentary canal in the rainbow trout, Oncorhynchus mykiss, was examined. All the organs/tissues examined synthesized the 12-lipoxygenase products, 12-hydroxyeicosatetraenoic acid (12-HETE), and 12-hydroxyeicosapentaenoic acid (12-HEPE), implying the widespread nature of this enzyme in trout. Both prostaglandin E and LTC were also found in variable amounts in the organs, with the greatest amount of PGE found in the gill. Leukotriene (LT) B4 and LTB5 were found in supernatants from calcium ionophore-challenged brain, skin, ovary, liver, spleen, and heart, but the lipoxins A4 and A5 were only present in brain, ovary, and spleen in relatively small amounts. As lipoxins have previously been shown to be synthesized by macrophages in rainbow trout [Pettitt et al., J. Biol. Chem. 266, 8720-8726 (1991)], and related cells (microglial cells) are found in the brain of mammals, the localization of macrophage-like cells in trout brain was investigated immunocytochemically. Monoclonal antibodies specific for trout leucocytes failed to identify any microglial-like cells in sections of the brain, although microvessels containing immuno-positive reaction products were observed. A number of distinct lipoxygenase products were found in supernatants of ionophore-challenged gill, including 14-hydroxydocosahexaenoic acid, 12-HETE, and 12-HEPE, and a large number of dihydroxy fatty acid derivatives with conjugated triene chromophores. One of these products was tentatively identified as 8(R),15(S)-dihydroxyeicosatetraenoic acid, a dual 12- and 15-lipoxygenase product, but apparently no LTB4 was generated by this tissue.

Eicosanoid generation and effects on the aggregation of thrombocytes from the rainbow trout, Oncorhynchus mykiss

Fish blood lacks anucleate platelets but contains a nucleated cell type termed the thrombocyte that is thought to be functionally analogous. Thrombocytes were purified from the peripheral blood of the rainbow trout, Oncorhynchus mykiss, by a two step gradient centrifugation method. Following this procedure, the recovered thrombocytes were 78-86% pure as defined by immunoreactivity to a panel of monoclonal antibodies and were of variable morphology from round to spindle-shaped. Incubation of thrombocyte suspensions with either calcium ionophore, A23187, platelet-activating factor or a thromboxane (TX) mimetic, U-46619, generated a range of eicosanoids derived from arachidonic acid including 12-hydroxyeicosatetraenoic acid (12-HETE), TXB2, prostaglandin (PG) E2, leukotriene (LT) B4 and lipoxin (LX) A4. The equivalent products derived from eicosapentaenoic acid were also formed. Co-incubation of thrombocytes with either erythrocytes or granulocytes/monocytes in the presence of calcium ionophore did not result in the formation of any further new lipoxygenase products. Incubation of isolated thrombocytes in plasma-free conditions with U-46619 (0.03-10 microM) resulted in a rapid, dose-dependent aggregatory response. This effect was markedly augmented in the presence of mammalian fibrinogen (400 micrograms ml-1). Thrombin (0.1-1.3 units ml-1), like U-46619, was also a potent proaggregatory compound for trout thrombocytes. LXA4 and LTB4 had limited aggregatory potential and then only at high concentrations (10 microM), while 12-HETE and PAD had no significant effect at all concentrations tested. These results demonstrate that some of the eicosanoids released during the activation of trout thrombocytes are involved in the aggregatory behaviour of this cell type.