Prostaglandin biosynthesis and subcellular localization of prostaglandin H synthase activity in the lone star tick, Amblyomma americanum

Mediated effect of ultrasound treated Diclofenac on mussel hemocytes: First evidence for the involvement of respiratory burst enzymes in the induction of DCF-mediated unspecific mode of action

The present study investigates the toxic behavior of diclofenac (DCF) before and after its ultrasound (US) treatment, as well as the involvement of intracellular target molecules, such as NADPH oxidase and NO synthase, in the DCF-induced adverse effects on hemocytes of mussel Mytilus galloprovincialis. In this context, appropriate volumes (350 and 500mL) of DCF solutions (at concentrations of 2, 2.5, 5 and 10mgL(-1)) were treated under different ultrasound operating conditions (frequency at 582 and 862kHz, electric power density at 133 and 167W) for assessing US method efficiency. In parallel, DCF and US DCF-mediated cytotoxic (in terms of cell viability measured with the use of neutral red uptake/NRU method), oxidative (in terms of superoxide anions/(.)O2(-), nitric oxides such as NO2(-) and lipid peroxidation products, such as malondialdehyde/MDA content) and genotoxic (DNA damage measured by the use of Comet assay method) effects were investigated in hemocytes exposed for 1h to 5, 10 and 100ngL(-1) and 1, 10 and 20μgL(-1) of DCF. The involvement of NADPH oxidase and NO synthase to the DCF-induced toxicity was further investigated by the use of 10μΜ L-NAME, a NO synthase inhibitor and 10μΜ DPI, a NADPH oxidase inhibitor. According to the results, 350mL of 2mgL(-1) DCF showed higher degradation (>50%) under 167W electric power density and frequency at 862kHz for 120min, compared to degradation in all other cases, followed by a significant elimination of its toxicity. Specifically, US DCF-treated hemocytes showed a significant attenuation of DCF-mediated cytotoxic, oxidative and genotoxic effects, which appeared to be caused by NADPH oxidase and NO synthase activation, since their inhibition was followed by a significant elimination of (.)O2(-) and NO2(-) generation and the concomitant oxidative damage within cells. The results of the present study showed for the first time that unspecific mode of action of DCF, associated with the induction of NADPH oxidase and NO synthase in mussel hemocytes, could be significantly diminished after partial US degradation of DCF, at least under optimized operating conditions currently tested.

Insights into the prostanoid pathway in the ovary development of the penaeid shrimp Penaeus monodon

The prostanoid pathway converts polyunsaturated fatty acids (PUFAs) into bioactive lipid mediators, including prostaglandins, thromboxanes and prostacyclins, all of which play vital roles in the immune and reproductive systems in most animal phyla. In crustaceans, PUFAs and prostaglandins have been detected and often associated with female reproductive maturation. However, the presence of prostanoid biosynthesis genes remained in question in these species. In this study, we outlined the prostanoid pathway in the black tiger shrimp Penaeus monodon based on the amplification of nine prostanoid biosynthesis genes: cytosolic phospholipase A2, hematopoietic prostaglandin D synthase, glutathione-dependent prostaglandin D synthase, prostaglandin E synthase 1, prostaglandin E synthase 2, prostaglandin E synthase 3, prostaglandin F synthase, thromboxane A synthase and cyclooxygenase. TBLASTX analysis confirmed the identities of these genes with 51-99% sequence identities to their closest homologs. In addition, prostaglandin F2α (PGF2α), which is a product of the prostaglandin F synthase enzyme, was detected for the first time in P. monodon ovaries along with the previously identified PUFAs and prostaglandin E2 (PGE2) using RP-HPLC and mass-spectrometry. The prostaglandin synthase activity was also observed in shrimp ovary homogenates using in vitro activity assay. When prostaglandin biosynthesis was examined in different stages of shrimp ovaries, we found that the amounts of prostaglandin F synthase gene transcripts and PGF2α decreased as the ovaries matured. These findings not only indicate the presence of a functional prostanoid pathway in penaeid shrimp, but also suggest a possible role of the PGF2α biosynthesis in shrimp ovarian development.

Tick salivary prostaglandins: Presence, origin and significance

Prostaglandins (PGs) are oxygenated metabolites of polyunsaturated fatty acids, most notably arachidonic acid, that act as 'local hormones', regulating a plethora of physiological processes in mammals and other vertebrates. For a long time, PGs were reported only in higher vertebrates, but more recently they have been reported in lower organisms such as bacteria, yeasts and protozoa, and much information is now available on PGs in insects. Prostaglandins are increasingly reported to exist at the host-parasite interface and are thought to aid the parasite by modulating the inflammatory and immune response. Ticks secrete saliva containing extremely high concentrations of PGs into the host, and in this article Alan Bowman, Jack Dillwith and John Sauer provide a synopsis of the information, to date, on the presence, synthesis and proposed roles for these tick salivary PGs.

Prostaglandin biosynthesis by fat body from larvae of the beetle Zophobas atratus

We describe prostaglandin (PG) biosynthesis by microsomal-enriched fractions of fat body prepared from larvae of the tenebrionid beetle, Zophobas atratus. PG biosynthesis was sensitive to incubation time, temperature, pH, substrate and protein concentration. Optimal PG biosynthesis conditions of those we examined included 2 mg of microsomal-enriched protein, incubated at 22 degrees C for 2 min at pH 6. These preparations yielded four major PGs: PGA(2), PGE(2), PGD(2) and PGF(2 alpha). PGA(2) and PGF(2 alpha) were the predominant eicosanoids produced under these conditions. Two non-steroidal anti-inflammatory drugs, indomethacin and naproxen, effectively inhibited PG biosynthesis in low concentrations. In vitro PG biosynthetic reaction conditions, using vertebrate or invertebrate enzyme sources, usually include a cocktail of reaction co-factors. The Z. atratus preparation similarly performs better in the presence of co-factors. Arch.

Eicosanoids mediate nodulation reactions to bacterial infections in adults of two 17-year periodical cicadas, Magicicada septendecim and M. cassini

Nodulation is the first and quantitatively most important cellular defense reaction to bacterial infections in insects. Treating adults of the 17-year periodical cicadas, Magicicada septendecim and M. cassini, with eicosanoid biosynthesis inhibitors immediately prior to intrahemocoelic injections of the bacterium, Serratia marcescens, sharply reduced the nodulation response to bacterial challenges. Separate treatments with specific inhibitors of phospholipase A(2), cyclooxygenase, and lipoxygenase reduced nodulation, supporting our view that nodule formation is a multi-step process in which individual steps are separately mediated by lipoxygenase and cyclooxygenase products. The inhibitory influence of dexamethasone was apparent by 2 h after injection, and nodulation was significantly reduced, relative to control insects, over the following 14 h. The dexamethasone effects were reversed by treating bacteria-challenged insects with the eicosanoid-precursor polyunsaturated fatty acid, arachidonic acid. Low levels of arachidonic acid were detected in fat body phospholipids. These findings in adults of an exopterygote insect species with an unusual life history pattern broaden our hypothesis that eicosanoids mediate cellular immune reactions to bacterial infections in most, if not all, insects.

Prostaglandin biosynthesis by salivary glands isolated from the lone star tick, Amblyomma americanum

Salivary glands separated from internal tissues of the lone star tick, Amblyomma americanum, are competent to synthesize prostaglandins (PGs). Using an in vitro PG biosynthesis assay four major PGs, namely, PGA2/PGB2, PGD2, PGE2, and PGF2 alpha were synthesized. Under standard assay conditions PGA2/PGB2 was the predominant product. Salivary tissues as well as non-salivary internal tissues were capable of PG biosynthesis. We observed that storing ticks at -80 degrees C for 3 months resulted in reduced PG biosynthesis. This indicates that the tick preparation, unlike comparable mammalian preparations, is not stable to freezing. Cyclooxygenase inhibitors, indomethacin (> 10 microns) and naproxen (> 15 microns), completely inhibited PG biosynthesis. These results demonstrate the presence of a PG biosynthetic system in salivary glands and other internal tissues of the lone star ticks.

Eicosanoids mediate microaggregation and nodulation responses to bacterial infections in black cutworms, Agrotis ipsilon, and true armyworms, Pseudaletia unipuncta

Nodulation is the first, and quantitatively predominant, cellular defense reaction to bacterial infection in insects and other invertebrates. Inhibition of eicosanoid biosynthesis in true armyworms, Pseudaletia unipuncta, and black cutworms, Agrotis ipsilon, immediately prior to intrahemocoelic injections with heat-killed preparations of the bacterium, Serratia marcescens, severely impaired the nodulation response. Five eicosanoid biosynthesis inhibitors, including dexamethasone (a phospholipase A(2) inhibitor), indomethacin, ibuprofen (cyclooxygenase inhibitors), phenidone (dual lipoxygenase/cyclooxygenase inhibitor) and eicosatetraynoic acid (an arachidonic acid analog that inhibits all arachidonic acid metabolism) severely reduced nodulation in infected insects. The dexamethasone effects were reversed by treating true armyworms with arachidonic acid immediately after infection. In addition to these pharmacological findings, we demonstrate that an eicosanoid biosynthesis system is present in these insects. Arachidonic acid is present in fat body phospholipids at about 0.4% of total phospholipid fatty acids. Fat body expressed a phospholipase A(2) that can hydrolyze arachidonic acid from the sn-2 position of cellular phospholipids. Fat body preparations were competent to biosynthesize prostaglandins, of which PGE(2) was the major product. These findings support the hypothesis that eicosanoids mediate cellular immune reactions in insects.

What can we learn from prostaglandins and related eicosanoids in insects?

Eicosanoids are oxygenated metabolites of three C20 polyunsaturated fatty acids (20:3n-6, 20:4n-6, and 20:5n-3). While eicosanoids are very well known in mammalian systems, mostly due to their pharmaceutical interest, there is increasing recognition of the significance of these compounds in insects and other invertebrates. In this paper we consider four major concepts emerging from work on eicosanoids in invertebrates. First, the biological significance of eicosanoids extends far beyond their physiological and pathophysiological actions in human and veterinary medicine. Second, we can greatly improve our understanding of eicosanoids in insects by integrating our work on insects into ongoing studies of other invertebrates. Third, some eicosanoid actions may be fundamental to animals. Fourth, the biochemistry of eicosanoids in insects and other invertebrates can differ from expectations based on the mammalian background. Finally, we point to an uncharted frontier in insect studies--the biochemical mechanisms of eicosanoid action--by drawing attention to some of the work on eicosanoid receptors in mammalian systems.