Eicosanoid-precursor Polyunsaturated Fatty Acid Research Articles

Eicosanoids Act in Nodulation Reactions to Bacteria Serratia Marcescensin Hemipteran Pest, Eurygaster Integriceps

In insects, nodulation is the first step in cellular defense reactions to bacterial, fungal, and some viral infections. The hypothesis was posed that the hemipteran pest E. integriceps produces melantoic nodulation reactions to bacterial challenge and that eicosanoids mediate these reactions. Treating the adult of E. integriceps with Serratia marcescens induced nodulation reactions in a challenge dose-dependent manner. Injecting the adult E. integriceps with eicosanoid biosynthesis inhibitors, immediately before intrahemocoelic injections of the bacterium Serratia marcescens, sharply reduced the nodulation response to bacterial challenges. Separate treatments with specific inhibitors including dexamethasone (a phospholipase A_2 inhibitor), indomethacin, naproxen, ibuprofen, piroxicam (cyclooxygenase inhibitors), esculetin (a lipoxygenase inhibitor), and phenidone (dual cyclooxgenase/lipoxygenase inhibitor) also impaired the ability of E. integriceps to form nodules in reaction to bacterial challenge. The inhibitory influence of ibuprofen was apparent within 30 min after infection, and nodulation was significantly reduced, relative to control insects, over the following 4 h. Increasing ibuprofen dosages were associated with decreasing nodulation activity. The dexamethasone effects were reversed by treating bacteria-injected insects with the eicosanoid-precursor polyunsaturated fatty acid, arachidonic acid. These findings support the hypothesis that eicosanoids also act in nodulation reactions to bacterial infections in the hemipteran pest E. integriceps.

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.

Eicosanoids mediate nodulation reactions to bacterial infections in larvae of the butterfly, Colias eurytheme

Nodulation is the first, and qualitatively predominant, cellular defense reaction to bacterial infections in insects. Treating larvae of the butterfly Colias eurytheme with the eicosanoid biosynthesis inhibitor dexamethasone, strongly impaired nodulation reactions to bacterial infections. The influence of dexamethasone was reversed by treating infected insects with arachidonic acid, an eicosanoid precursor. An eicosanoid biosynthesis system in C. eurytheme larvae is documented. Specifically, the presence of eicosanoid-precursor polyunsaturated fatty acids in tissue phospholipids was determined, an intracellular phospholipase A 2 that can release arachidonic acid from tissue phospholipids was recorded, and eicosanoid biosynthesis, registered as conversion of exogenous radioactive 20:4n–6 into eicosanoids, was observed. These findings support the hypothesis that eicosanoids mediate cellular immune responses to bacterial infections in these butterfly larvae, and more broadly, in most, if not all, insects.

Fatty acid compositions of phospholipids and triacylglycerols of selected tissues, and fatty acid biosynthesis in adult periodical cicadas, Magicicada septendecim

Fatty acid compositions of phospholipids and triacylglycerols prepared from selected body segments (head/thorax and abdomen) and tissues (fat body, alimentary canal, gonads, head and thoracic muscles) of adults of the periodical cicada, Magicicada septendecim, were determined. Adult males and females yielded similar fatty acid profiles. Saturated and unsaturated C16 and C18 fatty acids were the predominant components, which varied slightly among tissues. The eicosanoid-precursor polyunsaturated fatty acid, 20:4 n-6, was present in very low quantities, which varied among tissue sources. Adult periodical cicadas were competent to biosynthesize fatty acids from radioactive acetate. Compared to males, females incorporated just over five times more radioactivity into fatty acids. The radioactive components were incorporated into complex lipids in the fat body and gonads. In the fat body and ovaries, most radioactivity was incorporated into neutral lipid fractions, while in testes most radioactivity was incorporated into phospholipids. These data indicate that even though periodical cicadas have evolved very unusual life history patterns, fatty acid metabolism and composition in adults is similar to patterns seen in many terrestrial insect species.

Eicosanoids mediate nodulation reactions to bacterial infections in adults of the cricket, Gryllus assimilis

Nodulation is the temporally and quantitatively most important cellular defense reaction to bacterial infections in insects. Inhibition of eicosanoid biosynthesis in adults of the cricket, Gryllus assimilis, immediately prior to intrahemocoelic injections of the bacterium, Serratia marcescens, sharply reduced the nodulation response. Separate treatments with specific inhibitors of phospholipase A 2, cyclooxygenase, and lipoxygenase reduced nodulation, supporting our view that nodule formation is a complex process involving lipoxygenase and cyclooxygenase products. The inhibitory influence of dexamethasone was apparent within 2 h of injection, and nodulation was significantly reduced, relative to control crickets, over 22 h. The dexamethasone effects were reversed by treating bacteria-injected insects with the eicosanoid-precursor polyunsaturated fatty acid, arachidonic acid. Low levels of arachidonic acid were detected in fat body phospholipids, and fat body preparations were shown to be competent to biosynthesize eicosanoids from exogenous radioactive arachidonic acid. These findings in a hemimetabolous insect broaden our hypothesis that eicosanoids mediate cellular immune reactions to bacterial infections in most, if not all, insects.

Eicosanoids Mediate Nodulation Responses to Bacterial Infections in Larvae of the Silkmoth, Bombyx mori

1) Nodulation is the first, and qualitatively predominant, cellular defense reaction to bacterial infections in insects and other invertebrates; 2) treating silkworms, Bombyx mori, with the eicosanoid biosynthesis inhibitor, dexamethasone, strongly reduced nodulation responses to bacterial infections; 3) the influence of dexamethasone was reversed by injecting the eicosanoid-precursor polyunsaturated fatty acid, arachidonic acid (20:4n-6), into dexamethasone-treated, infected larvae; 4) the presence of an eicosanoid biosynthesis system in silkworms was documented. Demonstrated elements include a digestive phospholipase A2, incorporation of exogenous 20:4n-6 into fat body phospholipids, the presence of 20:4n-6 in cellular phospholipids, a fat body intracellular phospholipase A2 that can hydrolyze 20:4n-6 from cellular phospolipids, and eicosanoid biosynthetic enzymes; and 5) these findings support the hypothesis that eicosanoids mediate cellular immune responses to bacterial infections in silkworms.

Eicosanoids mediate nodulation responses to bacterial infections in larvae of the tenebrionid beetle, Zophobas atratus

Nodulation is the temporally and quantitatively predominant cellular defense response to bacterial infection in insects and other invertebrates. Inhibition of eicosanoid biosynthesis in larvae of the tenebrionid beetle, Zophobas atratus, immediately prior to intrahemocoelic injections with heat killed preparations of the bacterium, Serratia marcescens, strongly reduced the nodulation response. Separate treatments with specific inhibitors of phospholipase A 2, cyclooxygenase, and lipoxygenase reduced nodulation, supporting the view that nodule formation is a complex process involving both cyclooxygenase and lipoxygenase products. The inhibitory effects of the phospholipase A 2 inhibitor, dexamethasone, on nodulation were apparent 1 h after infection, and the effects increased, relative to controls, over 24 h. The dexamethasone effects were expressed in a dose-dependent manner, and they were reversed by treating bacteria injected insects with the eicosanoid-precursor polyunsaturated fatty acid, arachidonic acid (C20:4n-6). Treatments with the saturated fatty acid, 16:0, which is not an eicosanoid precursor, did not reverse the dexamethasone effects on nodulation. The insects contain low levels of three eicosanoid precursor polyunsaturated fatty acids in six different tissues, and fat body preparations are competent to produce both cyclooxygenase and lipoxygenase products. These findings strongly support the identification of nodulation as a specific insect cellular defense mechanism that is mediated by eicosanoids.

Eicosanoid biosynthesis inhibitors modulate basal fluid secretion rates in the Malpighian tubules of the ant, Formica polyctena

Inhibition of eicosanoid biosynthesis in in vitro preparations of Malpighian tubules isolated from adult ants, Formica polyctena, reduced basal fluid secretion rates. Inhibition of total eicosanoid biosynthesis with 100 μM 5,8,11,14-eicosatetraynoic acid (ETYA) and inhibition of prostaglandin biosynthesis with 100 μM indomethacin strongly reduced basal fluid secretion. The lipoxygenase inhibitor esculetin and the epoxygenase inhibitor SKF-525A did not influence fluid secretion rates during its application, although it blunted the cAMP effect somewhat after washout. These findings indicate that prostaglandins are involved in regulating fluid secretion rates in ant Malpighian tubules. Although stimulation by cAMP was somewhat reduced, the influence of ETYA and indomethacin on fluid secretion rates did not prevent adenosine 3′,5′-cyclic monophosphate from exerting its secretagogue effect. This indicates that the eicosanoid biosynthesis inhibitors acted in a physiological way on the Malpighian tubules. The eicosanoid-precursor polyunsaturated fatty acid, arachidonic acid, is present in phospholipids of Malpighian tubules. This finding indicates that substrate for prostaglandin biosynthesis is available.

Eicosanoids mediate insect nodulation responses to bacterial infections.

We propose that nodule formation is mediated by eicosanoids in insects. Nodulation is the temporally and quantitatively predominant cellular defense response to bacterial infection in insects and other invertebrates. Inhibition of eicosanoid biosynthesis in larvae of the tobacco hornworm Manduca sexta immediately prior to intrahemocoelic infections with the bacterium Serratia marcescens strongly reduced the nodulation response. Inhibition of eicosanoid biosynthesis also reduced formation of cellular aggregates at 1 hr postinfection, which indicates that eicosanoids mediate early stages of nodulation. Separate treatments with specific inhibitors of phospholipase A2, cyclooxygenase, and lipoxygenase reduced nodulation, which supports the view that nodule formation is a complex process involving prostaglandins and lipoxygenase products. The inhibitory effects of the phospholipase A2 inhibitor dexamethasone on nodulation were apparent by 1 hr after infection, and the effects increased, relative to controls, over 24 hr. The dexamethasone effects were expressed in a dose-dependent manner, and they were reversed by treating infected insects with eicosanoid-precursor polyunsaturated fatty acids. Treatments with the saturated fatty acid 16:0, which is not an eicosanoid precursor, did not reverse the dexamethasone effects on nodulation. These findings strongly support the identification of nodulation as a specific insect cellular defense mechanism that is mediated by eicosanoids.

Incorporation of polyunsaturated fatty acids into phospholipids of hemocytes from the tobacco hornworm, Manduca sexta

We examined the incorporation of four radioactive fatty acids, 18:1n-9, 18:2n-6, 20:4n-6 and 20:5n-3, into cellular lipids of hemocytes from tobacco hornworms, Manduca sexta. Most of the radioactivity associated with 18:1n-9 was recovered from triacylglcyerols (TGs), and the radioactivity associated with 18:2n-6 was heavily incorporated into phospholipids (PLs) and TGs. Most of the radioactivity associated with the two eicosanoid-precursor polyunsaturated fatty acids (PUFAs), 20:4n-6 and 20:5n-3, was incorporated into PLs. The incorporated fatty acids were redistributed among the lipid classes during 2 h incubations. The two C20 PUFAs were moved from PLs to TGs. While 18:2n-6 underwent little change, 18:1n-9 was redistributed from TGs to PLs. Within PLs, each of the fatty acids were incorporated into phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylglycerol (PtG) and phosphatidylserine/inositol (PS/PI). The incorporation patterns changed over time, indicating that the incorporated fatty acids were redistributed among the four PL fractions. The radioactivity associated with 18:1n-9 was mostly recovered from the sn-1 position of PC (59%) and PE (83%). Most of the radioactivity associated with 18:2n-6 was found in the sn-2 position of PC (88%) and PE (67%). Over 90% of the radioactivity associated with 20:5n-3 was recovered from the sn-2 position of PC and PE. Incorporation of 20:4n-6 differed from 20:5n-3 because more radioactivity was recovered from the sn-2 position of PC (93%) than PE (69%). These findings are in line with the general background of lipid biochemistry, from which incorporation of 20:4n-6 into PE marks a notable departure: 31% of the radioactivity associated with this acid was recovered from the sn-1 position of PE. These findings indicate that hemocytes from the tobacco hornworm elaborate a fatty acid incorporation system, which exhibits specificity with respect to fatty acid structure and lipid class.

Fatty acid compositions of phospholipids and triacylglycerols from selected terrestrial arthropods

The fatty acid compositions of phospholipids and triacylglycerols from selected orthognath spider tissues, scorpion body segments, whole millipedes, and whole labidognath spiders were determined. The major components were C16 and C18 saturated and unsaturated fatty acids as well as C20 polyunsaturated fatty acids. The eicosanoid precursor polyunsaturated fatty acids 20:4n-6 and 20:5n-3 were present in substantial proportions of phospholipids in all tissues examined. The fatty acid profiles of these terrestrial arthropods differ markedly from corresponding profiles of terrestrial insects in that substantially greater proportions of C20 polyunsaturated fatty acids are present in the organisms in this study. This finding supports the idea that maintaining low proportions of C20 polyunsaturated fatty acids is a special condition of terrestrial insects.

Phospholipid and triacylglycerol fatty acid compositions of five species of Diabrotica (insecta: coleoptera: chrysomelidae)

1. 1. The fatty acid compositions of phospholipids and triacylglycerols from whole adults and larvae of the beetles Diabrotica virgifera virgifera, D. balteata and D. undecimpunctata howardi were determined. Whole adults, but not larvae, of D. longicornis and D. barberi were similarly analyzed. 2. 2. The major fatty acid components included the usual C16 and C18 saturated and monounsaturated fatty acids that are expected from animal tissues. C20 eicosanoid-precursor polyunsaturated fatty acids were present in all species, albeit in very low titres. 3. 3. The fatty acid profiles of phospholipids and triacylglycerols were substantially different. 4. 4. The five insect species differed in fatty acid compositions. 5. 5. Certain polyunsaturated fatty acids that are not found in the host plants of these insects were present in the insect tissue phospholipids. 6. 6. Biosynthesis of certain polyunsaturated from 18:2 n-6 and 18:3 n-3 is inferred from these observations.