Eicosanoid Generation Research Articles

Prefatory Letter

Annals of the New York Academy of SciencesVolume 744, Issue 1 p. xi-xi Prefatory Letter Rodolfo Paoletti, Rodolfo PaolettiSearch for more papers by this author Rodolfo Paoletti, Rodolfo PaolettiSearch for more papers by this author First published: November 1994 https://doi.org/10.1111/j.1749-6632.1994.tb52716.xAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume744, Issue1Cellular Generation, Transport, and Effects of Eicosanoids: Biological Roles and Pharmacological InterventionNovember 1994Pages xi-xi RelatedInformation

Inhibitory activity of a series of coumarins on leukocyte eicosanoid generation.

Sixteen plant-derived or synthetic coumarins with different patterns of substitution were tested for their capacity to modify A23187-induced synthesis of leukotriene B4 and thromboxane B2 via the 5-lipoxygenase and cyclooxygenase pathways of arachidonate metabolism in rat peritoneal exudate leukocytes. Five of the 16 coumarins inhibited LTB4 production: all contain orthodihydroxy substitutions (approximate IC50 values 8-100 microM). The mechanism is likely to depend upon a combination of the coumarins' iron-chelating and iron ion-reducing abilities, properties which also confer beneficial activities of these compounds as scavengers of reactive oxygen species (Payá et al., Biochem. Pharmacol. 44, 205-214 (1992)). Inhibition of the cyclooxygenase pathway was only demonstrated by one compound, 5,7-dihydroxy-4-methylcoumarin, which did not inhibit 5-lipoxygenase, indicating that the cyclooxygenase inhibitory mechanism is different. Similar effects of the active coumarins were obtained using arachidonic acid as substrate for rat leukocyte eicosanoid generation, confirming that they act at the 5-lipoxygenase/cyclooxygenase level. The same profile of activity was also shown when the coumarins were tested against 5-lipoxygenase in human polymorphonuclear neutrophils. Taken together, these antioxidant and anti-eicosanoid properties of coumarins could be exploited for the design of potentially valuable non-toxic anti-inflammatory agents for treating diseases in which eicosanoid generation and the production of reactive oxygen species are involved.

Follicle-Stimulating Hormone-Induced Phospholipase A2 Activity and Eicosanoid Generation in Rat Sertoli Cells1

The possibility that FSH stimulates the phospholipase A2 (PLA2) pathway was studied in cultured immature Sertoli cells. FSH induced [3H]-arachidonic acid (AA) release from prelabeled cells in a time- and concentration-dependent fashion (ED50 = 21.8 +/- 1.9 ng/ml). This response could be fully prevented by pretreatment of cells with the PLA2 inhibitor, mepacrine. That PLA2 was the main enzyme responsible for cleavage of AA from membrane phospholipids was directly shown by PLA2 activity assay using vesicles of radiolabeled phosphatidylcholine (PC) as substrate. Furthermore, FSH stimulated eicosanoid generation in a time-dependent manner through the cyclooxygenase but not the lipoxygenase pathway. In fact, higher levels of prostaglandin (PG) E2, F2 alpha, and the stable products of PGI2 and thromboxane A2 (6-keto PGF1 alpha and thromboxane B2, respectively) were generated by the gonadotropin-treated cells as compared to control cells. The effect was inhibited by mepacrine, further supporting the pivotal role of PLA2 in the release of the eicosanoid precursor, AA. Finally, the effect of the main product of FSH-induced AA metabolism, i.e., PGE2, was studied. Intracellular cAMP accumulation in Sertoli cells was stimulated by the prostanoid in a dose-dependent manner (ED50 = 2.3 +/- 0.37 nM). PGE2 also significantly stimulated aromatase activity, a specific marker of Sertoli cell functions, measured as 17 beta-estradiol production (ED50 = 4.7 +/- 0.8 nM). Similar results were obtained with PGF2 alpha. Our findings show that FSH, through the activation of PLA2, leads to AA release with consequent metabolism by the cyclooxygenase pathway.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence that secretory phospholipase A2 plays a role in arachidonic acid release and eicosanoid biosynthesis by mast cells.

This study investigated the role of secretory PLA2 (sPLA2) in arachidonic acid (AA) release and lipid mediator generation in mouse bone marrow-derived mast cells. Initial studies indicated that mast cells contain multiple PLA2 activities and secreted PLA2 activity upon Ag stimulation. The secreted PLA2 activity is blocked by DTT and by a group II PLA2-neutralizing Ab. Mast cells incubated with groups I or II PLA2 selectively release polyunsaturated fatty acids, such as AA, into supernatant fluids. The bulk of AA released by sPLA2 is derived from phosphatidylethanolamine. The fatty acids released by extracellular PLA2 mimic those found in supernatant fluids after Ag stimulation of mast cells. Incubation of mast cells with PLA2 generates cyclooxygenase (CO) products but no 5-lipoxygenase (5-LO) products. Ag, but not PLA2, induces the translocation of 5-LO to cellular membranes and the formation of 5-LO products. The addition of sPLA2 to Ag-stimulated mast cells increases the synthesis of 5-LO products. Octadeuterated AA (2H8AA) added to the outside of cells to trace extracellular AA metabolism is rapidly converted to CO products. Addition of sPLA2, or Ag in combination with 2H8AA reduces the quantity of 2H8AA converted to deuterated CO products, when compared with adding 2H8AA alone. The reduction of deuterated CO products can be accounted for with increases in nondeuterated CO products. 2H8AA is only converted to 5-LO produces when mast cells are activated with Ag. The amount of 2H8AA converted to deuterated 5-LO products is reduced by the addition of PLA2 to Ag-stimulated cells. The competitive formation of deuterated and nondeuterated products observed when mast cells are incubated with 2H8AA, indicates that extracellular AA released by sPLA2 is used for both CO and 5-LO product formation. Taken together, these data reveal a role for sPLA2 in the release of AA and demonstrate that AA released by this mechanism is used for eicosanoid generation.

Effect of leflunomide on constitutive and inducible pathways of cellular eicosanoid generation

Leflunomide exerts its effects primarily via the immunomodulating and antiphlogistic activities of its major metabolite A 77 1726. Our investigation in several eicosanoid forming systems revealed that in human white blood cells the metabolite did not cause any alteration on Ca-ionophore stimulated metabolism of membrane bound arachidonic acid to cis-, trans- and epi-LTB4. Thus, the involved enzyme systems phospholipase A2, 5-lipoxygenase and LTA4-hydrolase can be ruled out as a target of the drug. However, in several cellular systems the drug weakly inhibited the generation of 5-HETE and LTB4 from exogenous arachidonic acid, possibly by interfering with the exogenous substrate's access to the 5-lipoxygenase. In order to get information about the cyclooxygenase (COX-2) which is inducible in human PMNL by inflammatory mediators via de novo protein biosynthesis, we activated the cells with LPS for 18 h. A 77 1726 and indomethacin had no influence on the enzyme activity of the newly induced COX-2. However, both drugs in low concentrations were able to blunt the long term activation process resulting in PGE2 generation. In contrast, the prostaglandins generated by constitutive enzymes (COX-1) are probably involved in maintaining vital functions, and their inhibition by indomethacin and other nonsteroidal antiinflammatory drugs (NSAIDs) account for numerous adverse effects, for instance gastric erosion. Our study revealed that leflunomide and A 77 1726 are not to be regarded as COX-1-inhibitors, and thus cannot be associated with the typical adverse effects of the NSAIDs.

Nicotine-induced release of elastase and eicosanoids by human neutrophils

We examined the direct effects of nicotine on a variety of neutrophil functions at concentrations achievable in lung and oral tissues from cigarette smoking. The results show dose-dependent suppression of chemotaxis and phagocytosis, and enhancement of degranulation and eicosanoid generation, but not superoxide production. Cell viability was not affected by the concentrations of nicotine used in these experiments, as shown by trypan blue dye exclusion and MTT assays. These results implicate nicotine as the ingredient in cigarette smoke responsible for inflammatory damage to lungs and oral tissues observed in cigarette smokers.

アラキドン酸カスケード作動酵素としてのホスフォリパーゼＡ２

Phospholipase A2 (PLA2) plays a crucial role in diverse cellular responses including phospholipid digestion and metabolism, host defene, and signal transduc-tion. PLA2 provides precursors for eicosanoid generation when the cleaved fatty acid is arachidonate. Mammalian tissues and cells generally contain more than one PLA2 enzyme. Recent advances in molecular and cellular biology enabled us to understand the molecular nature, possible function and regulation of each PLA2 isozymes. Cytosolic PLA2 (cPLA2) and secretory PLA2 (sPLA2) are the most well characterized PLA2s amongst a still expanding large family of mammalian PLA2s. cPLA2 exists in the cytosol of various types of cells almost ubiquitously. It exhibits arachidonate-preference and the activity is regulated by protein phosphorylation. sPLA2 is also widely distributed in mammalin tissues and cells. In particular, sPLA2 in detected extracellularly in inflamed sites of experimental animals and human. Participation of sPLA2 in arachidonate metabolism is also demonstrated. Here, I focus on recent studies of involvement of cPLA2 and sPLA2 in eicosanoid generation.

Ethanol inhibits zymosan-stimulated eicosanoid production in mouse peritoneal macrophages

Resident peritoneal macrophages synthesized and released eicosanoids when challenged by zymosan, a phagocytosable particle. Incubation of these cells with ethanol resulted in dose-dependent inhibition of arachidonic acid release and eicosanoid generation in response to zymosan. Ethanol affected the extent but not the ratio of eicosanoids released. When assayed in a cell-free system, endogenous phospholipase A 2 activity was neither affected by the presence of ethanol in the incubation medium nor by preincubation of the cells with ethanol. Ethanol also inhibited arachidonic acid release in response to phorbol myristate acetate, a compound that, like zymosan, triggered a pertussis-toxin-sensitive response. When cells that had been previously treated with pertussis toxin were used, no further inhibitory effect of ethanol was seen in response to both zymosan and phorbol myristate acetate. On the other hand, ethanol had no effect on arachidonic acid release stimulated by ionophore A23187 or lipopolysaccharide, two compounds that triggered a pertussis-toxin-insensitive response. Moreover, ethanol was able to nearly abolish arachidonic acid release in response to fluoroaluminate, a direct activator of G-proteins. Altogether, the results of this study suggest that ethanol inhibits zymosan-stimulated eicosanoid production by interacting with a G-protein — or a G-protein-mediated process — that is critically involved in arachidonic acid mobilization.

Peroxynitrite-induced rat colitis—A new model of colonic inflammation

Background: Excessive production of nitric oxide, characteristic of inflamed states, may have deleterious effects through its facile conversion (in the presence of O2) to peroxynitrite, which promotes lipid and sulfhydryl oxidation. This study assessed the effect of peroxynitrite on the rat colon. Methods: Peroxynitrite was administered intrarectally to rats. One, 3,7, and 21 days after treatment, a distal colonic segment was isolated and tissue was obtained for histological evaluation and determination of myeloperoxidase activity and NOx, and eicosanoids generation. Results: Within 24 hours, the exposed segment was edematous and congested with occasional hemorrhagic mucosal ulceration. On day 7, the lumen was narrow; at day 21, there were signs of stenosis. Histological analysis showed transmucosal necrosis, acute inflammation, and exudative edema 24 hours after treatment. Surface re-epithelization and infiltration of granulation tissue were present at 1 week. Resolution of edema, mucin repletion, thickening of muscularis mucosa and propria, and fibrosis were observed at 3 weeks. Significant increase in NOx generation and myeloperoxidase and NO synthase activities were observed at 24 hours, whereas enhanced leukotriene generation was observed only at 21 days. Conclusions: Peroxynitrite-induced colonic inflammation provides a novel model of NO-related tissue injury and offers the opportunity to further explore the potential role of NO in the pathogenesis of inflammatory bowel disease.

Short-term regulation of renal Na-K-ATPase activity: physiological relevance and cellular mechanisms

Sodium-potassium-activated adenosinetriphosphatase (Na-K-ATPase; the Na:K pump), located at the basolateral domain of epithelial cells, provides the driving force for active sodium and potassium translocation and for the secondary active transport of other solutes across the renal tubules. Short-term regulation of renal Na-K-ATPase activity (i.e., not reflecting changes in its biosynthesis rate) provides an important mechanism of modulating tubule transport and thus the final Na and K urinary excretion. Recent studies have provided abundant evidence that such regulation is effected by complex functional networks that are specific for different nephron segments and involve distinct and often mutually interacting intracellular signal transduction pathways. The effects of hormones and autacoids linked to alterations in cell adenosine 3',5'-cyclic monophosphate and consequently of protein kinase A, in the levels and distribution of protein kinase C, or in the generation of various eicosanoids provide examples of rapid Na:K pump activity modulation by the mechanisms mentioned above. In this review we assess the roles of specific intracellular messengers and the manner in which they, and especially protein kinases, might interact with the pump in the short-term regulation of its activity; also, we examine the emerging evidence supporting the participation of the cytoskeleton in this process.

Cellular generation, transport and effects of eicosanoids: Biological roles and pharmacological intervention: November 14–17, 1993: The Grand Hotel, Stockholm, Sweden. Chairs: Edward J. Goetzl, University of California, San Francisco; Marek Rola-Pleszczynski, University of Sherbrooke Faculty of Medicine, Canada

Cellular generation, transport and effects of eicosanoids: Biological roles and pharmacological intervention: November 14–17, 1993: The Grand Hotel, Stockholm, Sweden. Chairs: Edward J. Goetzl, University of California, San Francisco; Marek Rola-Pleszczynski, University of Sherbrooke Faculty of Medicine, Canada

Involvement of Phospholipase A 2 Activation and Arachidonic Acid Metabolism in the Cytotoxic Functions of Rat NK Cells

Arachidonic acid (AA) release via phospholipase A 2 (PLA 2) activation and generation of eicosanoids have been implicated as playing signaling roles in a variety of cell types. Here we show evidence that interaction of fresh NK cells with membranes from sensitive or antibody (Ab)-coated targets generates eicosanoids through both cycloxygenase (CO) and lipoxygenase (LO) pathways. Eicosanoid generation is attributable to PLA 2 activation since pretreatment with PLA 2 irreversible inhibitors, such as mepacrine or parabromophenacylbromide (pBPB), completely blocks AA metabolite generation. The involvement of PLA 2 or AA metabolites in the cytotoxic functions of rat NK cells has also been investigated. Treatment of effector cells with mepacrine or pBPB resulted in complete, irreversible, dose-dependent inhibition of both NK and ADCC activities, which were completely reversed by the addition of exogenous PLA 2 or its hydrolysis products, AA and lysophosphatidylcholine (lysoPC). Among the metabolites of AA released by NK cells, the 5-LO product leukotriene B 4 (LTB 4) seems to play an important role in cytolytic activities of NK cells. Indeed, the LO inhibitor, nordihydroguaiaretic acid (NDGA), totally abrogated both NK and ADCC activities, which were restored by the addition of exogenous LTB 4. However, the failure of LTB 4 to reverse mepacrine or pBPB-induced inhibition of NK and ADCC suggests that its effects could be mediated by PLA 2. The results are consistent with a crucial role for the target-stimulated AA release as a fundamental step in the signal transduction pathway in NK cell. Moreover, LTB 4 generation seems to be responsible for further PLA 2 activation in a second step leading to the amplification of response.

Production of eicosanoids in response to endothelin-1 and identification of specific endothelin-1 binding sites in airway epithelial cells.

The effect of endothelin-1 (ET-1) on arachidonate metabolism in the respiratory epithelium was investigated in primary cultures of feline tracheal epithelial cells. Subconfluent epithelial cell cultures were stimulated by ET-1, and eicosanoid generation was determined by high performance liquid chromatography (HLPC) of 3H-labeled arachidonic acid (AA) metabolites and by radioimmunoassay (RIA) of corresponding nonradiolabeled HPLC elution. The HPLC chromatograms of [3H]AA-prelabeled samples revealed that ET-1 (10(-5) M) augmented the release of prostaglandin (PG) E2, 12-hydroxyeicosatetraenoic acid (HETE), PGF2 alpha, and AA. RIA of corresponding nonradiolabeled HPLC elution demonstrated a significantly increased release of PGE2, PGF2 alpha, and 12-HETE as well as 5-HETE in response to ET-1 stimulation. 5-HETE release from ET-1-stimulated cells was further identified by gas chromatography/mass spectrometry (GC/MS). The stimulating effect of ET-1 on AA metabolism was dose dependent (10(-5) to 10(-7) M) and peaked within 1 h with a progressive decline over the subsequent hours. Using 125I-labeled ET-1 as radioligand, the presence of specific binding sites for ET-1 was demonstrated in cultured feline tracheal epithelial cells. ET-1 binding reached equilibrium within 1 h at 37 degrees C. Scatchard analysis suggested the existence of two saturable binding sites, with the estimated equilibrium dissociation constant (Kd) of 35.3 pM and maximal binding capacity (Bmax) of 15.0 fmol/10(7) cells for the higher affinity binding site and Kd of 205.9 pM and Bmax of 35.0 fmol/10(7) cells for the lower affinity binding site.(ABSTRACT TRUNCATED AT 250 WORDS)

Rat and human pancreatic islet cells contain a calcium ion independent phospholipase A2 activity selective for hydrolysis of arachidonate which is stimulated by adenosine triphosphate and is specifically localized to islet .beta.-cells

The recent demonstration that myocardial Ca(2+)-independent phospholipase A2 exists as a complex of catalytic and regulatory polypeptides that is modulated by ATP has suggested a novel mechanisms through which alterations in glycolytic flux can be coupled to the generation of eicosanoids which facilitate insulin secretion. To determine the potential relevance of this mechanism, we examined the kinetic characteristics, substrate specificities, and cellular locus of phospholipase A2 activity in pancreatic islets. Rat pancreatic islets contain a Ca(2+)-independent phospholipase A2 activity which is optimal at physiologic pH, preferentially hydrolyzes phospholipid substrates containing a vinyl ether linkage at the sn-1 position, and prefers arachidonic acid compared to oleic acid in the sn-2 position. Rat islet Ca(2+)-independent phospholipase A2 activity is inhibited by the mechanism-based inhibitor (E)-6-(bromomethylene)-3-(1-naphthalenyl)-2H-tetrahydropyran-2-one and is stimulated by ATP. Purification of beta-cells from dispersed pancreatic islet cells by fluorescence-activated cell sorting demonstrated that beta-cells (but not non-beta-cells) contain Ca(2+)-independent, ATP-stimulated phospholipase A2 activity. Remarkably, clonal RIN-m5f insulinoma cells, which possess a defect in glucose-induced insulin secretion, contain a Ca(2+)-independent phospholipase A2 which is not modulated by alterations in ATP concentration. Collectively, these results and those of an accompanying paper [Ramanadham et al. (1993) Biochemistry (following paper in this issue)] implicate Ca(2+)-independent phospholipase A2 as a putative glucose sensor which can couple alterations in glycolytic metabolism to the generation of biologically active eicosanoids and thereby facilitate glucose-induced insulin secretion.

Ultrastructural localization of prostaglandin endoperoxide synthase (cyclooxygenase) to isolated, purified fractions of guinea pig peritoneal macrophage and line 10 hepatocarcinoma cell lipid bodies.

Subcellular fractions of purified cytoplasmic, nonmembrane-bound lipid bodies were prepared from [3H]-arachidonic acid-labeled guinea pig peritoneal macrophages and line 10 hepatocarcinoma cells. These fractions, which contained [3H]-arachidonyl lipids, were shown to be devoid of contaminating cellular membranes by electron microscopy, and to contain prostaglandin endoperoxide (PGH) synthase by postembedding immunogold electron microscopy. These findings support a proposed role for these lipid-rich organelles in the generation of eicosanoids by oxidative metabolism of arachidonate in the cyclooxygenase pathway of inflammatory and neoplastic cells.

Release of 14-kDa group-II phospholipase A2 from activated mast cells and its possible involvement in the regulation of the degranulation process.

Group II phospholipase A2 was detected in appreciable amounts in rat peritoneal mast cells. The effect of several inhibitors specific to 14-kDa group-II phospholipase A2, including two proteinaceous inhibitors and a product of microorganisms with a low molecular mass, on mast-cell activation was examined. When rat peritoneal mast cells were sensitized with IgE and then challenged with antigen, the specific phospholipase-A2 inhibitors suppressed histamine release in a concentration-dependent manner. By contrast, these inhibitors showed no effect on prostaglandin generation under the same conditions. Histamine release from rat peritoneal mast cells subjected to non-immunochemical stimuli, such as concanavalin A, the Ca2+ ionophore A23187, compound 48/80 and substance P was also suppressed. When rat peritoneal mast cells were treated with 14-kDa-group-II-phospholipase-A2-specific inhibitors, washed and stimulated, histamine release was not affected appreciably. Similar suppressive effects of the inhibitors on histamine release were observed with mouse cultured bone-marrow-derived mast cells. When bone-marrow-derived mast cells were activated, they secreted both a soluble and an ecto-enzyme form of 14-kDa group-II phospholipase A2, although appearance of the enzyme associated with the external surface of cells was observed transiently. An appreciable amount of membrane phospholipids was degraded during activation of mast cells, which was decreased by treatment with 14-kDa-group-II-phospholipase-A2 inhibitor. These observations suggest that degranulation and eicosanoid generation in mast cells are regulated independently by discrete phospholipases A2 and that the 14-kDa group-II phospholipase A2 released from mast cells during activation may play an essential role in the progression of the degranulation process.

Increased oxygen radical and eicosanoid formation in immune-mediated mesangial cell injury

To evaluate whether monocytes/macrophages derived from glomeruli could be a source of increased eicosanoid and free oxygen radical formation in glomerular disease, monocytes/macrophage (M/M) were isolated from nephritic glomeruli and their in vitro generation of eicosanoids and superoxides were measured. Glomerular immune injury was induced by i.v. injection of a rabbit-anti-rat thymocyte antiserum (ATS). Kidneys were removed two, five, and 24 hours, and three and eight days after ATS. Adhesive glomerular macrophages were obtained by isolation of glomeruli, enzymatic digestion and incubation of the single cell suspensions in culture dishes. O2-production was evaluated by superoxide dismutase (SOD)-inhibitable reduction of ferricytochrome C; PGE2 and TxB2 release was assessed by direct RIA. Glomerular macrophage infiltration was maximal 24 hours after intravenous antibody (35.9 +/- 5.1 M/M per glomerulus). In vitro production of superoxide was significantly enhanced (P less than 0.001) five hours after ATS administration (51.6 +/- 4.4 nmol O2/10(6) MM/hr), when compared with M/M from controls (30.4 +/- 2.0 nmol O2/10(6) MM/hr). TxB2 formation of glomerular M/M was increased (P less than 0.001) two hours and five hours after ATS administration (1056 +/- 75 and 1182 +/- 112 pg TxB2/10(6) MM/hr) compared with controls (390 +/- 34 pg TxB2/10(6) MM/hr). PGE2 synthesis, however, was decreased (P less than 0.01) at five hours after ATS (629 +/- 43 pg PGE2/10(6) MM/hr) compared with controls (950 +/- 125 pg PGE2/10(6) MM/hr). Furthermore, there was release of leukotriene B4 (LTB4) in monocytes of nephritic glomeruli five hours after ATS administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of 5-lipoxygenase and cyclo-oxygenase in leukocytes by feverfew: Involvement of sesquiterpene lactones and other components

Leaves or infusions of feverfew, Tanacetum parthenium, have long been used as a folk remedy for fever, arthritis and migraine, and derived products are widely available in U.K. health food shops. Previous reports have suggested interactions with arachidonate metabolism. Crude chloroform extracts of fresh feverfew leaves (rich in sesquiterpene lactones) and of commercially available powdered leaves (lactone-free) produced dose-dependent inhibition of the generation of thromboxane B 2 (TXB 2) and leukotriene B 4 (LTB 4) by ionophore- and chemoattractant-stimulated rat peritoneal leukocytes and human polymorphonuclear leukocytes. Approximate 1050 values were in the range 5–50 μg/mL, and inhibition of TBX 2 and LTB 4 occurred in parallel. Isolated lactones (parthenolide, epoxyartemorin) were also inhibitory, with approximate ic 50 values in the range 1–5 μg/mL, as were crude extracts treated with cysteine (to neutralize reactive α-methylene butyrolactone functions of the sesquiterpenes). Inhibition of eicosanoid generation appeared to be irreversible but not time-dependent. We conclude that feverfew contains a complex mixture of sesquiterpene lactone and non-sesquiterpene lactone inhibitors of eicosanoid synthesis of high potency, and that these biochemical actions may be relevant to the claimed therapeutic actions of the herb.

Porcine pancreatic phospholipase A 2-induced contractions of guinea pig lung pleural strips

The contractile nature of porcine pancreatic phospholipase A 2 (PLA 2) was characterized on paired pleural strips obtained from guinea pig lung. PLA 2 (0.003–10 U/ml) produced concentration-related contractile responses which were sensitive to various drugs. The major component of the PLA 2-induced contractions was derived from products of the cyclooxygenase pathway since a cyclooxygenase inhibitor or the combination of a thromboxane synthetase inhibitor and a thromboxane receptor antagonist produced a 54–65% reduction of the contractile responses. 5-Lipoxygenase products contributed to a smaller component of the PLA 2-induced responses since 5-lipoxygenase inhibitors or the combination of a leukotriene (LT) B 4 receptor antagonist and an LTD 4/LTE 4 receptor antagonist only suppressed the maximal responses 22–32%. PLA 2-induced contractile responses were nearly abolished by altering both sides of the arachidonic acid cascade simultaneously. In contrast, a PAF receptor antagonist, a histamine (H 1) receptor antagonist and an acetylcholine receptor antagonist, failed to significantly reduce PLA 2-induced responses. These results demonstrate that exogenous administration of porcine pancreatic PLA 2 produced concentration-dependent contractions of pleural strips mediated through the generation of eicosanoids.

Essential fatty acid deficiency normalizes function and histology in rat nephrotoxic nephritis.

The central lipid abnormality in essential fatty acid deficiency (EFAD) is the lack of availability of arachidonic acid. To examine the role of total eicosanoid's biosyntheses in the pathology and pathophysiology of glomerulonephritis, EFAD was induced in weanling rats, which were then subjected to antiglomerular basement membrane antibody (NTS)-induced injury in adulthood. Glomerular dynamics (as assessed by micropuncture), quantitative histology, and eicosanoid generation rates were measured at two hours and two weeks post-NTS, and compared to those of standard diet-fed (STD) controls. Two hours post-NTS, and despite the occurrence of proteinuria in both EFAD and STD animals, glomerular dynamics were essentially normal in EFAD rats, whereas STD animals had reduced values for glomerular filtration rate (GFR) and renal plasma flow rate (RPF). At two weeks, severe histologic changes were observed in STD animals including mesangial and stalk hypercellularity, moderate sclerosis, and interstitial nephritis, coupled with heavy proteinuria and reduced GFR and RPF. In dramatic contrast, EFAD rats displayed totally normal glomerular structures and functions. In parallel, glomerular generation rates of prostaglandin E2 and thromboxane A2 were suppressed markedly in EFAD rats. Thus, EFAD confers complete protection against the histopathologic and functional sequelae of immune-initiated injury in the glomerulus. The data suggest that the initial wave of complement-induced neutrophil infiltration (with resultant proteinuria) is not sufficient to perpetuate injury into the more destructive chronic phases. The results provide strong impetus for the design of more specific interventional therapies targeting the various enzymes and products of arachidonic acid metabolism in the attempts to control glomerular inflammation.