The production of 5-HETE and leukotriene B in rat neutrophils from carrageenan pleural exudates

Bothrops lanceolatus (Fer de lance) venom stimulates leukocyte migration into the peritoneal cavity of mice

The ability of Bothrops lanceolatus venom to induce neutrophil migration into the peritoneal cavity of mice was investigated. Intraperitoneal injection of venom caused dose- and time-dependent neutrophil migration, which peaked with 750 ng of venom/cavity 4h after venom injection. The neutrophil migration was significantly reduced by pretreatment with dexamethasone (0.5 mg/kg, s.c.), an indirect inhibitor of phospholipase A(2) (PLA(2)), and AA861 (0.01 mg/kg, s.c.), a 5-lipoxygenase inhibitor, but in contrast, was not modified by pretreatment with indomethacin (2 mg/kg, s.c.), an inhibitor of the cyclooxygenase pathway, meloxicam (5 mg/kg, s.c.), an inhibitor of the cyclooxygenase-2 pathway, or the PAF inhibitor WEB2086 (40 mg/kg, s.c.). Dexamethasone and AA861 also inhibited the neutrophil migration by 60% when administered immediately after venom injection, and the coadministration of these two drugs caused a 75% reduction in migration. BLV-induced neutrophil migration was not due to contamination by endotoxin since polymyxin B-treated venom retained its activity. Heating the venom (97 degrees C, 2 min) reduced the PLA(2) activity by 64% and this was accompanied by a corresponding reduction (68%) in neutrophil migration. These results suggest that arachidonate-derived lipoxygenase metabolites (possibly leukotriene B(4)) are involved in the chemotaxis observed. Macrophages may be an important source of these metabolites since the migratory response to venom was potentiated in mice pretreated with thioglycollate, but reduced when the peritoneal cavity was washed with sterile saline.

Induction of leukotriene production before antigen challenge enhances antibody affinity in genetically selected mice

Mice genetically selected for their incapacity to produce high-affinity antibody to protein antigens in adjuvant (nonmaturing (NM) mice) were treated with indomethacin, an inhibitor of the cyclooxygenase pathway of arachidonic acid metabolism. Pretreatment with indomethacin significantly enhanced the affinity of antibodies produced 21 days after immunization with human serum albumin (HSA). Blockage of the cyclooxygenase pathway in this way was shown to induce the production of leukotrienes via the lipoxygenase pathway. The production of leukotrienes may well be responsible for the enhanced antibody affinity, since blockage of the lipoxygenase pathway in addition to the cyclooxygenase pathway reversed the effect. In an attempt to elucidate the mechanisms involved, IL-1 production and Ia expression by macrophages were examined. Ia expression by peritoneal cells from untreated NM mice was significantly lower than that by their high-affinity-producing counterparts 3 days after immunization. Indomethacin pretreatment raised inducible Ia antigen levels on macrophages of NM mice to those seen on cells from untreated high-affinity mice. Indomethacin treatment alone induced the production of IL-1 by macrophages in NM mice. However, 3 days after immunization and the withdrawal of indomethacin in NM mice, IL-1 production was significantly lower than the response of NM mice given antigen alone, suggestive of the induction of a feedback mechanism. Thus indomethacin pretreatment results in a cascade of events in macrophages which produce a decrease in IL-1 production and an increase in inducible Ia expression 3 days after antigen challenge.

Enhancement of lipopolysaccharide-induced tumor necrosis factor production in mice by carrageenan pretreatment

Tumor necrosis factor (TNF) is a cytokine which mediates endotoxin shock and causes multiple organ damage. It is thought that macrophage (MP) activation is necessary to increase lipopolysaccharide (LPS)-induced TNF production and lethality. Carrageenan (CAR) is sulfated polygalactose which destroys MP; it is used as a MP blocker. We found that CAR pretreatment can increase both endotoxin-induced TNF production and the mortality rate in mice. The ddY mice (7 to 8 weeks old) were injected intraperitoneally with CAR (5-mg dose) and challenged intravenously with LPS 24 h later. Without CAR pretreatment, LPS doses of less than 10 micrograms did not induce TNF in sera. After pretreatment, however, about 3 x 10(3) to 4 x 10(4) U of TNF per ml was produced after LPS injection at doses of 0.1 to 10 micrograms, respectively. TNF production was significantly increased by CAR pretreatment at LPS doses of more than 10 micrograms. CAR pretreatment rendered the mice more sensitive to the lethal effect of LPS; 50% lethal doses of LPS in CAR-pretreated mice and nonpretreated mice were 26.9 and 227 micrograms, respectively. The mortality of the two groups was significantly different at doses of 50, 100, and 200 micrograms of LPS. CAR increased LPS-induced TNF production and mortality within 2 h, much earlier than MP activators, which needed at least 4 days. Our results made clear that TNF production is enhanced not only by a MP activator but also by a MP blocker.

Eicosanoid release and early changes in two acute non specific inflammatory reactions. Major role of prostacyclin and leukotrienes

We have compared the early development (0-4h) of two acute non-specific inflammatory reactions induced by the intrapleural injection of isologous serum or a suspension of CaPP crystals. The intensity of the reactions was assessed in terms of the exudate volume, the number and ratio of pleural cells and different cell functions and secretions. The number of exudative cells elicited by isologous serum was higher than with CaPP but the PMN/Monocytes ratio was the same. The amount of protein in the serum-induced exudate was constant from 1 h to 4 h and was similar in the CaPP-induced pleural exudate at the latter time. The amount of complement increased similarly in the two models. The chemotactic potency of the exudates and cell supernatants following incubation showed similar values in the two models. Eicosanoid levels were higher in CaPP--than in isologous serum-induced exudates. Prostacyclin and peptidoleukotrienes were released in specially large amounts at the very outset of the inflammatory reactions.

The role of leukotriene B4 in neutrophil infiltration in experimentally-induced inflammation of rat tooth pulp

Inflammation was induced in rat dental pulp by applying bacterial lipopolysaccharide (LPS). Extirpated tissue samples from inflamed pulps were incubated in vitro in a Krebs buffer containing Ca2+ ionophore A23187, and leukotriene (LT) B4 released into the medium was determined by radio-immunoassay. Production of LTB4 could be detected three to 24 h after the application of LPS and showed a maximum at 12 h. Histologically, marked infiltration of neutrophils, but not other leukocytes, was characteristically observed in the LPS-applied pulps, and the temporal change in neutrophil infiltration was almost parallel, but somewhat more delayed than LTB4 production. When BW755C, a dual inhibitor of cyclo-oxygenase and lipoxygenase, was given to the animals before the application of LPS, both the production of LTB4 and the number of infiltrated neutrophils were significantly decreased, whereas administration of indomethacin had no effect. These results suggest that LTB4 may be involved in neutrophil infiltration in pulpal inflammation. It was also suggested that a major early source of LTB4 in experimental pulpitis was leukocytes, primary neutrophils, because the synthesis of LTB4 in the inflammed pulp was diminished by depletion of circulating leukocytes with cyclophosphamide prior to the application of LPS.

Lecithins enhance leukotriene production from white cells

36 x 10(7) WBC were isolated from 120 ml heparinized venous blood by 5% dextran T-500 sedimentation. 20 mg egg lecithin and 20 mg dipalmitoyl lecithin were respectively pretreated in 2 ml 0.15 M Tris buffer by vibration and sonication. WBC were incubated with the pretreated lecithins for 20 min. Leukotrienes (LTs) were identified by HPLC and bioassay, and quantified with an RIA Kit. Crude incubation medium of both lecithin groups caused guinea pig ileum contractions which were antagonized with FPL55712. Incubation media were partially purified with Bond elut C18. Purified samples of both lecithin groups showed LTC4 and LTD4 peaks on HPLC. LTC4 production (pg/10(7) WBC, M +/- SD) was 194.5 +/- 61.7 (n = 5) in control group, 348.9 +/- 95.4 (n = 6) in dipalmitoyl lecithin group, 543.8 +/- 105.6 (n = 6) in egg lecithin group and 105.62 +/- 63.2 (n = 6) in AA-861 + dipalmitoyl lecithin group. LTC4 production of both lecithin groups was significantly higher than that of control group (P less than 0.01 in dipalmitoyl lecithin group and P less than 0.001 in egg lecithin group). Both egg lecithin and dipalmitoyl lecithin enhanced LT production from WBC. LT production was suppressed in the presence of AA-861. The mechanism of the enhancement in LT production is unclear, but these lecithins are apparently not substrates because dipalmitoyl lecithin contains no arachidonic acid.

Effect of cyclooxygenase and lipoxygenase inhibitors on delayed neuronal death in the gerbil hippocampus

The purpose of our study was to examine whether cyclooxygenase and lipoxygenase inhibitors ameliorate delayed neuronal death in the hippocampal CA1 sector in Mongolian gerbils after 5 minutes of forebrain ischemia. Gerbils were injected intraperitoneally with cyclooxygenase inhibitors piroxicam and flurbiprofen or with lipoxygenase inhibitors AA-861 and BW-755C. Seven days after ischemic insult, the animals were perfusion-fixed, and the neuronal density in the hippocampal CA1 sector was estimated. The average neuronal density in unoperated normal gerbils was 247 +/- 9/mm (mean +/- SEM). In ischemic gerbils with vehicle administration, the average neuronal densities were 13 +/- 2, 14 +/- 2, 13 +/- 2, and 13 +/- 1 for piroxicam, flurbiprofen, AA-861, and BW-755C, respectively. The average neuronal densities in ischemic gerbils treated with 1.5 and 10 mg/kg piroxicam and 1.5 and 10 mg/kg flurbiprofen were 13 +/- 2, 194 +/- 9, 19 +/- 5, and 143 +/- 12, respectively. In ischemic gerbils treated with 15 and 100 mg/kg AA-861 and 30 mg/kg BW-755C, the average neuronal densities were 12 +/- 1, 13 +/- 1, and 14 +/- 2, respectively. At their higher doses, both piroxicam and flurbiprofen significantly (p less than 0.01) ameliorated delayed neuronal death in the hippocampal CA1 sector. Our results suggest that cyclooxygenase products play an important role in the development of delayed neuronal injury after cerebral ischemia.

Biosynthesis, catabolism, and biological properties of HPETEs, hydroperoxide derivatives of arachidonic acid

The oxygenation of arachidonic acid by lipoxygenases results in the formation of HPETEs (hydroperoxyeicosatetraenoic acids), the first products of the LOX pathway. These compounds are short lived and are catabolised into various families of more stable compounds of which the HETEs, hepoxilins, lipoxins and leukotrienes have been identified so far. The development of new techniques have helped to identify and understand the structures of various HPETEs and only recently the biological effects of HPETEs and their various catabolites are being unraveled. Although lipoxygenases are ubiquitous, not all tissues possess the same spectrum of lipoxygenase enzymes. Hence different HPETEs can be formed in different tissues. Recent studies have revealed that HPETEs or products derived from them possess a diversity of important biological properties including the regulation of electrolyte flux and eicosanoid and corticosterone syntheses, release of histamine, regulation of oocyte maturation and release of various reproductive hormones. HPETEs appear to be involved in some pathological conditions viz, skin psoriasis, Clarkson's disease, nerve injury and spinal cord ischemia. These novel eicosanoids are associated with the release of insulin as well as renin. Recently HPETEs have been suggested to act as second messengers in the Aplysia sensory neurons and its catabolite, hepoxilin, has been demonstrated to have effects on mammalian hippocampal neurons. The purpose of this review is to provide a brief summary of the formation of the HPETEs and the various families of compounds derived from them as well as the various types of biological activities for these products described so far.

Analysis of blood HETE levels by selected ion monitoring with ricinoleic acid as the internal standard

Selected ion monitoring of mass fragments of peaks from capillary gas chromatograms permits a sensitive and selective analysis of positional isomers of hydroxy-eicosanoids (as their methyl ester, trimethylsilyl ether derivatives). Because deuterated analogs of these HETEs are not readily available, stable isotope dilution cannot be easily performed. We have developed a method for the quantitation of HETEs using ricinoleic acid (12-hydroxy-oleic acid) as an internal standard. Ricinoleic acid is monitored at m/z 187, while 5-, 12-, and 15-HETEs (those commonly found in biological systems) are monitored at m/z 255, 295 and 225 respectively. The procedure has proven linear for levels from 0.03 to greater than 3.0 nmol HETE per nmol standard. There is however significant "crossover" among the HETEs, requiring preliminary resolution of the various isomers by reverse phase HPLC in samples containing more than one HETE. Recovery of authentic standards added to various blood samples through the extraction, resolution and analyses averaged over 90%. Using this procedure, mean plasma concentrations were found to be less than 0.1 microM for all HETEs tested, while serum levels were approximately 0.3, 0.8 and 0.1 microM for 5-, 12-, and 15-HETE respectively. Serum formed in the presence of 2mM arachidonic acid plus 25 microM A23187, to maximize HETE production, contained an average of 4, 22 and 1 microM 5-, 12- and 15-HETE respectively. Thus while normal human plasma contains sufficient quantities of the various HETEs to produce some of the biological effects attributed to these metabolites, there is potential for an even greater production when sufficient substrate is available.

Effect of bicuculline-induced status epilepticus on prostaglandins and hydroxyeicosatetraenoic acids in rat brain subcellular fractions

Rat cerebrum, prelabeled in vivo by intraventricular injection of [1-14C]arachidonic acid, was used to assess cyclooxygenase and lipoxygenase reaction products in total homogenates, cytosol, synaptosomes, and microsomes. Effects of bicuculline-induced status epilepticus on arachidonic acid metabolism in synaptosomes and microsomes were also measured. Lipoxygenase activity, resulting in the synthesis of hydroxyeicosatetraenoic acids (HETEs), and cyclooxygenase activity, resulting in the synthesis of prostaglandins (PGs), were measured by reverse-phase and normal-phase HPLC with flow scintillation detection. Endogenous lipoxygenase products in synaptosomes were identified by capillary gas chromatography-mass spectrometry. PGs and HETEs were detected in all subcellular fractions. The synaptosomal fraction showed the highest lipoxygenase activity, with 5-HETE, 12-HETE, and leukotriene B4 as the major products. Following bicuculline-induced status epilepticus, endogenous free arachidonic acid and other fatty acids accumulated in synaptosomes, but not in microsomes. Incorporation of [1-14C]arachidonic acid into synaptosomal and microsomal phospholipids was decreased after bicuculline treatment. Bicuculline-induced status epilepticus resulted in increased synthesis of HETEs in synaptosomes. PG synthesis increased in the microsomal fraction. When [1-14C]arachidonic acid-labeled synaptosomes and microsomes were incubated for 1 h at 37 degrees C the synthesis of eicosanoids, particularly PGD2, was increased significantly in bicuculline-treated rats, as compared with untreated rats. Depolarization (45 mM K+) of synaptosomes induced a loss of [1-14C]arachidonic acid from phosphatidylinositol, and increased the synthesis of PGD2 and HETEs, an effect that was enhanced in bicuculline-treated rats. This study localizes changes in arachidonic acid metabolism and lipoxygenase activity resulting from bicuculline-induced status epilepticus in the brain subcellular fraction enriched in nerve endings.

Carrageenan stimulates reduction of nitroblue tetrazolium by human neutrophils without membrane depolarization, myeloperoxidase secretion, or increased oxygen consumption

Carrageenan, a sulfated polyanionic polysaccharide, is commonly used to induce inflammation in experimental animals, and this model is used to screen for the effectiveness of antiinflammatory drugs. Carrageenan-induced inflammation has been attributed to a variety of autocoids including histamine, bradykinin, complement, superoxide, and prostaglandins. This study examines the effects of carrageenan on human PMN in a serum-free system. Carrageenan was found to stimulate the reduction of NBT by PMNs without stimulating membrane depolarization, oxygen consumption, H2O2 production, or myeloperoxidase secretion. Carrageenan stimulates a heat-labile, NBT-reducing system which is unassociated with the usual stimulus-response coupling seen with other PMN activators such as PMA, FMLP, and zymosan.

Exudative, cellular and humoral reactions to platelet-activating factor (PAF-acether) in the pleural cavity of rats

The reactions to platelet-activating factor (PAF-acether) injected into the pleural cavity of rats were compared with the reactions in animals injected with 0.9% NaCl. PAF-acether induced a maximum exudate after 30-60 min, which then decreased and disappeared after 24 h. The number of pleural leukocytes in the exudate was clearly decreased 30 min after the injection, was slightly increased after 6 h and was unchanged at other times. The estimation of lipid mediators in the pleural exudate obtained 30 and 60 min after the injection of PAF-acether revealed an increase in type-C4 leukotriene (LTC4) and a decrease in thromboxane B2 (TxB2) and in 6-keto prostaglandin F1 alpha (6-keto PGF1 alpha). In addition, the amount of histamine was found to be lower after 30 min. These results confirm in vivo that some biological effects of PAF-acether seem to involve the participation of other mediators.

Ketoconazole inhibits the biosynthesis of leukotrienes in vitro and in vivo

Ketoconazole inhibits in vitro (IC50:2.6 X 10(-5) M) the formation of 5-HETE and LTB4 by isolated, carrageenin-elicited rat peritoneal PMN leukocytes, challenged with the Ca2+-ionophore A23187 in the presence of [14C]-arachidonic acid ([14C]-AA). The relative potency of various compounds tested in this respect is NDGA greater than nafazatrom greater than phenidone greater than ketoconazole greater than BW 755C. In contrast to the other compounds studies, ketoconazole in vitro, up to 1 X 10(-4) M, has no effect on the fatty acid cyclo-oxygenase or the 12-lipoxygenase-mediated metabolism of [14C]-AA by isolated human platelets; however, it stimulates the 15-lipoxygenase activity in phenylhydrazine-induced rabbit reticulocytes. After oral administration (10-40 mg/kg, -2 hr), ketoconazole inhibits in a dose-dependent way, the leukotriene-mediated anaphylactic bronchoconstriction in guinea pigs. This study demonstrates that ketoconazole is a comparatively specific and orally active inhibitor of the 5-lipoxygenase activity bearing on the production of leukotrienes derived from arachidonic acid.

Update on ibuprofen: review article

Non-steroidal anti-inflammatory drugs (NSAIDs) have become the principal mode of therapy for rheumatic diseases and their use has continued to increase despite concern expressed recently regarding potential hazards (Figure 1). Prior to 1969, a limited number of NSAID drugs were available. Aspirin and indomethacin became the mainstay of treatment but tolerability, particularly gastric irritation, at doses necessary to control rheumatic symptoms limited the usefulness of these valuable agents. The pyrazolone, phenylbutazone, showed slightly better gastro-intestinal (GIT) tolerability but has since been associated with an increased risk of blood dyscrasiae and is now only available for restricted use in most countries. Ibuprofen was the first of a new breed of NSAIDs originally introduced into the United Kingdom in 1969. Chemically quite distinct from its forerunners it was the first of the propionic acid derivatives to be used in rheumatic practice. The propionics have since become the largest, single and most important group of NSAIDs accounting for 50% of NSAID prescriptions in the United Kingdom. It is estimated that over 100 million patients worldwide have received ibuprofen which is now available in over 100 countries throughout the world including all the major markets. Ibuprofen was developed directly as a result of the problems associated with the use of corticosteroids in the treatment of rheumatoid arthritis and also because of the gastro-intestinal irritation and general intolerability of the established NSAIDs, at that time. Ibuprofen was readily accepted because, unlike the previous drugs, its therapeutic efficacy was easily seen to outweigh the severity of its side-effects. Ibuprofen was the first new drug with the potency of aspirin but without its major disadvantages.

5-lipoxygenase from rat PMN lysate

The products of arachidonic acid metabolism in the 15,000xg supernatant of sonicated rat PMN are described. Only products derived from 5-lipoxygenase are observed. These products are 5-HETE and products derived from hydrolysis of LTA4, particularly LTB4. Some minor products derived from decomposition of 5-HPETE are also observed. The dependence of the activity of 5-lipoxygenase on enzyme and on substrate concentrations is presented and discussed in terms of a kinetic model that includes enzyme inactivation during turnover and substrate inhibition. The 5-lipoxygenase activity is stimulated by Ca++ and ATP.

The effect of an aqueous extract of Tanacetum parthenium L. on arachidonic acid metabolism by rat peritoneal leucocytes

The effect of feverfew (Tanacetum parthenium L., Schultz Bip.) as a whole plant on an aqueous extract equivalent to 20 mg dried plant per ml, has been examined on both cyclo-oxygenase and lipoxygenase activity in rat leucocytes in-vitro. At 10-25 micrograms ml-1 feverfew had no effect on the formation of arachidonate metabolites while at highest concentrations (50-200 micrograms ml-1) it inhibited both cyclo-oxygenase and lipoxygenase metabolic products.

Intravenous SRS-induced increases in tracheal mucous gel layer thickness: evidence for thromboxane involvement

Intravenous (IV) slow reacting substance (SRS) challenge produces bronchoconstriction that can be reduced by cyclooxygenase inhibitors. This report shows that IV SRS challenge also produces significant increases in tracheal mucous gel thickness and that the increases are inhibited by pretreatment with indomethacin (4 mg/kg, PO) or imidazole (10 mg/kg, IV). The increase in gel thickness is preceded by increases in plasma thromboxane B2 (TXB2) levels and the inhibition of gel thickening by imidazole is paralleled by decreases in plasma TXB2 levels. Aerosolized SRS produces increases in tracheal mucous gel thickness which are not inhibited by either indomethacin or imidazole, but are significantly inhibited by FPL-55712. These findings indicate that SRS acts, not only directly to stimulate mucous secretion but also indirectly through an indomethacin and imidazole sensitive mechanism.

Arachidonate metabolic pathways in cells harvested from rat pleural cavity at various times after carrageenan administration

Cells were harvested from rat pleural cavity before and during the inflammatory response stimulated by carrageenan injection. The conversion of [14C]arachidonate by intact cells into products of the cyclooxygenase and 5-lipoxygenase pathways was studied in the absence and presence of ionophore. Incorporation of arachidonate into phosphatidic acid was also followed. In the absence of ionophore, the principal arachidonate metabolites of resident macrophages were the cyclooxygenase products, prostacyclin and thromboxane, while mobilized monocytes produced thromboxane as a major product, but very little prostacyclin. Arachidonate-metabolizing enzymes in mobilized monocytes were, in general, less active than those of resident macophages. Cells harvested at times when mobilized neutrophils were the predominant cell type were capable of converting arachidonate into thromboxane and prostaglandins, but not prostacyclin. These cells exhibited the most active turnover of arachidonate into phosphatidic acid, and the extent of this turnover appeared to be temporally related to the presence of edema in the pleural cavity at the time of cell harvest. Enzymatic formation of 5-lipoxygenase products was dependent on calcium and was markedly stimulated by ionophore A23187 in both resident and mobilized pleural cells. Among several non-steroidal drugs tested, cyclooxygenase inhibitors were the most effective in preventing the inflammatory response in the carrageenan model of inflammation.

Inhibition of polymorphonuclear leukocyte 5-lipoxygenase and platelet cyclooxygenase by alpha-(3,5-di-tert-butyl-4-hydroxybenzylidene)-gamma-butyrolacto ne (KME-4), a new anti-inflammatory drug

The effect of alpha-(3,5-di-tert-butyl-4-hydroxybenzylidene)-gamma-butyrolactone (KME-4), a new anti-inflammatory compound, on arachidonate lipoxygenase and cyclooxygenase was investigated. KME-4 showed a dose-dependent inhibition of 5-lipoxygenase activity in both the cytosol (IC50: 0.85 microM) and ionophore A23187-stimulated cells (IC50: 11.5 microM) of guinea pig peritoneal polymorphonuclear leukocytes. KME-4 was also found to inhibit rabbit platelet cyclooxygenase (IC50: 0.44 microM), but had no inhibitory effect on platelet 12-lipoxygenase at concentrations up to 100 microM, whereas BW755C inhibited both enzymes in the same range of concentrations. The results indicate that KME-4 is a dual 5-lipoxygenase and cyclooxygenase inhibitor which is different from BW755C in affecting 12-lipoxygenase. These effects may provide information for understanding the pharmacological activity of KME-4.

Functional role of thromboxane production by acutely rejecting renal allografts in rats

We investigated the role of thromboxane in mediating the reduction in renal function and renal blood flow characteristic of acute renal allograft rejection. We transplanted kidneys from Lewis rats to Brown-Norway recipients. By the third day after transplantation, histologic changes that were consistent with cellular rejection occurred in the kidney. These changes were associated with a moderate reduction in renal function. By day 6, histologic changes of rejection were advanced and included interstitial and perivascular infiltration by mononuclear cells. The clearances of inulin and para-aminohippuric acid were also markedly reduced. As renal function deteriorated, thromboxane B2 (TXB2) production by ex vivo perfused renal allografts increased progressively from 2 to 6 d after transplantation. However, prostaglandin (PG) E2 and 6-keto PGF1 alpha production remained essentially unchanged. There was a significant inverse correlation between the in vivo clearance of inulin and the log of ex vivo TXB2 production. Infusion of the thromboxane synthetase inhibitor UK-37248-01 into the renal artery of 3-d allografts significantly decreased urinary TXB2 excretion and significantly increased renal blood flow (RBF) and glomerular filtration rate (GFR). Although renal function improved significantly after the acute administration of UK-37248-01, GFR and RBF did not exceed 33 and 58% of native control values, respectively. In other animals, daily treatment with cyclophosphamide improved the clearances of inulin and para-aminohippuric acid and reduced thromboxane production by 6-d renal allografts. These studies demonstrate that histologic evidence of rejection is associated with increased renal thromboxane production. Inhibition of thromboxane synthetase improves renal function in 3-d allografts. Cytotoxic therapy improves renal function, reduces mononuclear cell infiltration, and decreases allograft thromboxane production. Thus, the potent vasoconstrictor thromboxane A2 may play a role in the impairment of renal function and renal blood flow during acute allograft rejection.

Ex vivo effects of nonsteroidal antiinflammatory drugs on arachidonic acid metabolism in neutrophils from a reverse passive Arthus reaction

Rat neutrophils isolated from 4-h reverse passive Arthus reaction (RPAR) pleural exudates actively metabolize arachidonic acid via cyclooxygenase and lipoxygenase. Utilizing this system, the effect of oral doses of nonsteroidal antiinflammatory drugs on the ability of these cells to produce HHT, 5-HETE, and LTB from exogenously added arachidonic acid has been investigated. In vitro and ex vivo, indomethacin and timegadine inhibit cyclooxygenase activity in rat pleural neutrophils. In vitro, timegadine is a lipoxygenase as well as a cyclooxygenase inhibitor. This dual inhibition is confirmed by the observation that ex vivo timegadine inhibits the production of lipoxygenase as well as cyclooxygenase metabolites. While indomethacin, a cyclooxygenase inhibitor, primarily inhibits edema formation, the inhibition of both pathways of arachidonic acid metabolism by timegadine is reflected in the drug's ability to reduce cellular influx as well as edema formation in the RPAR pleural cavity inflammatory reaction.

The effect of BW775C on respiratory distress in the rat induced by arachidonic acid

BW775C, an inhibitor of the lipoxygenase and cyclo-oxygenase pathways, inhibits the respiratory distress induced by arachidonic acid in rats. The degree of respiratory distress was measured in terms of respiratory rate using electrodes implanted at each side of the thorax. Indomethacin, an inhibitor of the cyclooxygenase pathway, failed to influence the respiratory distress induced by arachidonic acid. The results implicate the lipoxygenase pathway, i.e. the leukotrienes synthesis inhibition, in the respiratory distress induced by arachidonic acid.

Phthalic acid esters inhibit arachidonate metabolism by rat peritoneal leucocytes

Phthalic acid esters concentration-dependently inhibited the formation of both cyclo-oxygenase and lipoxygenase arachidonate products by rat peritoneal leucocytes. Phthalates are extracted by human transfusion blood stored in pvc bags, and might similarly affect the blood cells when administered to patients.

Effect of K+ depolarization on the synthesis of prostaglandins and hydroxyeicosatetra(5,8,11,14)enoic acids (HETE) in the rat retina. Evidence for esterification of 12-HETE in lipids

[14C]Arachidonic acid is metabolized to prostaglandins and hydroxyeicosatetraenoic acids in the rat retina. After intravitreal injection of [14C]arachidonic acid, 25% of the injected radiolabel was recovered in the retinal lipids. Phosphatidylcholine and phosphatidylinositol were most actively labeled; however, all glycerolipids incorporated arachidonic acid. The synthesis of prostaglandins E2, F2 alpha, D2, 6-keto-F1 alpha, thromboxane B2 and hydroxyeicosatetraenoic acids was measured by high-performance liquid chromatography. The identity of 12-HETE was confirmed by gas chromatography-mass spectrometry. Incubation of prelabeled retinas in vitro promoted the release of [14C]arachidonic acid from glycerolipids. A 12-fold increase in the synthesis of hydroxyeicosatetraenoic acids occurred with no change in the synthesis of prostaglandins. Incubation in a depolarizing medium (45 mM K+) resulted in a selective increase in hydroxyeicosatetraenoic acids, an effect that was blocked by nordihydroguaiaretic acid (1 microM) and eicosatetraynoic acid (10 microM). 12-[3H8]Hydroxyeicosatetraenoic acid, intravitreally injected, was incorporated into retinal lipids with a distribution similar to arachidonic acid. When retinas labeled with 12-[3H8]hydroxyeicosatetraenoic acid were incubated, there was a large release of the incorporated radioactivity, and metabolism to other products with the chromatographic properties of dihydroxyeicosatetraenoic acids. The release of 12-hydroxyeicosatetraenoic acid was not affected by depolarizing conditions (45 mM K+); however, the conversion of 12-hydroxyeicosatetraenoic acid to dihydroxy isomers was stimulated by K+. These experiments demonstrate active pathways for the generation of eicosanoids in the rat retina that are sensitive to membrane depolarization and lipoxygenase inhibitors.

The effect of aspirin on the metabolism of exogenous arachidonic acid in human polymorphonuclear leukocytes

When human polymorphonuclear leukocytes (PMNL) were incubated with exogenous 14C-arachidonic acid (14C-AA), both lipoxygenase and cyclo-oxygenase metabolites were detected. The amount of the 5-lipoxygenase metabolites formed, including 5-hydroxy-6,8,11,14-eicosatetraenoic acid (5-HETE), was small. The amount of other mono-HETE's (migrating in the vicinity of 12-HETE) was greater, but this was obviously mainly due to the small amount of contaminating platelets. In the presence of calcium ionophore A23187 the rate of formation of 5-HETE was increased, but the formation of other metabolites remained unchanged. When PMNL were incubated with aspirin in the presence of A23187 the formation of the cyclo-oxygenase products was decreased but that of 5-HETE was unchanged. The present study indicates that the calcium ionophore A23187 stimulates specifically the 5-lipoxygenase in human PMNL and that aspirin has no effect on the formation of the 5-lipoxygenase metabolites of arachidonic acid in human PMNL.

Metabolism of arachidonic acid by human neutrophils. Characterization of the enzymatic reactions that lead to the synthesis of leukotriene B4

Human neutrophils stimulated with calcium ionophore A23187 synthesized 5-hydroxyeicosatetraenoic acid (5-HETE) and leukotriene B4. Time-course studies showed that the concentrations of both products reached a maximum after 2 min after which the products were rapidly removed. In longer incubations, 5-HETE was esterified into membrane lipids, and leukotriene B4 was converted to 20- hydroxyleukotriene B4 and/or 20- carboxyleukotriene B4. The reaction is apparently self-limiting. After the maximum was reached, addition of fresh ionophore, Ca2+ or oxygen had little effect. Fresh arachidonic acid increases the yields of 5-HETE and delta 6-trans-leukotriene B4 but not additional leukotriene B4. Only the addition of fresh neutrophils gave additional leukotriene B4. This finding suggests that leukotriene B4 synthesis is limited by both substrate availability and enzyme inhibition by hydroperoxide intermediate. Exogenous arachidonic acid added with ionophore had different effects on the syntheses of leukotriene B4, delta 6-trans-leukotriene B4, and 5-HETE. As the arachidonic acid concentration increases, product formation increases in the following order: 5-HETE greater than delta 6-trans-leukotriene B4 greater than leukotriene B4. At a high concentration (more than 10 microM) of arachidonic acid, the synthesis of delta 6-trans-leukotriene B4 was greater than leukotriene B4 itself. Since delta 6-trans-leukotriene B4 represents the nonenzymatic decomposition of leukotriene A4, we suggest that one of the rate-limiting steps in the synthesis of leukotriene B4 is the leukotriene A4 hydrolase. Our data suggest the synthesis of leukotriene B4 is under the control of three factors: (1) substrate availability; (2) limited capacity of the leukotriene A4 hydrolase, and (3) enzyme inactivators generated during the reaction, such as hydroperoxide intermediate. The tightly controlled system assures only a finite amount of this powerful bioactive substance will be produced under most conditions.

Reduction by dexamethasone of chemotactic activity in inflammatory exudates

Using an experimental model for allergic inflammation of the air pouch type in rats, the effects of dexamethasone and indomethacin on leukocyte infiltration and level of chemotactic activity in the inflammatory exudate were examined to clarify the mechanisms of anti-inflammatory effects of glucocorticoids. Both dexamethasone and indomethacin when locally administered inhibited leukocyte infiltration, while chemotactic activity of the exudate was reduced by dexamethasone only. Indomethacin failed to reduce the level of chemotactic activity. Suppression by dexamethasone of the level of chemotactic activity became evident prior to the decrease in the number of leukocytes in the inflammatory exudate. These results suggest that the anti-inflammatory steroids manifest their inhibitory effect on leukocyte infiltration by inhibiting the generation of chemotactic factors in the inflammatory site. Besides this, the possible production of some inhibitory factors by the steroids may be considered as an alternative mechanism.

Stimulation of prostaglandin synthesis in cultured rat synovial cells by a factor derived from polymorphonuclear leukocytes

Stimulation of synovial cell prostaglandin production by a factor obtained from casein-induced peritoneal polymorphonuclear (PMN) cells has been investigated. Both the extract and short time cultured medium of rat peritoneal PMN cells stimulate prostaglandin (PG)E2 production as well as collagenase production in the culture of rat synovial cells. PGE2 production by the cells in the presence of the PMN factor is much faster (5 to 24 hr) than collagenase production (24 hr or later, Biomedical Res. 3, 506-516, 1982). This stimulating factor is confirmed to be derived from PMN cells, based on the purification of the cells from peritoneal exudate cells by the Ficoll-Urographin method. Elution profile of the factor on gel filtration has indicated that both PGE2 and collagenase productions by synovial cells are stimulated by the same effluent fractions corresponding to molecular weights of 15,000 - 20,000 daltons and 30,000 - 40,000 daltons. These results suggest that PMN cells are involved in PG production as well as collagenase production in the inflamed tissue by stimulating connective tissue cells such as synovial cells.

Prostacyclin and thromboxanes in carrageenan-induced pleurisy in the rat

The cellular origin and kinetics of TXB2 and 6-keto PGF1 alpha in carrageenan-induced pleurisy has been studied. Maximum levels of these prostanoids occurred 1 hour after induction of pleurisy. Mononuclear cells initially present in the pleural cavity synthesized TXB2 and 6-keto PGF1 alpha from (14C) arachidonic acid. By contrast, PMN cells harvested 6 hours after the induction of inflammation did not produce 6-keto-PGF1 alpha. Selective inhibition of thromboxane synthetase with drugs in vitro and in vivo increased the formation of 6-keto-PGF1 alpha, the stable breakdown product of PGI2. This metabolic effect was parallel to an increase in the volume of exudate and in PMN migration. These results suggest that TXA2 seems to be implicated not only as a chemotactic agent but also as an antagonist of PGI2 vasodilator effects.

Pharmacological profile of AA-861, a 5-lipoxygenase inhibitor

AA-861, a selective 5-lipoxygenase inhibitor, suppressed A23187-induced formations of 5-HETE and LTB4 in rat peritoneal macrophages. Immunologically-stimulated generation of SRS-A was also inhibited in guinea pig lung and rat peritoneal cavity. AA-861 had no effects on histamine release from rat mast cells or passive cutaneous anaphylaxis in rats. Essentially no antagonistic activity to LTD4 or histamine was observed. This compound exerted an obvious inhibition of allergic bronchoconstriction in guinea pigs and a moderate reduction of carrageenin-induced paw edema and pleurisy in rats. These findings suggest that SRS-A plays an important role in asthmatic and inflammatory reactions.

Effects of protein deficiency on the metabolism of arachidonic acid by rat pleural polymorphonuclear leukocytes

The effects of protein deficiency on the biosynthesis of metabolites of arachidonic acid by rat pleural polymorphonuclear leukocytes stimulated with calcium ionophore were investigated. The major products of metabolism by lipoxygenase in these cells were leukotriene B4 and 5-hydroxy-6,8,11,14-eicosatetraenoic acid, whereas the major cyclooxygenase products were thromboxane B2 and 12-hydroxy-5,8,10-heptadecatrienoic acid. At high substrate concentrations (100 microM), the formation of all products by polymorphonuclear leukocytes was lower for protein-deficient rats than for controls. Similar results were obtained when products synthesized from endogenous substrate were measured, except that there was no change in the amount of 5-hydroxy-6,8,11,14-eicosatetraenoic acid formed. The biosynthesis of prostaglandins E2 and F2 alpha by homogenates of rat kidney medulla was reduced as a result of protein deficiency. Acetylsalicylic acid inhibited the formation of cyclooxygenase products and stimulated the formation of lipoxygenase products by polymorphonuclear leukocytes. Protein deficiency did not alter the effects of acetylsalicylic acid on the biosynthesis of these products, although at any given concentration the amounts of products formed were less with protein-deficient rats than with rats fed control diets.

Leukotrienes: mediators of immediate hypersensitivity reactions and inflammation

Arachidonic acid plays a central role in a biological control system where such oxygenated derivatives as prostaglandins, thromboxanes, and leukotrienes are mediators. The leukotrienes are formed by transformation of arachidonic acid into an unstable epoxide intermediate, leukotriene A4, which can be converted enzymatically by hydration to leukotriene B4, and by addition of glutathione to leukotriene C4. This last compound is metabolized to leukotrienes D4 and E4 by successive elimination of a gamma-glutamyl residue and glycine. Slow-reacting substance of anaphylaxis consists of leukotrienes C4, D4, and E4. The cysteinyl-containing leukotrienes are potent bronchoconstrictors, increase vascular permeability in postcapillary venules, and stimulate mucus secretion. Leukotriene B4 causes adhesion and chemotactic movement of leukocytes and stimulates aggregation, enzyme release, and generation of superoxide in neutrophils. Leukotrienes C4, D4, and E4, which are released from the lung tissue of asthmatic subjects exposed to specific allergens, seem to play a pathophysiological role in immediate hypersensitivity reactions. These leukotrienes, as well as leukotriene B4, have pro-inflammatory effects.

Differential effects of anti-inflammatory drugs on lipoxygenase and cyclo-oxygenase activities of neutrophils from a reverse passive Arthus reaction

Rat neutrophils isolated from four-hour reverse passive Arthus reaction pleural exudates actively metabolize arachidonic acid. Production of 11-hydroxy- and 15-hydroxy-icosatetraenoic acid and 12-hydroxy-heptadecatrienoic acid is inhibited by indomethacin, benoxaprofen, BW 755C, piroxicam, ibuprofen, timegadine, and naproxen, suggesting that production of these arachidonic acid metabolites occurs at similar enzymic active sites. In addition, in the presence of the calcium inophore A23187 or the non-ionic detergent, BRIJ 56, rat neutrophils also produce the lipoxygenase products 5-hydroxy-icosatetraenoic acid and leukotriene B. The production of these metabolites is calcium dependent. Moreover, the calcium ionophore A23187 and BRIJ 56 synergistically act to augment the metabolism of exogenously added arachidonic acid via lipoxygenase. The formation of these metabolites is inhibited by BW 755C, benoxaprofen and timegadine but not by other non-steroidal anti-inflammatory drugs tested. In fact, at doses which inhibit cyclo-oxygenase activity, indomethacin, naproxen, and ibuprofen stimulate arachidonic acid metabolism via lipoxygenase.

A rapid method for detecting inhibitors of both cyclo-oxygenase lipoxygenase metabolites of arachidonic acid

A method for detecting inhibitors of arachidonic acid metabolism is described. Guinea pig peritoneal polymorphonuclear leukocytes incubated with [14C] arachidonic acid were stimulated with calcium ionophore A23187. The radiolabelled products were identified by HPLC and GC/MS as cyclo-oxygenase and lipoxygenase metabolites. A TLC system was utilized to separate these metabolites which were then analysed by automatic quantitative scanning. This method allowed rapid determination of the radiolabel incorporated into each metabolite. This method of analysis was used to study the actions of indomethacin, NDGA, benoxaprofen, and BW775C on the formation of radiolabelled arachidonic acid metabolites.

A role for the lipoxygenase pathway of arachidonic acid metabolism in glucose- and glucagon-induced insulin secretion

Although the cyclo-oxygenase pathway of arachidonic acid (AA) metabolism inhibits glucose-stimulated insulin release through synthesis of prostaglandins, very little attention has been given to the effects of lipoxygenase pathway products on beta cell function. We have examined the effects of two structurally-dissimilar lipoxygenase inhibitors on insulin release from monolayer-cultured rat islet cells. Both nordihydroguaiaretic acid (NDGA, 20-50 microM) and BW755c (100-250 microM) caused a dose-responsive inhibition of glucose-induced insulin release. This inhibitory effect occurred despite concomitant inhibition of prostaglandin E synthesis. Lipoxygenase inhibitors also impeded cyclic AMP accumulation. Insulin and cyclic AMP release induced by glucagon were also blunted. These studies suggest the hypothesis that AA released in or near the beta cell is metabolized to lipoxygenase product(s) which have feed-forward properties important to glucose- and glucagon-stimulated cyclic nucleotide accumulation and insulin release.

On the biological role of lipid chemotactic factors

Our experimental data of the past seven years cover the generation of a non-preformed lipid-mediator which primarily assayed with guinea pig eosinophils proved to be eosinophil chemotactic. The analysis of the various stimuli led in 1978 to the concept of the phospholipase-arachidonic sequence as a common link for membrane activation. Immunopharmacological studies using either arachidonic acid as stimulus or arachidonic acid analogues provided an early evidence that the lipid chemotactic factor was a lipoxygenase product. These results were supported by analytical studies using thin layer chromatography, reversed phase HPLC, mass spectrometry, the comparison of the lipid chemotactic factor with endogeneous HETEs and by the synthesis of mono- and di-HETEs. It became also evident that mono- and di-HETE are not only mediators but also modulators of inflammatory reactions as was demonstrated for the C5a induced eosinophil chemotactic response. A less pronounced effect on the C5a induced eosinophil and neutrophil chemotactic response was exerted by PAF and its structural analogues. It is also demonstrated that isolated bacterial exotoxins trigger the cells via the phospholipase-arachidonic acid sequence thus generating mono- and di-HETEs leading to the amplification of an inflammatory response.