High-pressure liquid chromatography of oxo-eicosanoids derived from arachidonic acid

Eicosanoids are a large group of biologically active metabolites of arachidonic acid and related C20 fatty acids. Many of these compounds contain hydroxyl groups which can be converted to oxo groups by a variety of substrate-specific dehydrogenases. In many cases, this results in a reduction in potency, but in others, such as the oxidation of 5-hydroxyeicosatetraenoic acid to its oxo metabolite 5-oxo-eicosatetraenoic acid, there is a dramatic increase in biological activity. Thus, it is often very important to analyze the relative amounts of oxo- and hydroxy-eicosanoids formed by various cells and tissues. The present study was designed to compare the chromatographic behavior of oxo-eicosanoids and their hydroxy counterparts in commonly used mobile phases for reversed-phase and normal-phase HPLC. We examined three groups of eicosanoids: prostaglandins, leukotriene B4 and some of its metabolites, and monohydroxy-eicosanoids and their oxo metabolites. We found that in reversed-phase HPLC, the retention times of oxo-eicosanoids were longer than those of the corresponding hydroxy-eicosanoids in mobile phases containing acetonitrile as the major organic component, whereas the reverse was true for mobile phases containing methanol. Normal-phase HPLC using mobile phases containing hexane, isopropanol, and acetic acid gave excellent separation of oxo- and hydroxy-eicosanoids. Increasing the concentration of acetic acid in the mobile phase selectively reduced the retention times of oxo-eicosatetraenoic acids compared to monohydroxy-eicosatetraenoic acids, whereas the reverse was true for isopropanol. Differences in the chromatographic behavior of oxo- and hydroxy-eicosanoids can be useful clues in the structural characterization of these compounds, as illustrated by the chromatographic properties of a complex series of LTB4 metabolites formed by rat neutrophils.

Metabolism of leukotriene B4 in cultured hepatoma cells

Incubation of leukotriene B4 (LTB4) with Hep G2 cells (a human-derived hepatoma cell line) resulted in the production of several metabolites indicative of alternative pathways of LTB4 metabolism not previously observed in normal hepatocytes. The major extracellular LTB4-derived metabolites were structurally identified using mass spectrometry and ancillary techniques including electrospray ionization. The major metabolite was 10-hydroxy-4,6,8,12-octadecatetraenoic acid (10-HOTE), an unexpected metabolite which lost the hydroxy group at carbon 5 from the parent LTB4. Two other major metabolites were 3(R)-hydroxy-LTB4 and 3(S)-hydroxy-LTB4. The formation of these three metabolites revealed that beta-oxidation from the carboxyl terminus can be a significant metabolic pathway for degradation of this hydroxy unsaturated fatty acid. The normal hepatocyte LTB4-derived metabolite, 20-carboxy-LTB4, was observed as only a minor product. The metabolic profile for Hep G2 cells suggests that the efficient cytochrome P-450 pathway involved in omega-oxidation in typical hepatocytes is absent in these cells. Several minor metabolites were also identified which included dihydro products resulting from metabolism by a 12-hydroxydehydrogenase/delta 10-reductase pathway. The formation of the major metabolite reveals the operation of steps in beta-oxidation of hydroxy, unsaturated fatty acids not anticipated by previously identified steps of fatty acid beta-oxidation.

Leukotriene B4 and C4 generation by small intestinal mucosa in children with coeliac disease

The capacity of the small intestinal mucosa to generate leukotriene B4 (LTB4) and C4 (LTC4) in children with coeliac disease (CD) was investigated by measuring the production of LTB4 and LTC4 in intestinal biopsy specimens after stimulation with 10 microM calcium ionophore A23187. In addition, we examined the relationship between the production of LTB4 and LTC4 in the small intestinal mucosa and symptoms of diarrhoea. LTB4 and LTC4 production was significantly higher in biopsies from patients with active CD than from controls (p < 0.05 and p < 0.01, respectively). There was no significant difference in LTB4 and LTC4 production between patients with inactive CD and controls. In both patients with active CD and controls, no difference in LTB4 and LTC4 production was observed between the patients with and without diarrhoea. These findings suggest that enhanced generation of LTB4 and LTC4 in the small intestinal mucosa may contribute to the pathophysiology of CD but would not be related to the development of diarrhoea.

A specific assay for leukotriene B4 in human whole blood

Leukotrienes (LTs) are potent mediators of inflammatory and allergic responses, and are present in biological fluids in minute amounts, that is, in the picogram range. The aim of this study was to develop and validate a method for determination of LTB4 synthesized in vitro in human whole blood. Heparinized blood was stimulated with calcium-ionophore A23187 at 37 degrees C. After 30 min cells were separated by centrifugation. LTB4 was analyzed by radioimmunoassay (RIA). When sample preparation was restricted to protein precipitation with acetone, interference was demonstrated by lack of parallelism between standard and sample dilution curves. Purification was, therefore, extended by combinations of the following steps: 1) protein precipitation, 2) lipid extractions, and 3) high-performance liquid chromatography (HPLC). One of two commercially available LTB4 standards was found to contain multiple components, several of which were immunoreactive in RIA. Even for the standard containing pure LTB4, interference was demonstrated by lack of parallelism between sample and standard dilution curves. Testing eight combinations of varying purification steps, we found that only a three-step purification procedure, including 1) solid-phase extraction, 2) protein precipitation at -20 degrees C, and 3) HPLC, was able to eliminate interference in RIA. Using this procedure, the recovery was 78%. Stimulation of whole blood from normal subjects with calcium-ionophore showed optimal LTB4 production at 10 microM ionophore, yielding 6.6 ng LTB4/mL blood.

Profiling of eicosanoids in inflamed gall bladder wall by gas chromatography with selected-ion monitoring

The profiling of eicosanoids, including prostaglandin E2 (PGE2), prostaglandin F2 alpha (PGF2 alpha), 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha), thromboxane B2 (TXB2) and leukotriene B4 (LTB4), in dog and human gall bladders was carried out by a combination of an effective and convenient clean-up procedure and gas chromatography with selected-ion monitoring. The clean-up procedure was based on the stepwise elution of their methyl ester derivatives from a silica gel column with n-hexane-ethyl acetate and ethyl acetate-methanol in various ratios. The LTB4 methyl ester was eluted with an n-hexane-ethyl acetate (2:1, v/v) fraction because LTB4 is more lipophilic than the other eicosanoids. The present method permitted the quantitation of trace amounts of eicosanoids, including LTB4, present in tissues in the order of pg/mg of protein, without interference from other endogenous substances. In experimental acalculous cholecystitis produced in dog, the levels of eicosanoids (except LTB4) were significantly changed. Of these eicosanoids, the level of 6-keto-PGF1 alpha was significantly higher in the seromuscular layer and correlated with the observed severe morphological changes. In human chronic cholecystitis with gallstones, the level of 6-keto-PGF1 alpha in the mucosal layer was significantly higher than that in the seromuscular layer. These data suggest that prostaglandin I2 may play an important pathophysiological role in the course of cholecystitis.

Identification of guinea pig eosinophil chemotactic factor of anaphylaxis as leukotriene B4 and 8(S),15(S)-dihydroxy-5,9,11,13(Z,E,Z,E)-eicosatetraenoic acid

We have purified and characterized the guinea pig eosinophil chemotactic factor of anaphylaxis (ECF-A), an activity previously described in diffusates from sensitized lung challenged with specific Ag that appeared to selectively attract eosinophils from mixed leukocyte populations. Time course studies showed that the release of ECF-A from challenged presensitized guinea pig lung fragments closely paralleled the release of immunoreactive leukotriene B4 (iLTB4) and histamine. However, the majority of ECF-A (greater than 80%) and iLTB4 (greater than 79%) was extractable with the lipid fraction from the methanol wash of Sep-Pak-extracted diffusate, whereas histamine remained in the aqueous phase. A comparable neutrophil chemotactic activity was also found in the methanol extracts of the anaphylactic diffusates. By using a combination of HPLC and specific RIA, greater than 60% of ECF-A was attributable to LTB4. A second eosinophil chemotactic activity was also identified and coeluted (on both reverse phase and straight phase HPLC) with the synthetic standard 8(S),15(S)-dihydroxy-5,9,11,13(Z,E,Z,E)eicosatetraenoic acid (8(S),15(S)-diHETE). This was confirmed as 8(S),15(S)-diHETE by gas chromatography-mass spectrometry. Platelet-activating factor and histamine had negligible activity for guinea pig eosinophils, compared with synthetic LTB4 (p less than 0.05, 10(-9) and 10(-8) M; p less than 0.01, 10(-7) to 5 x 10(-6) M). In addition, synthetic 8(S),15(S)-diHETE had 3 times less activity than LTB4 at optimal chemotactic concentrations (10(-6) and 10(-7) M, respectively). Thus, guinea pig ECF-A appears to be largely attributable to lipoxygenase products of arachidonic acid, namely LTB4 and 8(S),15(S)-diHETE. Because guinea pig ECF-A was equally active on neutrophils (greater than 96% purity), it can no longer be considered a selective eosinophil chemoattractant.

Metabolism of arachidonic acid in neutrophils from alloxan-diabetic rabbits

The production of 5-lipoxygenase products from arachidonic acid was investigated in polymorphonuclear leukocytes (PMNL) isolated from non-diabetic and alloxan-induced diabetic rabbits: (i) production of 5-hydroxyeicosatetraenoic acid, leukotriene B4, and the two 6-trans-leukotriene B4 isomers were significantly decreased in the PMNL of diabetic rabbits when compared to non-diabetic rabbits; (ii) production of LTB4 and 5-HETE from diabetic PMNL required the addition of Ca2+ and A23187 to a greater degree than control incubations; and (iii) the availability of substrate in the PMNL of diabetics was not a limiting factor for 5-lipoxygenase product formation. Alternative pathways of arachidonic acid metabolism were also evaluated: the recovery of exogenous leukotriene B4 and 5-hydroxyeicosatetraenoic acid were identical using PMNL from control and diabetic rabbits and peptido-leukotrienes were not detected by radioimmunoassay. The data suggest that the activity of 5-lipoxygenase and the production of 5-hydroperoxyeicosatetraenoic acid in the diabetic PMNL may be limiting factors since the formation of leukotriene B4, leukotriene B4 isomers, and 5-hydroxyeicosatetraenoic acid are depressed in PMNL of diabetic rabbits. Alternative pathways do not account for the conversion of arachidonic acid to other products nor are the elimination pathways for LTB4 and 5-HETE different. Decreased formation of 5-hydroxyeicosatetraenoic acid and leukotriene B4 could predispose diabetic subjects to infection due to a decrease in mediators leading to the local accumulation of PMNL in the inflammatory response.

Gas chromatographic-mass spectrometric analysis of lipoxygenase products in post-ischemic rabbit myocardium

Leukotriene B4 (LTB4) is a potent chemotactic compound for neutrophils and is thought to be an important mediator of myocardial ischemia-reflow injury. We have measured LTB4 in rabbit cardiac tissue following ischemia-reflow using a sensitive and specific gas chromatographic-mass spectrometric (GC-MS) assay. The concentration of LTB4 in rabbit myocardium following 45 min ischemia and 3 h reflow was 48.7 +/- 12.5 pg/g, significantly higher than in non-ischemic tissue from the same animal (17.5 +/- 3.9 pg/g). These concentrations were at least an order of magnitude lower than previously reported values assessed by radioimmunoassay (RIA). Compared with the GC-MS method, RIA greatly overestimated LTB4 concentrations in cardiac tissue. The capacity of post-ischemic myocardium to produce lipoxygenase products, LTB4, 5-, 12- and 15-HETEs was also assessed following incubation of myocardium ex vivo with calcium ionophore. In all animals ischemic cardiac tissue produced greater amounts of LTB4, 5-, and 12-HETEs than non-ischemic myocardium and 12-HETE was the major product. Neutrophils that have accumulated in the injured tissue may be a major source of these products. However, in contrast to cardiac tissue, isolated rabbit neutrophils stimulated with A23187 produced 5-HETE as the major product with very little 12-HETE formed. These latter findings suggest that cells other than neutrophils may contribute to the production of lipoxygenase products during myocardial ischemia-reflow injury.

Reduced neutrophil LTB4 release in atopic dermatitis patients despite normal fatty acid composition

Propositions about an abnormal fatty acid metabolism in atopic dermatitis patients prompted us to compare the phospholipid fatty acid composition and LTB4 release of neutrophils from 15 atopic dermatitis patients, as well as the adipose tissue triglyceride fatty acid composition, to that of 15 healthy controls matched by age, gender, and smoking habits. We found no differences in the tissue fatty acid composition between the two groups. The release of leukotriene B4 from Ca-ionophore-stimulated neutrophils in patients was on the average only 42% (p less than 0.001) of that measured in the control group, despite the very similar arachidonic acid contents of these cells. Our study does not support the assumption of an abnormal fatty acid desaturation in atopic dermatitis patients. Rather, the capacity to release and/or convert arachidonic acid into leukotrienes in neutrophils appears to be affected by this disease.

Simultaneous reversed-phase extraction of lipoxygenase and cyclooxygenase metabolites of arachidonic acid in nasal secretions: methodological aspects

An improved analytical method for the simultaneous solid-phase extraction of arachidonic acid metabolites in biological samples is described. The major aim of the work was to define the cause of the different recoveries reported in the literature for leukotrienes and hydroxyeicosatetraenoic acids. We used nasal lavages to carry out a comparative study of solid-phase extraction parameters of practical importance in securing good recoveries of leukotrienes and hydroxyeicosatetraenoic acids from biological samples. We evaluated the influence of the pH of the sample, the pH of the water used to wash the extraction cartridge before elution of the adsorbed analytes, the comparative behaviour of commercially available octadecyl adsorbents and the influence of the concentration-evaporation step on final recoveries. Data thus obtained show that there is no significant difference in results when the samples and the water used to wash the cartridge before analyte elution are adjusted to pH values ranging between 4.0 and 7.4. Below pH 4.0, losses may be significant. Furthermore, recoveries can be very much dependent on the type of solid-phase cartridge material and on the eluent evaporation method, especially with regard to aqueous phase removal.

Metabolism of leukotriene B4 in isolated rat hepatocytes. Involvement of 2,4-dienoyl-coenzyme A reductase in leukotriene B4 metabolism

Radiolabeled leukotriene (LT) B4 was incubated with isolated rat hepatocytes in order to assess the metabolism of this chemotactic leukotriene by the liver. At least eight radioactive metabolites were observed, three of which were previously identified as 20-hydroxy-, 20-carboxy-, and 18-carboxy-19,20-dinor-LTB4. A less lipophilic major metabolite (designated HIV) was purified by two reverse phase high performance liquid chromatography separations and was found to exhibit maximal UV absorbance at 269 nm with shoulders at 260 and 280 indicating the presence of a conjugated triene chromophore. Negative ion electron capture gas chromatography/mass spectrometry analysis of the pentafluorobenzyl ester, trimethylsilyl ether derivative of HIV, and positive ion electron ionization mass spectra of the methyl ester trimethylsilyl derivative were consistent with a structure of this metabolite being 16-carboxy-14,15-dihydro-17,18,19,20-tetranor-LTB3. The appearance of this metabolite supports the concept of further beta-oxidation of LTB4 to the carbon 16 which requires the action of 2,4-dienoyl-CoA reductase to remove the 14,15-double bond located two carbon atoms removed from the CoA thioester moiety. One minor metabolite was analyzed by negative ion continuous flow fast atom bombardment mass spectrometry which revealed an ion at m/z 444 which by high resolution mass spectrometry was shown to contain both nitrogen and sulfur. Tandem mass spectrometry suggested the presence of SO3- as well as other fragments corresponding to the amino acid taurine. Incubation of isolated rat hepatocytes with [14C]taurine as well as [3H]LTB4 revealed the incorporation of both radioactive isotopes into this metabolite. The data supported the identification of this metabolite as tauro-18-carboxy-19,20-dinor-LTB4. Amino acid conjugation of leukotrienes has not been previously reported and suggests that such intermediates might participate in enterohepatic circulation of LTB4 metabolites in the intact animal and thus serve as an alternative metabolic route for LTB4 elimination.

The mechanism of leukotriene B4 export from human polymorphonuclear leukocytes

Recently, we characterized the export of leukotriene (LT) C4 from human eosinophils as a carrier-mediated process (Lam, B. K., Owen, W. F., Jr., Austen, K. F., and Soberman, R. J. (1989) J. Biol. Chem. 264, 12885-12889). To determine whether a similar mechanism regulates the release of leukotriene B4 (LTB4), human polymorphonuclear leukocytes (PMN) were preloaded with LTB4 by incubation with 25 microM leukotriene A4 (LTA4) at 0 degrees C for 60 min. PMN converted LTA4 to LTB4 in a time-dependent manner as determined by resolution of products by reverse-phase high performance liquid chromatography and quantitation by integrated optical density. When PMN preloaded with LTB4 were resuspended in buffer at 37 degrees C for 0-90 s, there occurred a time-dependent release of LTB4 but little formation or release of 20-hydroxy-LTB4 and 20-carboxy-LTB4. When PMN were preloaded with increasing amounts of intracellular LTB4 by incubation with 3.1-50.0 microM LTA4 and were then resuspended in buffer at 37 degrees C for 20 s, there occurred a concentration-dependent and saturable release of LTB4 with a Km of 798 pmol/10(7) cells and a Vmax of 383 pmol/10(7) cells/20 s. The release of LTB4 was temperature-sensitive with a Q10 of 3.0 and an energy of activation of 19.9 kcal/mol. The rate of LTB4 release at 37 degrees C is about 50 times the rate of 20-carboxy-LTB4 release. PMN preloaded with LTB4 and resuspended at 0 degree C for 1-60 min in the presence of 30 microM LTA5 progressively converted LTA5 to LTB5. The rate of LTB4 release at 0 degree C was inhibited over the entire time period, peaking at about 50% at 30 min. These results indicate that the release of LTB4 from PMN is a carrier-mediated process that is distinct from its biosynthesis.

Cellular LTB4 production differs in allergic sheep with and without late airway responses

We tested the hypothesis that allergic sheep that develop both early and late airway responses to inhaled Ascaris suum antigen (late responders) have an increased capacity to generate leukotrienes (LTs) compared with allergic sheep that show only early responses to inhaled antigen (acute responders). To test this hypothesis, we measured LTB4 production, in vitro, by granulocytes isolated from peripheral blood and by macrophages isolated from bronchoalveolar lavage (BAL) from both groups of sheep greater than or equal to 2 wk after the animal's last antigen challenge; LTB4 production by granulocytes isolated from BAL from both groups of sheep 6 and 48 h after local airway challenge with A. suum antigen was also measured. LTB4 production was induced by incubating cells (i.e., either granulocytes or macrophages) with calcium ionophore (A23187, 2 microM) and arachidonic acid (30 microM). LTB4 production was quantitated by high-performance liquid chromatography and verified by radioimmunoassay (RIA). On stimulation peripheral blood granulocytes from late responders (n = 7) produced (means +/- SD/10(6) cells) 13.3 +/- 5.2 ng LTB4 compared with 5.3 +/- 1.5 ng LTB4 (P less than 0.05) for acute responders (n = 7). This increased LTB4 production did not result from variations in granulocyte differential or cyclooxygenase activity (as indicated by RIA measurements of prostaglandin E2 production).(ABSTRACT TRUNCATED AT 250 WORDS)

Single-step organic extraction of leukotrienes and related compounds and their simultaneous analysis by high-performance liquid chromatography

A method for the simultaneous single-step organic extraction from biological matrices of peptido- and dihydroxyleukotrienes as well as 5-hydroperoxy- and 5-hydroxyeicosatetraenoic acid followed by separation and quantitation in a single run on reversed-phase high-performance liquid chromatography was evaluated. Using an extraction system comprising 400/1200/4800 (v/v/v) aqueous phase/isopropanol/dichloromethane, pH 3.0, absolute recoveries of 82.3 +/- 2.0, 89.7 +/- 1.0, 93.7 +/- 1.4, 92.8 +/- 1.4, 90 +/- 4, and 90 +/- 4% for prostaglandin B1 (PGB1), leukotriene C4 (LTC4), leukotriene B4 (LTB4), leukotriene D4 (LTD4), 5-hydroperoxyeicosatetraenoic acid (5-HETE), respectively, were achieved. Separation and quantitation of products were performed on a Nucleosil 100 C18 column (5 microns, 4.6 X 250 mm) using, at pH 6.0, a gradient system comprising 72/28/0.02 (v/v/v) methanol/water/glacial acetic acid from 0 to 15 min, followed by a convex gradient to 76/24/0.02 (v/v/v) methanol/water/glacial acetic acid, followed by a 10-min hold at this methanol concentration. The method was used to investigate the profile of leukotrienes synthesized by rat hepatocyte homogenates from 5-HPETE or leukotriene A4 in absence or presence of glutathione (GSH). During a 5-min incubation with 100 microM 5-HPETE, 9.6 ng LTB4/mg protein and 2.2 micrograms 5-HETE/mg protein were formed in the absence of GSH. In the presence of 0.4 mM GSH, 3.7 ng LTB4/mg protein and 11.0 micrograms 5-HETE/mg protein were formed. Using 20 microM LTA4 as a substrate, 17.3 and 324.0 ng LTC4/mg protein X min and 14.3 and 19.3 ng LTB4/mg protein X min were formed in the presence of 0.4 and 10 mM GSH, respectively.

Identification and biological activity of dihydroleukotriene B4: a prominent metabolite of leukotriene B4 in the human lung

Exogenous [3H]leukotriene B4 (LTB4) was converted into several polar and non-polar metabolites in the chopped human lung. One of the major metabolites was identified as 5(S),12-dihydroxy-6,8,14-eicosatrienoic acid (10,11-dihydro-LTB4) by means of co-chromatography with authentic standards, ultraviolet spectrometry and gas chromatography-mass spectrometry. Analysis of chiral straight phase HPLC revealed the presence of both the 12(S) and 12(R) epimers of dihydro-LTB4. Dihydro-LTB4 was also formed from endogenously generated LTB4 in ionophore A23187 stimulated incubations. The dihydro metabolites were approximately 100 times less potent than LTB4 in causing guinea pig lung strip contraction and leukocyte-dependent inflammation in the hamster cheek pouch in vivo.

Hepatic uptake and metabolic disposition of leukotriene B4 in rats

1. In isolated perfused rat liver and in vivo, up to 25% of [3H]leukotriene B4 was eliminated from the circulation via hepatic uptake and biliary excretion within 1 h. Total body recovery of 3H amounted to about 60% of infused [3H]leukotriene B4. 2. Hepatobiliary excretion of leukotriene B4 and its metabolites exceeded renal elimination by about 4-fold and depended, in contrast with excretion of cysteinyl leukotriene E4, upon continuous taurocholate supply. 3. Analyses of bile, liver and recirculated perfusate using h.p.l.c. indicated that the liver metabolized leukotriene B4 extensively to omega-carboxyleukotriene B4 and its beta-oxidized derivatives, and no unmetabolized leukotriene B4 appeared in bile. These results substantiate the important contribution of the hepatobiliary system with respect to the metabolic fate of leukotriene B4.

Prostaglandin and leukotriene production by alveolar type II cells in vitro

Alveolar type II cells were isolated from adult rats, cultured for 22 h, and individual eicosanoids in the media from unstimulated and stimulated cells were quantified by immunoassay. Stimulation with the calcium ionophore A23187 significantly increased the media levels of prostaglandins (prostaglandin and 6-keto-prostaglandin F1 alpha greater than thromboxane B2). In contrast to previous reports, increased media levels of leukotrienes were also recovered from cells incubated with A23187, but only for cells in culture for less than or equal to 24 h. The production of leukotriene C4 was confirmed by a combination of high-performance liquid chromatography and spectrophotometric analysis. The profile of eicosanoids produced by cultures of alveolar type II cells was distinctly different than that of similarly cultured alveolar macrophages. Finally, stimulation of alveolar type II cell cultures with either a phorbol ester or phospholipase C increased media prostaglandin levels but failed to increase leukotriene levels. We conclude that primary cultures of alveolar type II cells are capable of the de novo metabolism of arachidonic acid to both cyclooxygenase and lipoxygenase products and that the production of leukotrienes is dependent on both time in culture and agonist. Thus alveolar type II cells are a potential source for the production of these eicosanoids in vivo, and the particular lipid mediators produced may vary depending on the pathophysiologic stimulus.

Release of leukotriene B4 from rat Kupffer cells

In order to examine the production of leukotriene B4 (LTB4) from Kupffer cells, Kupffer cells isolated from the normal rat liver were incubated with calcium ionophore A23187, opsonized zymosan, or platelet activating factor (PAF), and the amount of LTB4 in the culture supernatant was determined by the combined technique of reverse-phase high-performance liquid chromatography and radioimmunoassay. As a result, when activated in vitro with calcium ionophore A23187, Kupffer cells generated LTB4. When Kupffer cells were stimulated with calcium ionophore after 10-min preincubation with AA861, a selective 5-lipoxygenase inhibitor, the release of LTB4 from Kupffer cells was markedly suppressed. PAF, which is a phospholipid mediator having a wide spectrum of biological activities, significantly enhanced the release of LTB4 from Kupffer cells stimulated with calcium ionophore or opsonized zymosan. Even when the Kupffer cell were not stimulated with calcium ionophore or opsonized zymosan, LTB4 production was significantly increased by PAF. Thus, our studies indicate that Kupffer cells could generate LTB4 as well as polymorphonuclear leukocytes and macrophages. In addition, it is suggested that Kupffer cells may be able to modify inflammatory and immunological events in the liver tissue by the release of LTB4.

Three new and bioactive icosanoids from the temperate red marine alga Farlowia mollis

Three new dihydroxyicosanoids, 12(R),13(R)-dihydroxyicosa-5(Z),8(Z),10(E),14(Z)-tetraenoic acid, 12(R),13(R)-dihydroxyicosa-5(Z),8(Z),10(E),14(Z),17(Z)-pentaeno ic acid and 10(R*),11(R*)-dihydroxyoctadeca-6(Z),8(E),12(Z)-trienoic acid, have been isolated from a previously unstudied temperate red marine alga, Farlowia mollis (Cryptonemiales, Rhodophyta). The structures of these new metabolites have been deduced from detailed nuclear magnetic resonance and mass spectrometry analyses on stabilized diacetate-methyl esters and stereochemistry deduced by 1H NMR couplings and CD analysis of a dibenzoate derivative. Collectively, these new natural products modulate fMLP-induced superoxide anion generation in human neutrophils, inhibit the conversion of arachidonic acid to lipoxygenase products by human neutrophils, and inhibit the functioning of the dog kidney Na+/K+ ATPase.

Radioimmunoassay of LTB4 in plasma from different species: a cautionary note

In clinical and pre-clinical research the pharmacodynamics of selective 5-lipoxygenase and dual 5-lipoxygenase/cyclo-oxygenase inhibitors may be studied by direct RIA of plasma LTB4. Although immunoreactive LTB4 in plasma from A23187 stimulated human blood has the characteristics of authentic LTB4 our results show, particularly in mice and rats, that exposure to A23187 produces large quantities of 12-HETE. Since in different species the levels of 12-HETE increase with platelet concentration we suggest that the 12(S)-HETE is produced by platelet lipoxygenase. However, we do not rule out the possibility that a proportion of 12-HETE may exist as the (R)-stereoisomer. The latter has greater potential for interference in the direct RIA of LTB4. Biosynthesis of 12-HETE may be measured either by RPHPLC/U.V. abs. (8) or by RIA (9) and LTB4 by a more specific antibody described in this report. We conclude that the combined ex vivo RIA of plasma TXB2, LTB4 and 12-HETE has utility in determining the selectivity of inhibitors of arachidonate metabolism and in distinguishing between selective 5-lipoxygenase inhibitors which interact directly with the enzyme and anti-oxidant or free radical scavenging types which may be less specific.

Hydroxylation of leukotriene B4 in leukocytes from various species: identification of a metabolite to authentic 5S,12R,19-trihydroxy-6Z,8E,10E,14Z-eicosatetra enoic acid and relative importance of 19- and 20-hydroxylations

The major hydroxylated metabolite of leukotriene B4 in rat PMNL was found identical (UV spectrum and retention times in 3 different HPLC systems) to a synthetic compound of known stereochemistry, 19-hydroxy-LTB4. PMNL from various species exhibited 3 different types of behaviour for LTB4 hydroxylation. Human and monkey PMNL showed a high hydroxylating activity and a high regioselectivity with almost exclusive formation of products from 20-hydroxylation. Rat and mini-pig PMNL exhibited a very different regioselectivity with major formation of 19-OH-LTB4 (3:1 ratio). Finally, pig and beef PMNL were found almost devoid of any hydroxylating activity toward LTB4.

Hydrogen peroxide inhibits alveolar macrophage 5-lipoxygenase metabolism in association with depletion of ATP

We have previously shown that the biologically important reactive oxygen metabolite hydrogen peroxide (H2O2) stimulates arachidonic acid (AA) release and thromboxane A2 synthesis in the rat alveolar macrophage. We have now investigated the effects of H2O2 on alveolar macrophage 5-lipoxygenase metabolism. H2O2 failed to stimulate detectable synthesis of leukotriene B4, leukotriene C4, or 5-hydroxyeicosatetraenoic acid (5-HETE) as determined by reverse-phase high performance liquid chromatography (RP-HPLC) and sensitive radioimmunoassays (RIAs). This was not explained by oxidative degradation of leukotrienes by H2O2 at the concentrations used. Moreover, RIA and RP-HPLC analyses demonstrated that H2O2 dose-dependently inhibited synthesis of leukotriene B4, leukotriene C4, and 5-HETE induced by the agonists A23187 (10 microM) and zymosan (100 micrograms/ml), over the same concentration range at which it augmented synthesis of the cyclooxygenase products thromboxane A2 and 12-hydroxy-5,8,10-heptadecatrienoic acid. Four lines of evidence suggested that H2O2 inhibited alveolar macrophage leukotriene and 5-HETE synthesis by depleting cellular ATP, a cofactor for 5-lipoxygenase. 1) H2O2 depleted ATP in A23187- and zymosan-stimulated alveolar macrophages with a dose dependence very similar to that for inhibition of agonist-induced leukotriene synthesis. 2) The time courses of ATP depletion and inhibition of leukotriene B4 synthesis by H2O2 were compatible with a rate-limiting effect of ATP on leukotriene synthesis in H2O2-exposed cultures. 3) Treatment of alveolar macrophages with the electron transport inhibitor antimycin A prior to A23187 stimulation depleted ATP and inhibited leukotriene B4 and C4 synthesis to equivalent degrees, while thromboxane A2 production was spared. 4) Incubation with the ATP precursors inosine plus phosphate attenuated both ATP depletion and inhibition of leukotriene B4 and C4 synthesis in alveolar macrophages stimulated with A23187 in the presence of H2O2. Our results show that H2O2 has the capacity to act both as an agonist for macrophage AA metabolism, and as a selective inhibitor of the 5-lipoxygenase pathway, probably as a result of its ability to deplete ATP. Depletion of cellular energy stores by oxidants generated during inflammation in vivo may be a means by which the inflammatory response is self-limited.

Increased concentrations of leukotrienes in bronchoalveolar lavage fluid of patients with ARDS or at risk for ARDS

The sulfidopeptide leukotrienes (LT) C4 and D4 have been reported to promote the formation of pulmonary edema when administered into the pulmonary circulation of laboratory animals. As a first step in the evaluation of the hypothesis that these leukotrienes participate in the edema formation of the adult respiratory distress syndrome (ARDS), we investigated whether LTC4 and LTD4 were present in the bronchoalveolar lavage (BAL) fluid of patients with ARDS compared to nonsmoker control subjects and to patients with acute respiratory failure exhibiting no radiographic evidence of widespread pulmonary infiltrates but having a clinical predisposition for developing ARDS, i.e., the "at risk" group. Bronchoscopic lavage was performed with sterile 0.9% NaCl on 32 control subjects, nine patients with ARDS, and nine patients "at risk" for ARDS. Leukotrienes were measured in BAL fluid by radioimmunoassay after methanol extraction and HPLC purification of a 20-ml aliquot of the BAL sample. LTC4 and LTD4 (mean +/- SE) increased from 1.1 +/- 0.2 and 1.2 +/- 0.5 ng/lavage in the BAL fluid of control subjects to 6.3 +/- 2.3 and 20.1 +/- 5.9 ng/lavage in patients "at risk" for ARDS and to 12.5 +/- 3.0 and 30.5 +/- 7.8 ng/lavage in patients with ARDS, respectively. The sulfidopeptide LTs correlated with BAL fluid protein content. These results suggest that increased amounts of LTs in BAL fluid are a general finding in patients with ARDS and those "at risk" for ARDS.

Chemotactic activity in inflammatory bowel disease. Role of leukotriene B4

An important histologic feature of inflammatory bowel disease (IBD) is infiltration of the colonic mucosa with neutrophils. To investigate the nature of the chemotactic agents responsible for this infiltration, colonic mucosa from three normals and nine patients with inflammatory bowel disease (seven ulcerative colitis, two Crohn's colitis) was assayed for chemotactic activity for human neutrophils in vitro in a Boyden chamber. There was more (greater than 10-fold more) chemotactic activity in homogenates of inflammatory bowel disease mucosa than in homogenates of normal colonic mucosa. Analysis of the chemotactic activity in the inflammatory bowel disease mucosa revealed that most was lipid extractable. Moreover, when the lipid extract was fractionated by reverse-phase high-pressure liquid chromatography, the only fraction with significant chemotactic activity was the fraction that coeluted with leukotriene B4. The chemotactic response to IBD mucosa was blocked by anti-LTB4 antisera. The amount of chemotactic activity in lipid extracts of different inflammatory bowel disease specimens correlated well with the concentration of leukotriene B4 measured by UV absorbance (250 ng/g of mucosa). These data suggest that leukotriene B4 is an important stimulus to neutrophil chemotaxis in inflammatory bowel disease and, thus, may play a major role in the amplification of the inflammatory response in this condition.

Single-step procedure for the extraction and purification of leukotrienes B4, C4 and D4

A rapid and simple method for the on-line concentration and high-performance liquid chromatographic (HPLC) purification of the leukotrienes in good yield from biological fluids is described. Readily available antisera are used in conjunction with this system to give a specific and sensitive assay for leukotrienes B4, C4 and D4 with sub-nanogram limits of detection. Tritium-labelled leukotrienes are used as internal standards, both to locate the leukotrienes post-HPLC and to accurately determine recoveries.

Precolumn extraction and reversed-phase high-pressure liquid chromatography of prostaglandins and leukotrienes

Prostaglandins, leukotrienes, and other metabolites of arachidonic acid can be conveniently and efficiently extracted from biological media using a precolumn containing octadecylsilyl silica connected to a 6-port switching valve that is in line with an analytical HPLC column. This procedure makes it possible to extract complex mixtures of eicosanoids and to analyze them by reversed-phase HPLC in a single step. The requirement to evaporate solvents from extracts prior to HPLC is therefore eliminated, saving time and reducing the possibilities for loss and contamination. The effects on recoveries of various media for loading the sample onto the precolumn were investigated, and it was concluded that 15% methanol at neutral pH gives the best overall results. It is therefore not necessary to acidity the sample prior to extraction, which simplifies the procedure and improves the recoveries of acid-labile eicosanoids. Following extraction, eicosanoids can be introduced onto the HPLC column by changing the position of the 6-port switching valve. We have investigated several approaches to the analysis of complex mixtures of these products by reversed-phase HPLC. The best results were obtained using a ternary gradient with a non-end-capped column of octadecylsilyl silica. Metabolites of arachidonic acid other than peptido-leukotrienes were first eluted by increasing the concentrations of acetonitrile and methanol in the mobile phase, which contained a constant concentration of trifluoroacetic acid (0.001%). Peptido-leukotrienes were then eluted with a second gradient, in which the concentrations of acetonitrile and methanol were kept constant, but the concentration of trifluoroacetic acid was increased to 0.0091%. Leukotrienes C4, D4, and E4 appear as sharp peaks at the end of the chromatogram and are completely separated from other types of arachidonic acid metabolites.

Leukotriene B4 catabolism: quantitation of leukotriene B4 and its omega-oxidation products by reversed-phase high-performance liquid chromatography

LTB4 and its omega-oxidation products may be rapidly, sensitively, and specifically quantitated by the methods of solid-phase extraction and reversed-phase high-performance liquid chromatography (HPLC), which are described in this chapter. Although other techniques, such as radioimmunoassay or gas chromatography-mass spectrometry, may be utilized for quantitative analysis of the lipoxygenase products of arachidonic acid, only the technique of reversed-phase HPLC can quantitate as many as 10 metabolites in a single analysis, without prior derivatization. In this chapter, we also reviewed the chromatographic theory which we utilized in order to optimize reversed-phase HPLC analysis of LTB4 and its omega-oxidation products. With this information and a gradient HPLC system, it is possible for any investigator to develop a powerful assay for the potent inflammatory mediator, LTB4, or for any other lipoxygenase product of arachidonic acid.

Colchicine inhibits ionophore-induced formation of leukotriene B4 by human neutrophils: the role of microtubules

Neutrophils which ingest particles (serum-treated zymosan, monosodium urate crystals) or are exposed to calcium ionophore A23187 generate leukotriene B4 (LTB4). Earlier work has shown that cells exposed to colchicine before exposure to monosodium urate crystals produce less LTB4; the formation of 5-HETE is unaffected. To determine whether inhibition by colchicine of LTB4 generation was stimulus-specific and was mediated by microtubule integrity, the effects of colchicine (10 microM, 60 min) on the release of lipoxygenase products from neutrophils exposed to ionophore A23187 (10 microM, 5 min) were examined. In the presence of exogenous arachidonic acid (100 microM, 15 min), colchicine decreased LTB4 to 48% +/- 11.7 of control and 5-HETE to 60.5% +/- 5.7 of control (mean +/- SEM); 15-HETE was also decreased to 61% +/- 10.3 of control. In the absence of exogenous arachidonate, LTB4 was decreased to 22.2% +/- 11.7 of control and 5-HETE to 13% +/- 4.8 of control. Lumicolchicine did not significantly affect formation of 5-HETE or LTB4. However, vinblastine sulfate (20 microM, 60 min), another microtubule-disruptive agent, decreased the formation of both 5-lipoxygenase products. The effects of colchicine and vinblastine were not due to impairment of cell viability because the release of cytoplasmic lactic dehydrogenase was unaffected. Ultrastructural analysis of centriolar microtubules showed that decrements in microtubule numbers of colchicine- and vinblastine-treated cells paralleled decrements in 5-lipoxygenase products. These pharmacologic manipulations suggested that functional microtubules might be required for optimal lipoxygenase activity. Consequently, we prepared neutrophil-derived cytoplasts, devoid of an intact microtubule system. No significant decreases in the 5- or 15-lipoxygenase products were found when cytoplasts were exposed to colchicine in the presence of exogenous arachidonate and A23187. The data show that colchicine inhibits the formation of lipoxygenase products from neutrophils stimulated with A23187, most likely via its effect on microtubules, the integrity of which appears necessary for full expression of 5- and 15-lipoxygenases.

Opsonized bacteria stimulate leukotriene synthesis in human leukocytes

Incubation of human leukocytes with opsonized bacteria led to leukotriene formation. The main products identified were leukotriene B4, 20-OH leukotriene B4 and 20-COOH leukotriene B4. A lesser amount of leukotriene C4 was formed. In contrast, only minor amounts of leukotrienes were formed by leukocytes challenged with uncoated bacteria. However, both opsonized and unopsonized bacteria stimulated the synthesis of 5S,12S-DHETE and 5S,12S,20-THETE. Opsonized bacteria caused a transient elevation of leukotriene B4 levels, with a maximum after 5 min. After 20 min of incubation the levels of 20-OH leukotriene B4, and 20-COOH leukotriene B4 were 7- and 20-times higher than those of leukotriene B4, showing that the leukocytes effectively degrade leukotriene B4 via omega-oxidation. In the light of the profound biological effects of leukotrienes, the present report indicates that leukotriene formation induced by opsonized bacteria might be important in the host defense against microorganisms.

Generation of leukotriene B4 and leukotriene E4 from porcine pulmonary artery

When chopped porcine pulmonary arteries were incubated with calcium ionophore A23187 (1) in the presence of indomethacin there was a time dependent generation of a substance which produced contractions of superfused strips of guinea-pig ileum smooth muscle (GPISM) which were indistinguishable from those induced by LTD4. This material however had a different retention time from LTD4 when subjected to HPLC and co-chromatographed with synthetic LTE4. In addition to LTE4 a substance which had properties indistinguishable from those of LTB4 when assayed on a combination of guinea-pig lung parenchymal strips (GPP) and GPISM (2) was generated from the pulmonary artery. This substance co-chromatographed with synthetic LTB4. The adventitia and intima were the richest source of LTE4, the adventitia releasing slightly more than the intima. The output of LTB4 and LTE4 was inhibited by 6,9-deepoxy-6,9-(phenylimino)-delta 6,8 prostaglandin I (U-60,257). Nordihydroguaiaretic acid (NDGA) inhibited the generation of LTE4.

The release of leukotriene B4-like material in biologically active amounts from the lesional skin of patients with psoriasis

The 5,12-dihydroxy metabolite of arachidonic acid, leukotriene B4, is a highly potent neutrophil chemoattractant. In view of the characteristic epidermal neutrophil infiltrate in psoriasis, the presence of leukotriene B4 in samples from untreated lesional and uninvolved skin has been sought. Chambers were fixed to abraded skin and filled with phosphate-buffered saline (PBS). After 35 min, the fluid was removed, and acidic lipids were extracted and subjected to high-performance liquid chromatography (HPLC). Extracts were purified by both straight- and reversed-phase HPLC, and assay of evaporated fractions by an agarose microdroplet chemokinesis technique indicated the presence of leukotriene B4-like material. No significant leukotriene B4-like activity was found in samples from uninvolved skin. Subsequent experiments using a modification of the initial skin chamber method indicated that leukotriene B4 was being released from deeper layers of lesional skin and not only from superficial scale. Monohydroxy-eicosatetraenoic acid-like activity was also seen in lesional samples as determined by straight-phase HPLC and chemokinesis assay. These findings and the proinflammatory properties of these compounds in human skin suggest that they may play a role in the pathogenesis of the psoriatic neutrophil infiltrate.

Identification of chemotactic lipoxygenase products of arachidonate metabolism in psoriatic skin

Skin biopsies and scale extracts from 22 patients with psoriasis were examined for the presence of chemotactic lipoxygenase products of arachidonate metabolism. Heat-stable leukocyte chemotactic activity in aqueous extracts of 2-mm punch biopsies from involved and uninvolved patient skin was significantly elevated, compared to healed psoriatic skin and to skin of normal controls. Ether extracts (pH 3.0) from 13 mg of psoriatic scales contained a mean chemotactic activity corresponding to that of leukotriene B4, 5 X 10(-8) M. On reverse phase high-pressure liquid chromatography, the main chemotactic lipids in scale extracts were leukotriene B4 and 5-HETE. Since lipoxygenase products are potent mediators of inflammation, they may play an important role in the evolution and maintenance of psoriatic lesions.

Dexamethasone inhibits generation in inflammatory sites of the chemotactic activity attributable to leukotriene B4

Effects of dexamethasone on chemotactic activity to polymorphonuclear leukocytes (PMN) of a lipophilic fraction collected with the aid of octadecylsilyl silica cartridge from exudates of an allergic inflammation were investigated. The chemotactic activity of this fraction was attributable to leukotriene B4 fraction separated by means of a reversed phase high performance liquid chromatography. Local application of dexamethasone suppressed dose-dependently the chemotactic activity of the lipophilic fraction in parallel with the inhibition of PMN infiltration in the inflammatory sites.

Characterization and biologic properties of 5,12-dihydroxy derivatives of eicosapentaenoic acid, including leukotriene B5 and the double lipoxygenase product

Leukotriene B5 (LTB5) and three stereoisomers were prepared biosynthetically from eicosapentaenoic acid and compared with the analogous derivatives of arachidonic acid for their chemotactic and aggregating effects on human neutrophilic polymorphonuclear leukocytes. Leukotriene B4 (LTB4), LTB5, and the 6-trans-diastereoisomers of each were generated by activating polymorphonuclear leukocytes with the calcium ionophore A23187 in the presence of 14C-labeled and unlabeled arachidonic acid or 14C-labeled and unlabeled eicosapentaenoic acid, respectively. The double lipoxygenase products, (5S,12S)-6-trans-8-cis-LTB4 and (5S,12S)-6-trans-8-cis-LTB5, were generated from 5S-hydroxyeicosatetraenoic acid and racemic 5-hydroxyeicosapentaenoic acid intermediates by incubation with platelet sonicates. The products of each reaction were isolated by reverse-phase-high performance liquid chromatography and identified by their retention times relative to the appropriate totally synthetic standards, ultraviolet absorption spectra, immunoreactivity in a radioimmunoassay for LTB4, and, for all but the double lipoxygenase products, by incorporation of radiolabel from the specific polyunsaturated fatty acid source. When the concentration of LTB5 eliciting maximum chemotactic response of human polymorphonuclear leukocytes, 50 ng/ml (1.5 X 10(-7) M), and that eliciting a maximum aggregation response, 20 ng/ml (5.9 X 10(-8) M), were compared with the interpolated values of LTB4 eliciting comparable effects, the potency of LTB5 relative to LTB4 was approximately 1:8 as a chemotactic agent and about 1:20 as an aggregating agent. The double lipoxygenase products and the resolved 6-trans-diastereoisomers of the pentaene and tetraene series were about 2 logs less active as chemotactic factors than LTB4 and only (5S,12S)-6-trans-8-cis-LTB4 had even minimal aggregating activity.

Biosynthesis and biological activity of leukotriene B5

Several studies indicate that increased intake of eicosapentaenoic acid (EPA) in the diet may lead to decreased incidence of thrombotic events. Most investigators agree that this is achieved by competitively inhibiting the conversion of arachidonic acid (AA) to thromboxane A2 in the platelets. The effect of high EPA-intake on the formation of prostacyclin is less clear. However, EPA is a good substrate for lipoxygenase enzymes which results in formation of hydroperoxy- and hydroxy-acids, and, in some cases, leukotrienes. The biological activities of the leukotrienes derived from arachidonic acid suggest that they mediate or modulate some symptoms associated with inflammatory and hypersensitivity reactions. In order to clarify the possible effect of dietary manipulation on inflammatory processes, leukotriene B5 (LTB5) was prepared and its biological activities assessed. LTB5 was biosynthesized by incubation EPA with glycogen-elicited polymorphonuclear neutrophils (PMN) from rabbits in the presence of the divalent cation ionophore, A23187. The LTB5 was extracted from the incubate using mini-reverse phase extraction columns (Sep-pak) and purified by reverse-phase high pressure liquid chromatography (RP-HPLC). The purity of the product assessed by repeat RP-HPLC and straight phase (SP) HPLC was greater than 95%. Ultra-violet spectrophotometry of the product confirmed its purity and also provided assessment of the yield. The biological activity of LTB5 was assessed and compared with that of LTB4 in the following tests: aggregation of rat neutrophils, chemokinesis of human PMN, lysosomal enzyme release from human PMN and potentiation of bradykinin-induced plasma exudation. In all these tests, LTB5 was considerably less active (at least 30 times) than LTB4.

Synthesis of leukotriene B4, and prostanoids by human alveolar macrophages: analysis by gas chromatography/mass spectrometry

Human alveolar macrophages, obtained during diagnostic bronchoscopy, were maintained in monolayer culture. Challenge of these cells (greater than 95% purity) with 1.2 mg/ml zymosan A particles (opsonized with human serum) was followed by a rapid release of leukotriene B4 into the medium, 7.28 +/- 5.99 ng/mg cell protein at 2 h (mean +/- S.D.4, n = 4). Leukotriene B4 was identified and measured by a novel technique employing capillary column gas chromatography coupled to negative ion chemical ionization mass spectrometry. The release of thromboxane B2, prostaglandins D2, E2, F2 alpha and the lysosomal enzyme N-acetyl-beta-D-glucosaminidase was also measured. Thromboxane B2 was the most abundant metabolite of arachidonic acid released into the culture medium (65.2 +/- 14.8 ng/mg cell protein 2 h after the addition of zymosan A, n = 4), and the synthesis of thromboxane B2 was inhibited by greater than 90% in 1 microM Na flurbiprofen. Inhibition of cyclooxygenase activity was accompanied by a 2-fold increase in leukotriene B4 synthesis.

Separation and quantitation of leukotrienes by reversed-phase high-performance liquid chromatography

A rapid and sensitive reversed-phase HPLC procedure is reported which allows the simultaneous separation and quantitation of LTC4, 11t-LTC4, LTD4, LTB4, 12epi,6t,8c-LTB4, 6t-LTB4 + 12epi,6t-LTB4, two trihydroxy-eicosatetraenoic acids tentatively identified as 20-OH-LTB4 and 20-OH,12epi,6t,8c-LTB4 and several not yet identified 15-series leukotrienes produced by the cytosol of porcine polymorphonuclear leukocytes.

Separation of major prostaglandins, leukotrienes, and monoHETEs by high performance liquid chromatography

A procedure using high performance liquid chromatography (HPLC) is described for the separation of major primary cyclooxygenase metabolites (prostacyclin metabolite-6ketoPGF1 alpha, thromboxane B2, and prostaglandins F2 alpha, E2, and D2), leukotrienes (C4, B4, and D4), monohydroxyeicosatetraenoic acids (15-, 11-, 12-, and 5HETEs), and free arachidonic acid. It is therefore possible to quantitate major arachidonic acid metabolites by a single chromatographic procedure. Using this technique we have determined that a major arachidonic acid metabolite of human lung macrophages co-elutes with leukotriene B4.

The separation of leukotrienes and hydroxyeicosatetraenoic acid metabolites of arachidonic acid by high performance liquid chromatography (HPLC)

The following high performance liquid chromatography system was found suitable for separating most lipoxygenase metabolites of arachidonic acid: Techsphere 5-C18 column, eluting solvent methanol:water:acetic acid (65:35:0.06 v/v), pH 5.3. Comparisons with other packing materials and solvent systems are described. The method could be used to identify lipoxygenase products released from mouse macrophage cells stimulated with gamma-hexachlorocyclohexane. Detection limits between 1 and 10 ng were obtained.

Human peritoneal macrophages synthesize leukotrienes B4 and C4

Macrophages were isolated from the dialysis fluid of patients undergoing continuous ambulatory peritoneal dialysis and separated by gradient centrifugation and purification on 50% Percoll. The cells were prelabeled with [14C]arachidonic acid for 1.5 h. The labeled cells were then incubated with calcium ionophore A23187 (1 microM), serum-treated zymosan (200 micrograms/ml), and a lipoxygenase inhibitor, nordihydroguairetic acid (1 X 10(-5) M). The arachidonate metabolites in the medium were separated on Sep-Pak columns, and finally purified by reverse-phase high-pressure liquid chromatography (HPLC). The labeled products co-chromatographed with authentic leukotriene B4 and leukotriene C4 standards. Serum-treated zymosan and A23187 significantly stimulated and nordihydroguairetic acid significantly inhibited leukotriene synthesis. Leukotriene D4 was not detected, which suggests that these cells contain low gamma-glutamyltranspeptidase or high dipeptidase activity. These results establish, for the first time, that human peritoneal macrophages synthesize the lipoxygenase products, leukotriene B4 and leukotriene C4.

Leukotrienes produced by incubation of dihomo-delta-linolenic acid with human polymorphonuclear leukocytes

Two new leukotrienes, 8,15-dihydroxy-9,11,13-icosatrienoic acid (8,15-LTB3) and 14,15-dihydroxy-8,10,12-icosatrienoic acid (14,15-LTB3) were identified in incubations of human polymorphonuclear leukocytes with dihomo-delta-linolenic acid (8,11,14-icosatrienoic acid). The yield of these compounds was very low (0.5% of the total radioactivity) and did not increase with indomethacin alone or in combination with ionophore A-23187. Stereochemistry and biologic activity of the two leukotrienes remain to be established.

A reevaluation of the chemotactic potency of leukotriene B4 (LTB4)

The chemotactic potency of leukotriene B4 (LTB4) was reevaluated based on an improved purification procedure which combines reversed phase and straight phase high pressure liquid chromatography (RP-HPLC and SP-HPLC). Socalled LTB4 isomer III prepared by RP-HPLC contains two double oxygenated 5,12-dihydroxy acids in addition to LTB4. On a molar basis, the chemotactic activity of LTB4 repurified by SP-HPLC was far greater than that of the other two 5,12-dihydroxy acids and comparable to that of formyl-methionyl-leucyl-phenylalanine (fMLP). The chemotactic activity of LTB4 isomer III is dependent upon the relative concentrations of the double oxygenated 5,12-dihydroxy acids and LTB4. Further purification of peak III by SP-HPLC is required before assessing the biologic activity of LTB4.

Rapid extraction of leukotrienes from biologic fluids and quantitation by high-performance liquid chromatography

Previous methods for the recovery and quantitation of leukotrienes have involved tedious extraction procedures, and high-performance liquid chromatographic (HPLC) techniques with significant limitations. We have designed a method to extract leukotrienes from biologic fluids using commercially available silica mini-columns requiring minimal preparation. Sample clarification is followed by a sensitive and reproducible HPLC technique which separates and quantifies the leukotrienes LTC4, LTD4, LTB4 (and at least three of their isomers). The entire procedure requires less than one hour per sample.