Leukotriene B4-induced human melanocyte pigmentation and leukotriene C4-induced human melanocyte growth are inhibited by different isoquinolinesulfonamides

Leukotriene C4 (LTC4) is known to be a potent mitogen for cultured human neonatal melanocytes. We now demonstrate that leukotriene B4 (LTB4) can induce pigmentation in cultured human neonatal melanocytes in a dose-dependent fashion. The LTC4-induced mitogenesis is blocked by the cyclic nucleotide-dependent kinase inhibitor N-[2-(methyl-amino)ethyl]-5-isoquinolinesulfonamide dihydrochloride (H8). The LTB4-induced pigmentation is blocked by the protein kinase C inhibitor 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H7). We propose that LTB4-induced pigmentation and LTC4-induced mitogenesis are important in vivo signals. Their different effects in our culture system are blocked by different protein kinase inhibitors.

Tandem mass spectrometry of negative ions from choline phospholipid molecular species related to platelet activating factor

Fast atom bombardment mass spectrometry of choline phospholipids produces negative ions characteristic of the intact molecule and tandem mass spectrometry of collision-induced decomposition of M-15 anions characterizes both the identity and substituent position of radyl groups. Certain choline phospholipid molecular species which may be of special interest in the generation of platelet activating factor contain a highly unsaturated fatty acyl substituent at sn-2 and an ether radyl group at sn-1; other choline phospholipid molecular species which contain esterified arachidonic acid are of interest as potential sources of arachidonate for eicosanoid biosynthesis. Collisional activated decomposition of 1-hexadecanoyl-2-arachidonoyl-sn-glycero-phosphocholine produce abundant carboxylate anions at m/z 303 (arachidonate) and m/z 255 (hexadecanoate) in a ratio of 3:1, diagnostic for the sn-2 arachidonoyl position. The ether analog, 1-O-hexadecyl-2-arachidonoyl glycerophosphocholine, produces only one collision-induced dissociation ion at m/z 303 and no product ions corresponding to the ether substituent at sn-1. Molecular weight information from the M-15 ion combined with the CID generated carboxylate anions completely characterize these important phospholipids. Precursor ion studies of M-15 anions from glycero-phosphocholine lipids indicate that this ion is derived directly from a unique adduct ion formed by attachment of the molecular species to a matrix alkoxide ion, neutralizing the positive charge of the quaternary choline nitrogen. Decomposition of this adduct ion yields a methylated matrix molecule and the nominal M-15 ion.

Metabolism of 12(R)-hydroxy-5,8,10,14-eicosatetraenoic acid (12(R)-HETE) in corneal tissues: formation of novel metabolites

12(R)-Hydroxy-5,8,10,14-eicosatetraenoic acid [12(R)-HETE], a cytochrome P450 arachidonate metabolite, is metabolized by corneal tissues via three distinct metabolic pathways: beta-oxidation, omega-hydroxylation, and keto-reduction. The major metabolite released from the intact rabbit corneal epithelium or cultured cells was identified by mass spectrometric analysis as 8-hydroxy-4,6,10-hexadecatrienoic acid, the tetranor metabolite derived following two steps of beta-oxidation from the carboxy terminus. The beta-oxidation pathway was expressed in both microsomes and mitochondria isolated from bovine corneal epithelium and was dependent on the addition of oxidizing equivalents. The major metabolite of 12(R)-HETE in subcellular fractions of bovine corneal epithelial cells was a dihydro compound, 12-hydroxy-5,8,14-eicosatrienoic acid (12-HETrE). This derivative is presumably formed by an oxidation of the hydroxyl group followed by two keto-reduction steps, since its formation was accompanied by the appearance of a keto metabolite identified as 12-oxo-5,8,14-eicosatrienoic acid. The omega-hydroxylation, in contrast to other cell types, was a minor route for 12(R)-HETE metabolism in these tissues. Since 12(R)-HETE has been implicated as a modulator of Na(+)-K(+)-ATPase activity and its related functions in ocular tissues, these findings raise the possibility that the newly described metabolites may be involved in regulating corneal functions. In addition, the presence of a keto reductase in the cornea may be of great importance following injury since 12(R)-HETrE resulting from 12(R)-HETE by this activity is a potent ocular proinflammatory compound.

Collisionally induced dissociation of epoxyeicosatrienoic acids and epoxyeicosatrienoic acid-phospholipid molecular species

Four isomers of epoxyeicosatrienoic acid (EET) can be formed by cytochrome P-450 oxidation of arachidonic acid: 5,6-, 8,9-, 11,12-, and 14,15-epoxyeicosatrienoic acid. The collision-induced dissociation of the [M-H]- anion at m/z 319 from each of these isomers, using negative-ion fast atom bombardment ionization and a triple quadrupole mass spectrometer, resulted in a series of common ions as well as ions characteristic of each isomer. The common ions were m/z 301 [M-H2O]- and 257 [M-(H2O + CO2)]-. Unique ions resulted from cleavages alpha to the epoxide moiety to form either conjugated carbanions or aldehydes. Mechanisms involving charge site transfer are suggested for the origin of these ions. A distonic ion series that may involve a charge-remote fragmentation mechanism was also observed. The epoxyeicosatrienoic acids were also incorporated into cellular phospholipids following incubation of the free acid with murine mast cells in culture. Negative fast atom bombardment mass spectrometry of purified glycerophosphoethanolamine-EET species and glycerophosphocholine-EET species yielded abundant [M-H]- and [M-CH3]- ions, respectively. The collision-induced dissociation of these specific high-mass ions revealed fragment ions characteristic of the epoxyeicosatrienoic acids incorporated (m/z 319, 301, and 257) and the same unique ions as those seen with each isomeric epoxyeicosatrienoic acid. With this direct method of analysis, phospholipids containing the four positional isomers of EET, including the highly labile (5,6-EET), could be identified as unique molecular species in mast cells incubated with EET.

Negative ion tandem mass spectrometry of leukotriene E4, and LTE 4, metabolites: Identification of LTE 4, in human urine

The sulfidopeptide leukotrienes, leukotriene E4, (LTE4,) and its N-acetyl derivative and several ω- and β-oxidized metabolites of LTE4, have been analyzed by tandem mass spectrometry. [M-H](-) ions were produced by continuous flow fast atom bombardment, and collision-induced dissociation of these ions was studied by using a triple quadrupole instrument. The product ion spectra obtained were characteristic of the structure of LTE4, and mechanisms of ion formation were investigated by using deuterated compounds. β-Elimination of the peptide portion of LTE4, by loss of CO2, and ethylene amine leaves the C-l carboxyl group ionized in the most abundant fragment ion for LTE4, and all metabolites. Tandem mass spectrometry of fast atom bombardment-generated anions from ω- and β-oxidized metabolites of LTE4, produced similar ions with only a minor influence of the third carboxyl group at the omega terminus evident. Tandem mass spectrometry was used to identify unequivocally the presence of unmodified LTE4, in a high performance liquid chromatography-purified fraction of urine from a normal healthy volunteer after infusion with LTE4.

Structural identification of cytochrome P450-dependent arachidonate metabolites formed by rabbit medullary thick ascending limb cells

The medullary thick ascending limb of Henle's loop (mTALH) contributes importantly to the regulation of extracellular fluid volume and composition and metabolizes arachidonic acid (AA) chiefly by a cytochrome P450 monooxygenase pathway. Rabbit mTALH cells, when incubated with radiolabeled [14C]AA, form products that segregate into two peaks designated P1 and P2 based on their reverse-phase high pressure liquid chromatography retention times. We have now definitively identified their chemical structures. mTALH cells, isolated from the rabbit outer medulla, were homogenized and incubated with [14C]AA in the presence of NADPH. The AA metabolites in P1 and P2 were identified by gas chromatographic-mass spectrometric methods, including fast atom bombardment, negative ion electron capture, and electron ionization. All mass spectrometric data, the lack of UV chromophores, and comparisons with authentic standards were consistent with P1 containing two principal components: 19-hydroxy-5,8,11,14 eicosatetraenoic acid (19-HETE) and 20 - hydroxy - 5,8,11,14 - eicosatetraenoic acid (20-HETE), P2 contained primarily 1,20-eicosa-5,8,11,14-tetraenedioic acid (20-COOH-AA). The biological properties of P1 and P2 were compared with those of the authentic standards of 19- and 20-HETE and 20-COOH-AA. P1 dose dependently relaxed precontracted mesenteric arterial rings, as did authentic (19S)- and (19R)-HETE, whereas 20-HETE relaxed at lower and contracted at higher concentrations. As P1 contained a mixture of 19- and 20-HETE, each of these AA metabolites presumably contributed to the vascular relaxation produced by P1. Neither P2 nor 20-COOH-AA exhibited vasoactivity, but each demonstrated a similar potency in inhibiting rabbit medullary Na(+)-K(+)-ATPase activity. As previously reported, P2 was a more potent inhibitor of Na(+)-K(+)-ATPase than P1. The lesser inhibitory activity of P1 presumably reflects the presence of similar amounts of 19-HETE, the least active metabolite, and 20-HETE, which resembles 20-COOH-AA in its capacity to inhibit Na(+)-K(+)-ATPase. Thus, the biological activity of the less polar peak, P1, can be accounted for by 19- and 20-HETE, and that of P2, by 20-COOH-AA.

Direct airway injury results in elevated levels of sulfidopeptide leukotrienes, detectable in airway secretions

Sulfidopeptide leukotrienes (LTC4/D4/E4) are suspected to be important lipid mediators in inflammatory responses in the lung. Previous investigations have provided evidence to support enhanced synthesis and secretion of these eicosanoids into bronchoalveolar lavage fluid in patients with Adult Respiratory Distress Syndrome (ARDS). We have prospectively examined the relationship between sulfidopeptide leukotriene levels in tracheal aspirates of 14 intubated and mechanically ventilated patients. When compared with the aspirate from one patient who required ventilation because of respiratory muscle weakness, the tracheal aspirates from eight ARDS patients had elevated leukotriene levels (range 2020-2052 pg/aspirate). However, the aspirates from four of the five patients with direct airway injury [inhalational burn (n = 3) and massive aspiration of gastric contents (n = 2)] contained significantly higher amounts of sulfidopeptide leukotrienes (range 10309-52244 pg/aspirate). Three of the five patients with direct airway injury did not develop ARDS. We conclude that simple aspiration of tracheal secretions can be used to monitor airway leukotriene biosynthesis in patients with lung injury and that elevated airway leukotriene levels may reflect airway epithelial damage, but may not predict the development of ARDS.

Molecular species analysis of arachidonate containing glycerophosphocholines by tandem mass spectrometry

Carboxylate anions arising from collision-induced dissociation (CID) of the [M - 15](-) ion produced by fast atom bombardment (FAB) of glycerophosphocholine (GPCho) were previously shown to be produced in an abundance ratio of 1:3 for the carboxylic acids esterified at sn - 1 and sn - 2, respectively. This observation has been confirmed in a series of 13 synthetic GPCho molecular species. A good correlation was found between the isomeric purity of GPCho molecular species as determined by negative-ion FAB/CID analysis and the isomeric purity of the sn - 2 fatty acid using a phospholipase A2 assay. Negative-ion FAB mass spectra of several 1-0-alkyl-2-acyl-GPCho molecular species were found to be similar to those of diacyl GPCho. However, the cm spectra from the major high-mass ions are different from those of the diacyl species in that the [M - 15](-) ion yields only one carboxylate anion and the [M - 86](-) undergoes a neutral loss of the sn - 2 carboxylic acid as a major decomposition product. These results suggest several rules useful for structural characterization of GPCho molecular species by negative-ion tandem mass spectrometry (MS/MS): (1) For diacyl species, the mass of the two carboxyl anions plus the mass of the GPeho backbone (minus a methyl group) must correspond to the mass of the [M - 15] anion; (2) for diacyl species there is a carboxylate anion ratio approximately 1:3 for the substituents at sn - 1 and sn - 2; and (3) for alkylether species, only one fatty acyl group is present, and the difference between the [M - 15] ion and the GPCho backbone (minus methyl) plus the fatty acyl group at sn - 2 corresponds to an alkylether substituent. (4) Assignment of ether-linked molecular species can be made from the [M - 86](-) ion, which has a strong neutral loss of the sn - 2 fatty acid.Analysis of GPCho isolated from human neutrophils by total lipid extraction and normal-phase HPLC was carried out by negative-ion FABand MS/MS. The major arachidonate-eontaining molecular species, which comprise only 5% of total GPCho, were identified by using precursor ion scans for the arachidonate anion, m/ z 303. Decomposition of identified. precursor ions permitted the assignment of those molecular species of GPCho that contain arachidonate at sn - 2 and identification of the substituent at the sn - 1 position. These results were compared to previously identified molecular species from human neutrophils. Several minor arachidonate-containing molecular species were tentatively identified.

Leukotriene E4 elimination and metabolism in normal human subjects

Radiolabeled leukotriene (LT) E4 was infused into three healthy subjects in order to assess the production and elimination of sulfidopeptide leukotriene metabolites in urine. Three different radiolabeled tracers were employed, [14,15-3H]LTE4, [35S]LTE4, and [14C] LTE4 in five separate infusion studies. There was a rapid disappearance of radioactivity from the vascular compartment in an apparent two-phase process. The first elimination phase had an apparent half-life of approximately 7 min. Radioactivity quickly appeared in the urine with 10-16% eliminated during the first 2 h following intravenous infusion; 7%, 2-5 h; 4%, 5-8 h; 4%, 8-15 h; and 1.5%, 15-24 h from the [14C] LTE4 experiments. Unmetabolized LTE4 was the major radioactive component in the first urine collection, but at later times two more polar compounds predominated. After extensive purification by normal phase-solid phase extraction and reverse-phase high performance liquid chromatography, these compounds were characterized by UV spectroscopy, co-elution with synthetic standards, negative ion electron capture gas chromatography/mass spectrometry, and tandem mass spectrometry. The two major urinary metabolites were structurally determined to be 14-carboxy-hexanor-LTE3 and the conjugated tetraene, 16-carboxy-delta 13-tetranor-LTE4. Three other minor metabolites were detectable in the first urine collection only and were characterized by co-elution with synthetic standards as 16-carboxy-tetranor-LTE3, 18-carboxy-dinor-LTE4, and 20-carboxy-LTE4. omega-Oxidation and subsequent beta-oxidation from the methyl terminus appeared to be the major metabolic fate for sulfidopeptide leukotrienes in man. The accumulation of the 14-COOH-LTE3 and 16-COOH-delta 13-LTE4 may reflect a rate-limiting step in further oxidation of these compounds which places a conjugated triene or conjugated tetraene, respectively, two carbons removed from the CoA ester moiety. Also in the first urine collection there was another minor metabolite identified as N-acetyl-LTE4, however, no subsequent beta-oxidation of this metabolite was observed. The major metabolites of LTE4 might be useful in assessing in vivo production of sulfidopeptide leukotrienes in humans.

Transcellular biosynthesis of sulfidopeptide leukotrienes during receptor-mediated stimulation of human neutrophil/platelet mixtures

The ability of different cell types to cooperate in the metabolism of reactive intermediates of arachidonic acid such as leukotriene A4 (LTA4) is currently receiving considerable attention. Of critical importance is the demonstration that transfer of LTA4 could occur under conditions when relatively low amounts of LTA4 are produced such as would be expected for in vitro receptor-mediated stimulation. Stimulation of human neutrophils with a combination of chemotactic factor (formyl-methionyl-leucyl-phenylalanine, FMLP) and phagocytosable particles (opsonized zymosan) resulted in little production of LTC4 alone, but measurable quantities appeared when platelets were coincubated. When these agonists were added to platelets alone in the absence of neutrophils, no LTC4 was produced. In the presence of stimulated neutrophils, the final synthesis of LTC4 was shown to occur within the platelets (from neutrophil-derived LTA4) by experiments using platelets that had been prelabeled with 35S-cysteine to label intracellular platelet glutathione. Other 35S-labeled sulfidopeptide leukotriene metabolites were also produced in this coincubation of neutrophils and platelets. The observed synergy between FMLP and opsonized zymosan in the production of LTC4 when neutrophils and platelets were coincubated may involve priming the neutrophil for LTA4 production. Activation of platelets or endothelial cells with thrombin did not alter the capacity of either cell to convert exogenously added LTA4 into LTC4. This would support the suggestion that even when platelets are activated they retain their capacity to metabolize LTA4 into LTC4. Finally, previous exposure of the platelets to LTA4 did not affect subsequent metabolism of arachidonic acid by the cyclooxygenase pathway to thromboxane A2 (TXA2) except at very high concentration of LTA4. These results suggest that cell-cell interactions may be critical determinants of the profile of eicosanoids produced in physiologic and pathophysiologic circumstances. In particular, we believe that both endothelial cells and platelets can, together with neutrophils, contribute relatively large amounts of sulfidopeptide leukotrienes to inflammatory and thrombotic events. These cell-cell interactions are aspirin-insensitive; therefore, aspirin-treated platelets are capable of synthesizing the vasoconstrictor LTC4 from neutrophil LTA4 at a time when they can no longer produce thromboxane.

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.

Fast atom bombardment and collision-induced dissociation of prostaglandins and thromboxanes: Some examples of charge remote fragmentation

The mass spectra of products found by collisional activation of selected prostaglandins and thromboxanes were studied by tandem mass spectrometry as barium carboxylate salts and as carboxylate anions. Collision-induced dissociation (CID) of these closed shell ions generated by fast atom bombardment mass spectrometry reveals a wealth of structural information for these hydroxy acids. Decomposition reactions were found to be dependent upon the eicosanoid ring structure and the type of ion being studied, either positive or negative ion. The bariated carboxylate salts undergo reactions by processes that are similar to those previously characterized as charge remote mechanisms in which neutral species are lost as in thermal and photolytic decompositions. The most abundant ion is formed by loss of water from each of the hydroxyl groups present on the prostaglandin or thromboxane structure. For these multifunctionalized eicosanoids, typical patterns of decomposition emerge as characteristic of the oxygen substituents present along the carbon chain of the eicosanoid structure. The structural information obtained from the barium salts along with those from the carboxylate anions is substantially different, yet the structural information from each process is complementary. The CIDs of positive ions (metalated salts) provide structural information concerning the substituents between the carboxyl group and C12 of the eicosanoid structure, whereas the decompositions of the carboxylate anions (negative ion mode) provide data concerning structure alterations of the eicosanoid structure between C15 and C20.

Mediator release after endobronchial antigen challenge in patients with respiratory allergy

The aim of the present study was to evaluate the release of some potential mediators of allergic reactions, such as histamine, peptide leukotrienes (LTs), LTB4 and prostaglandin D2 (PGD2), in bronchoalveolar lavage (BAL) fluids from 11 patients with respiratory allergy (eight with bronchial asthma and three with allergic rhinitis), who underwent specific endobronchial challenge. Histamine, peptide LT, and PGD2 levels in BAL fluids increased significantly after antigen stimulation both in patients with asthma and in patients with rhinitis. By contrast, LTB4 concentration was always below the limits of detection of the radioimmunoassay. In patients with asthma, histamine concentration increased from 5.3 +/- 0.6 ng/ml in lavages obtained before provocation to 20.2 +/- 5.8 ng/ml (mean +/- SEM; p less than 0.04) 5 minutes after bronchoprovocation. Peptide LTs increased from 0.32 +/- 0.08 to 0.82 +/- 0.21 ng/ml (p less than 0.02) and PGD2 from 0.06 +/- 0.01 ng/ml to 0.36 +/- 0.09 ng/ml (p less than 0.02). Elevated histamine, peptide LT, and PGD2 concentrations were also found in the 15-minute postchallenge BAL fluids. Similar results were obtained in patients with rhinitis. Histamine concentration was 3.4 +/- 0.6 ng/ml in prechallenge bronchial lavages and 11.3 +/- 1.7 ng/ml in postchallenge lavages; peptide LTs increased from 0.13 +/- 0.008 ng/ml to 0.73 +/- 0.21 ng/ml, and PGD2 from 0.05 +/- 0.01 ng/ml to 0.26 +/- 0.06 ng/ml.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolism of exogenous leukotrienes by cultured human keratinocytes

Leukotrienes are involved in diseases associated with a neutrophilic infiltrate. The role of human keratinocytes in the metabolism and inactivation of leukotrienes has not been thoroughly examined. We added exogenous radioactive leukotrienes to cultured human keratinocytes and evaluated the metabolic products using high-performance liquid chromatography. Over a 24-h period, unstimulated cultured keratinocytes convert leukotriene B4 to unidentified polar molecules. Leukotriene C4 is converted to a leukotriene D4/leukotriene E4-like product. Cultured human keratinocytes have the ability to metabolize leukotrienes and thus the keratinocyte may play a major role in the in vivo metabolism of leukotrienes produced during inflammatory dermatoses.

Nucleotide sequence and further characterization of the Synechococcus sp. strain PCC 7002 recA gene: complementation of a cyanobacterial recA mutation by the Escherichia coli recA gene

The nucleotide sequence and transcript initiation site of the Synechococcus sp. strain PCC 7002 recA gene have been determined. The deduced amino acid sequence of the RecA protein of this cyanobacterium is 56% identical and 73% similar to the Escherichia coli RecA protein. Northern (RNA) blot analysis indicates that the Synechococcus strain PCC 7002 recA gene is transcribed as a monocistronic transcript 1,200 bases in length. The 5' endpoint of the recA mRNA was mapped by primer extension by using synthetic oligonucleotides of 17 and 27 nucleotides as primers. The nucleotide sequence 5' to the mapped endpoint contained sequence motifs bearing a striking resemblance to the heat shock (sigma 32-specific) promoters of E. coli but did not contain sequences similar to the E. coli SOS operator recognized by the LexA repressor. An insertion mutation introduced into the recA locus of Synechococcus strain PCC 7002 via homologous recombination resulted in the formation of diploids carrying both mutant and wild-type recA alleles. A variety of growth regimens and transformation procedures failed to produce a recA Synechococcus strain PCC 7002 mutant. However, introduction into these diploid cells of the E. coli recA gene in trans on a biphasic shuttle vector resulted in segregation of the cyanobacterial recA alleles, indicating that the E. coli recA gene was able to provide a function required for growth of recA Synechococcus strain PCC 7002 cells. This interpretation is supported by the observation that the E. coli recA gene is maintained in these cells when antibiotic selection for the shuttle vector is removed.

Platelet-activating factor and leukotriene biosynthesis in whole blood. A model for the study of transcellular arachidonate metabolism

As a model to perhaps better indicate potential in vivo tissue inflammatory events, the generation of leukotriene (LT)B4, 20-OH-LTB4, sulfidopeptide LT, and platelet-activating factor (PAF) from human whole blood stimulated with zymosan was compared with that produced by isolated human neutrophils suspended either in buffer or plasma. Several reports have shown that substantial LTB4 biosynthesis could be induced after addition of zymosan to whole blood, but little was known concerning the generation of other important lipid mediators, or the cellular source of these. We have shown that, in spite of some subject variation, the zymosan-induced production of 20-OH-LTB4, LTB4, and LTE4 reached maxima within 30 to 60 min with 1.1, 2.8, and 0.60 ng/10(6) neutrophils, respectively. These concentrations would be sufficient to induce significant biologic effects. Studies with isolated cell mixtures suggested that the neutrophil was the primary source of the lipid mediators or their precursors in this system, although a number of other cell types contributed as accessory cells to the final amounts and mix of mediators produced. The ratio of neutrophils to accessory cells in mixed cell experiments dramatically modified the metabolic pattern of leukotriene generation. The concentration of LTB4 was increased in the presence of RBC and that of LTE4 when platelets were present. These results suggested that cellular cooperation and transcellular biosynthesis played a key role in the overall production of eicosanoids such as LTB4 and LTC4. The concomitant synthesis of PAF in isolated cells and in whole blood was also determined as another member of the complex lipid mediator network. Maximal production of cell-associated PAF was observed within 30 min after the initiation of phagocytosis and reached levels of 3 to 5 ng PAF/10(6) neutrophils. When other cells were present in a coincubation system, the time course for production of PAF was not altered, but maximal concentration of PAF was lower, perhaps as a result of enhanced PAF metabolism. Study of eicosanoids and other lipid mediator production in mixed cell populations provides insight into those events occurring within tissues, where cross-cell signaling and transcellular biosynthesis may occur.

Platelet-activating factor and leukotriene biosynthesis in whole blood. A model for the study of transcellular arachidonate metabolism

As a model to perhaps better indicate potential in vivo tissue inflammatory events, the generation of leukotriene (LT)B4, 20-OH-LTB4, sulfidopeptide LT, and platelet-activating factor (PAF) from human whole blood stimulated with zymosan was compared with that produced by isolated human neutrophils suspended either in buffer or plasma. Several reports have shown that substantial LTB4 biosynthesis could be induced after addition of zymosan to whole blood, but little was known concerning the generation of other important lipid mediators, or the cellular source of these. We have shown that, in spite of some subject variation, the zymosan-induced production of 20-OH-LTB4, LTB4, and LTE4 reached maxima within 30 to 60 min with 1.1, 2.8, and 0.60 ng/10(6) neutrophils, respectively. These concentrations would be sufficient to induce significant biologic effects. Studies with isolated cell mixtures suggested that the neutrophil was the primary source of the lipid mediators or their precursors in this system, although a number of other cell types contributed as accessory cells to the final amounts and mix of mediators produced. The ratio of neutrophils to accessory cells in mixed cell experiments dramatically modified the metabolic pattern of leukotriene generation. The concentration of LTB4 was increased in the presence of RBC and that of LTE4 when platelets were present. These results suggested that cellular cooperation and transcellular biosynthesis played a key role in the overall production of eicosanoids such as LTB4 and LTC4. The concomitant synthesis of PAF in isolated cells and in whole blood was also determined as another member of the complex lipid mediator network. Maximal production of cell-associated PAF was observed within 30 min after the initiation of phagocytosis and reached levels of 3 to 5 ng PAF/10(6) neutrophils. When other cells were present in a coincubation system, the time course for production of PAF was not altered, but maximal concentration of PAF was lower, perhaps as a result of enhanced PAF metabolism. Study of eicosanoids and other lipid mediator production in mixed cell populations provides insight into those events occurring within tissues, where cross-cell signaling and transcellular biosynthesis may occur.

Leukotrienes C4 and D4 as potent mitogens for cultured human neonatal melanocytes

Arachidonic acid and its metabolites (eicosanoids) are membrane-derived inflammatory mediators with a diverse set of biologic properties affecting numerous cells and organ systems, including the skin. They have been implicated in the pathogenesis of inflammatory skin disease and post-inflammatory hyperpigmentation. We have studied the ability of arachidonic acid, prostaglandin D2, prostaglandin E2, leukotriene B4, leukotriene C4, leukotriene D4, and leukotriene E4 to enhance the growth of cultured human melanocytes. Of these compounds, only leukotriene C4 and leukotriene D4 were capable of stimulating melanocyte proliferation. In addition, cultured melanocytes metabolized leukotriene C4 to leukotriene E4 with greater than 60% conversion in less than three hours. Melanocytes grown on suboptimal media (doubling time 12-20 days) respond in a dose-dependent fashion to leukotriene C4, with a significant difference from control noted at 28 days with a concentration of LTC4 of 30 nM and a doubling time of 5-8 days. We feel that leukotriene C4 and D4 could play an important role in post-inflammatory melanocyte hyperplasia.

Transcellular sulfidopeptide leukotriene biosynthetic capacity of vascular cells

Cells in the vasculature, including polymorphonuclear leukocytes, platelets, and endothelial cells, have been shown to be jointly involved in the biosynthesis of active lipid mediators derived from arachidonic acid. Stimulation of neutrophils with the calcium ionophore A23187 as a model for cell activation results in production of leukotriene (LT)A4 with subsequent intracellular conversion into LTB4. When platelets or endothelial cells were present in the incubation system, LTC4 was produced from the neutrophil-derived LTA4. Whereas production and release of LTA4 under resting conditions in vivo might be expected to be quite low, under pathologic conditions, LTA4 production could be markedly increased. Therefore, the metabolism of exogenous LTA4 by platelets and endothelial cells was studied at a wide range of LTA4 concentrations. The production of LTC4 during coincubation of neutrophils with platelets was found to be dependent on neutrophil number ranging from 2 x 10(5) to 2 x 10(7) cells/mL. When a fixed number of neutrophils were stimulated with platelets alone or with mixtures of platelets and endothelial cells, LTC4 production was observed to be dependent on both acceptor cell types. These results suggest that mixed cell populations, which are likely to occur in vivo, may be critical determinants of the profile of eicosanoids produced in pathophysiologic circumstances. We suggest that both endothelial cells and platelets, in the presence of neutrophils, contribute large quantities of sulfidopeptide leukotrienes to inflammatory and thrombotic situations. Furthermore, platelets, because of their quantity and reactivity, may play a pivotal role in transcellular biosynthesis of eicosanoids.