Recovery of nasal prostaglandin production after inhibition by aspirin

We have investigated the duration of the inhibitory effects of aspirin in eight healthy volunteers after oral administration of a single 500 mg dose. Prostaglandin E2, D2 and leukotriene C4 levels in nasal lavage fluid were measured by radioimmunoassay without purification by high performance liquid chromatography. The inhibitory effects of aspirin on eicosanoid synthesis were maximum between 1 h to 24 h, showing total recovery within 3-5 days. LTC4 synthesis was not modified by aspirin.

A calcium-independent 5-lipoxygenase system in mast/basophil PT-18 cells

Mammalian 5-lipoxygenase systems exist in inactive or cryptic states and have to be stimulated in order to metabolize exogenous [14C]arachidonic acid to 5-HETE and leukotrienes. In most cells, both the activation process and the 5-lipoxygenase activity are calcium-dependent. However, the cryptic 5-lipoxygenase system in the murine PT-18 mast/basophil cell line, which can be stimulated by 15-hydroxyeicosatetraenoic acid (15-HETE), is unusual. Studies with fura-2 loaded PT-18 cells indicate that increases in cytosolic calcium do not appear to correlate with enhanced 5-lipoxygenase product formation. Thus, both the calcium ionophore ionomycin and arachidonic acid increase cytosolic calcium levels but have very little effect on [14C]5-HETE formation, whereas 15-HETE induces large increases in [14C]5-HETE production but no concomitant enhancement in cytosolic calcium is observed. Chelation of extracellular calcium by 3 mM EGTA resulted in a 30-40% inhibition of [14C]5-HETE formation induced by 15 HETE, whereas 3 mM EGTA has no appreciable effect on a crude PT-18 5-lipoxygenase homogenate. These results indicate that in PT-18 cells, calcium does not appear to play an important role in either the 15-HETE-induced activation process, or the enzymatic activity of the cryptic 5-lipoxygenase system.

Transformation of arachidonic acid by 5- and 15-lipoxygenase pathways in bovine adrenal fasciculata cells

[1-14C]Arachidonic acid was incubated with isolated bovine adrenal fasciculata cells for 15 min at 37gC. The metabolites were separated and purified by reverse- and straight-phase high performance liquid chromatography, and identified by gas chromatography-mass spectrometry or radioimmunoassay. Identified metabolites were 5-hydroxy-6,8,11,14-eicosatetraenoic acid (5-HETE), 15-hydroxy-5,8,11,13-eicosatetraenoic acid (15-HETE), leukotriene B4 and 11,14,15-trihydroxy-5,8,12-eicosatrienoic acid (11,14,15-THET). Addition of 15-hydroperoxy-5,8,11,13-eicosatetraenoic acid (15-HPETE), an intermediate metabolite of 15-lipoxygenase pathway to microsomes of bovine adrenal fasciculata cells resulted in the formation of 11,14,15-THET. The formation of 11,14,15-THET by microsomes was not dependent on the presence of NADPH, while it was dose-dependently suppressed by ketoconazole, a potent inhibitor of cytochrome P-450 dependent enzymes. These results indicate that 5- and 15-lipoxygenase pathways of arachidonic acid may exist in bovine adrenal fasciculata cells and that 15-HPETE is further metabolized to 11,14,15-THET by adrenal microsomal cytochrome P-450.

The 15-lipoxygenase product, 8R,15S-diHETE, stereospecifically sensitizes C-fiber mechanoheat nociceptors in hairy skin of rat

1. This study examined the effects of the 15-lipoxygenase product of arachidonic acid metabolism, (8R,15S)-dihydroxyicosa-(5E-9,11,13Z)tetraenoic acid (8R,15S-diHETE), on mechanical thresholds and thermal responses of saphenous nerve cutaneous C-fiber nociceptors that innervate the hairy skin of the rat hindpaw. Single C-fiber mechanoheat nociceptors (C-MH) that had von Frey hair (VFH) thresholds greater than 5 g and were activated by a noxious heat stimulus were chosen for study. We also studied the effects of prostaglandin E2 (PGE2), a cyclooxygenase product of arachidonic acid metabolism, on these nociceptors. 2. The 63 C-MHs studied had a conduction velocity of 0.82 +/- 0.03 m/s (mean +/- SE) and a mechanical threshold of 13.4 +/- 2.4 g. In a subgroup of these (n = 24), the thermal threshold was measured as (44 +/- 1 degree C) (mean +/- SE). 3. 8R,15S-diHETE produced a significant decrease in mechanical threshold of C-MHs (n = 33). The 8R,15S-diHETE-induced sensitization of C-MHs to mechanical stimuli was completely antagonized by coadministration with a stereoisomer, 8S,15S-diHETE (n = 10). 4. The mechanical threshold of C-MHs (n = 10), previously injected with the combination of 8R,15S-diHETE and 8S,15S-diHETE, was significantly reduced by a subsequent injection of PGE2. In a separate group of C-MHs (n = 7), PGE2 was co-injected with 8S,15S-diHETE, which failed to antagonize the sensitizing effect of PGE2 on mechanical threshold. 5. 8R,15S-diHETE also sensitized C-MHs (n = 9) to a thermal stimulus consisting of 37 degrees C for 5 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Endothelin-1 stimulates arachidonate 15-lipoxygenase activity and oxygen radical formation in the rat distal lung

We investigated the effects of intravenous bolus of endothelin-1 on the metabolism of eicosanoids and oxygen radicals in the distal lung unit of the rat. Intravenous bolus of endothelin-1 caused a significant increase in 15-hydroxyeicosatetraenoic acid of bronchoalveolar lavage fluid and oxygen radicals produced by the bronchoalveolar cells. Endothelin-1 exhibited a stimulatory effect on the 15-lipoxygenase activity in the lung homogenate. Thus, endothelin-1 may contribute to the inflammatory and hyperreactive process of lungs, by enhancing the release of 15-hydroxyeicosatetraenoic acid and oxygen radicals in the distal lung unit.

Effect of dietary oils on the production of n-3 and n-6 metabolites of leukocyte 5-lipoxygenase in five rat strains

We examined the influence of various dietary oils, including linseed and fish oil on the relative rates of leukotriene B4 (LTB4) and LTB5 production by rat peritoneal exudate cells in five rat strains. While there was an association between the membrane phospholipid levels of the fatty acid precursors (arachidonic acid (AA) and eicosapentaenoic acid (EPA)) and the rate of synthesis of their respective 5-lipoxygenase products (LTB4 and LTB5), the rate of LTB4 synthesis was a combined function of both AA and EPA levels. We observed a strong linear relationship (correlation coefficient = 0.99) between the ratio of EPA/AA in the cell membrane phospholipids and the ratio of LTB5/LTB4 produced by these cells in vitro; this association was independent of genetic (strain) variability and was independent of the source of EPA (dietary EPA or EPA endogenously synthesized from dietary alpha-linolenic acid).

Auranofin stimulates LTA hydrolase and inhibits 5-lipoxygenase/LTA synthase activity of isolated human neutrophils

The effect of auranofin on the 5-lipoxygenase pathway was studied in human neutrophils stimulated with either fMLP or A23187 (with or without arachidonic acid). The synthesis of leukotriene B4 (LTB4), 5-HETE and the all-trans isomers of LTB4 was measured by HPLC. At low concentrations (0.5-2.0 microM), auranofin stimulated LTB4 synthesis, but inhibited it at higher concentrations (100% inhibition at less than 10 microM). In contrast auranofin caused dose-dependent inhibition of the synthesis of 5-HETE and the all-trans isomers of LTB4. Similar observations were made with each agonist. The stimulation of LTB4 synthesis and inhibition of the trans isomer production suggests that auranofin at low concentrations stimulates LTA hydrolase--the enzyme that converts LTA4 to LTB4, whereas the inhibition of synthesis of all lipoxygenase products at higher auranofin concentrations, suggests inhibition of 5-lipoxygenase/LTA synthase.

Evidence for 5-lipoxygenase activity in human B cell lines. A possible role for arachidonic acid metabolites during B cell signal transduction

Ligand binding to B lymphocytes via membrane Ig initiates a cascade of events beginning with the hydrolysis of phosphatidylinositol 4,5-bisphosphate into diacylglycerol and inositol 1,4,5-trisphosphate. Subsequent to the activation of protein kinase C and the induction of a rise in intracellular calcium by diacylglycerol and inositol 1,4,5-trisphosphate, there is gene transcription and eventually cellular activation. By mimicking the initial event of B cell activation with phorbol ester and calcium ionophore one can begin to identify the many mediators used in signaling between the membrane and the nucleus. We have examined the effect of calcium on arachidonic acid (AA) metabolism in several EBV-transformed human B cell lines. The cells were labelled with [3H]AA and stimulated with the calcium ionophore A23187. Analysis of the supernatant by reversed-phase HPLC demonstrated a dose-dependent release of an AA metabolite that coeluted with authentic 5-hydroxyeicosatetraenoic acid (5-HETE). In addition, the AA metabolite coeluted with standard 5-HETE under straight-phase chromatography. Further analysis by RIA confirmed the identification of 5-HETE and revealed an additional metabolite, 5-HETE lactone (5-HL). 5-HL is the intramolecular ester of 5-HETE generated in the presence of acid. We were unable to convert [3H] 5-HETE into 5-HL during sample preparation unless cells were present, suggesting that the 5-HL, is of cellular origin. These results suggest that the AA metabolites 5-HETE and its intramolecular ester 5-HL may play a role in B cell activation because they are produced subsequent to a rise in intracellular Ca2+, an event that occurs during cross-linking of membrane Ig.

Leukotriene C4 is an essential 5-lipoxygenase intermediate in A23187-induced macrophage cytostatic activity against P815 tumor cells

Resident peritoneal macrophages incubated with 3.5 x 10(-7) M Calcium ionophore A23187 in tumor cell growth medium (TGM) release large amounts of leukotriene (LT)E4 and an unidentified 5-lipoxygenase product, whereas A23187-stimulated macrophages produce in serum free medium LTD4, predominately. LTC4 and 3H-LTC4 incubated for 20 min at 37 degree C in serum containing TGM, convert into LTE4 and 3H-LTE4, respectively. Thus, LTC4 released from A23187-stimulated macrophages is an intermediate in TGM which rapidly converts into LTE4, probably because of the presence of gamma-glutamyl transpeptidase and cystenylglycinase in TGM. Macrophages express antitumor cytostatic activity towards P815 cells (49-53%) in a cocultured ratio (macrophage: tumor cell) 2:1 when stimulated with 3.5 x 10(-7) M A23187 in TGM. The 5-lipoxygenase inhibitor AA861 reverses the cytostatic activity by 42-58% and it inhibits also the formation of A23187-induced 5-lipoxygenase products from macrophages. Restoration of 38% macrophage- antitumor cytostatic activity by exogenous LTC4 (10(-8) M) indicates that LTC4 is an essential 5-lipoxygenase intermediate in the pathway of required signals underlying A23187-induced macrophage antitumor cytostatic activity. Macrophages not stimulated by A23187 do not express cytostatic activity in the presence of LTC4. This implies that besides LTC4, increased cytosolic [Ca2+] is required for A23187 induction of macrophage cytostatic activity.

Role of lipoxygenase in the mechanism of acrosome reaction in mammalian spermatozoa

The acrosome reaction (AR) in bull spermatozoa was induced by the Ca2(+)-ionophore A23187, by dilauroylphosphatidylcholine or by arachidonic acid in the presence of Ca2+ in the incubation medium. The occurrence of AR was determined by following the release of acrosin from the cells. Nordihydroguaiaretic acid (NDGA), an inhibitor of both lipoxygenase and prostaglandin-synthetase, caused 35%, 43% and 69% inhibition of AR at concentrations of 1, 10 or 100 microM, respectively. Eicosatetraynoic acid (ETYA), an analogue of arachidonic acid, caused 17%, 61% and 77% inhibition of AR at concentrations of 20, 40 or 80 micrograms/ml, respectively. When AR was induced by arachidonic acid, ETYA, causes 36% and 58% inhibition at concentrations of 2 or 20 micrograms/ml, respectively. Under identical conditions, 100 microM indomethacin, a specific inhibitor of prostaglandin-synthetase, showed no inhibition but rather 35% stimulation at acrosin release rate. The fact that AR is inhibited by NDGA and not by indomethacin indicates that the lipoxygenase, rather than prostaglandin-synthetase, is involved in the mechanism of AR. Since the inhibition by NDGA is seen in the presence of the Ca-ionophore, we suggest that lipoxygenase activity is not involved in enhancing calcium transport into the cell, but rather at other steps in AR mechanism. A thin-layer chromatography revealed the presence of 15-HETE, the classical product of 15-lipoxygenase activity, which was identified by HPLC. Under AR conditions, there is an elevation of lipoxygenase products and the addition of NDGA caused a reduction in their levels. The inhibition of acrosin release by NDGA can be eliminated by adding 15-HETE or 15-HPETE to the incubation medium. In conclusion, we suggest here for the first time, a physiological role for 15-lipoxygenase in the mechanism of AR in mammalian spermatozoa.

Regulatory role of arachidonic acid-derived metabolites for proliferation of transformed murine Leydig cell in serum-free culture condition

The growth-regulatory ability of eicosanoids from arachidonic acid is poorly understood. To investigate their role in cell growth, we cultured transformed murine Leydig cells (B-1 or B-1 F) in serum-free medium supplemented with various compounds modulating arachidonic acid metabolism. The addition of 5-lipoxygenase inhibitors (AA 861, NDGA and quercetin) showed a growth-stimulative effect. On the other hand, their growth was remarkably inhibited by arachidonic acid added into the culture medium. This growth-inhibiting ability of arachidonic acid was almost completely reversed by a simultaneous exposure of B-1 cells to lipoxygenase inhibitor. Exogenously added 5-HETE inhibited cell proliferation in a dose-dependent manner. These results suggest that 5-lipoxygenase-catalyzed products from arachidonic acid have the ability to suppress the proliferation of some transformed cells.

A glycerol ether induces mobilization and 12-lipoxygenation of arachidonic acid in macrophages. Synergistic effect on mobilization and induction of leukotriene C formation by activators of protein kinase C

A glycerol triether, 1,2-isopropylidene 3-0-decanyl-sn-glycerol, was found to induce mobilization of arachidonic acid from ethanolamine phosphoglycerides and phosphatidylinositol in mouse peritoneal macrophages. This effect showed structural specificity, occurred without activation of protein kinase C and resulted in formation and release of predominantly 12-hydroxy-eicosatetraenoic acid. Activators of kinase C (4-beta-phorbol 12-myristate 13-acetate and 1,2-dioctanoyl-sn-glycerol) instead specifically enhance prostaglandin E2 formation. When macrophages were exposed to both a kinase C activator and the glycerol triether, the mobilization of arachidonic acid was synergistically enhanced and formation of leukotriene C was induced.

Exogenous action of 5-lipoxygenase by its metabolites on luteinizing hormone release in rat pituitary cells

The stimulatory effect of exogenously administered potato 5-lipoxygenase (0.1-0.3 U/2 ml) on luteinizing hormone (LH) release was demonstrated in rat anterior pituitary cells in a superfusion system. Nordihydroguaiaretic acid (NDGA), an inhibitor of 5-lipoxygenase, abolished the effect of the enzyme on LH secretion. The secretory effect on LH after 5-lipoxygenase administration was biphasic and dependent on Ca2+ indicating that 5-lipoxygenase affects LH release through its oxygenation reaction. Another series of experiments demonstrated that activation of 5-lipoxygenase, expressed as production of leukotriene (LT) B4 and C4 (728 +/- 127 pg/10(6) cells and 178 +/- 23 pg/10(6) cells, respectively) occurs in rat pituitary cells after addition of Ca2+ ionophore A23187. However, LTB4 and LTC4 were not formed by pituitary cells that had previously been desensitized by gonadotropin-releasing hormone (GnRH), the physiological ligand of LH release. These results are consistent with a role of 5-lipoxygenase metabolites in the mechanism of GnRH-induced LH secretion.

Evidence for cytokine regulation of cholesterol metabolism in herpesvirus-infected arterial cells by the lipoxygenase pathway

Cytokines such as tumor necrosis factor (TNF), interleukin-1 (IL-1), and gamma-interferon (IF) are produced by activated hematopoietic cells. They possess antiviral activity and have other biological activities such as induction of cell proliferation and hemorrhagic necrosis of tumors. Since herpes simplex virus (HSV) infection of human vascular cells is known to produce a biochemical and cytopathological effect virtually indistinguishable from atherosclerosis, we hypothesized that these cytokines many prevent cholesteryl ester (CE) accumulation in arterial smooth muscle cells (SMC) that is seen with herpesvirus infection. We now report that TNF and IL-1 but not gamma-IF prevent CE accumulation in HSV-infected arterial SMC by induction of cyclic AMP-dependent CE hydrolysis. This effect is mediated through the arachidonate 12-lipoxygenase pathway via 12-HETE since pretreatment of cells with several lipoxygenase inhibitors abolishes the antiviral effect and 12-HETE is the major (greater than 99%) lipoxygenase metabolite produced by these cells. This conclusion is further based on our observations that TNF and IL-1 enhance 12-HETE production in SMC and that 12-HETE significantly increases both intracellular cyclic AMP and lysosomal CE hydrolysis. Moreover, dibutyryl cyclic AMP restored a normal phenotype in these virally infected cells. Collectively, these findings identify for the first time a biochemical mechanism involved in the reduction of lipid accumulation in virally infected arterial SMC by these potent cytokines.

5-Hydroxyeicosanoids selectively stimulate the human neutrophil 15-lipoxygenase to use endogenous substrate

When human neutrophils, prelabeled with [3H]arachidonic acid, were incubated with 5S,15S-dihydroxyeicosatetraenoic acid (5,15-diHETE), a dose-dependent increase in the 15-lipoxygenase product [3H]-15-HETE was observed relative to untreated cells. Typically, a fivefold increase in [3H]-15-HETE formation was obtained upon exposure of these cells to 3 muM 5,15-diHETE. There was no appreciable enhancement of the 5-lipoxygenase metabolite [3H]-5-HETE. Product identities were confirmed by comparing retention times on straight- and reversed-phase HPLC with authentic standards, and RIA. Other 5-hydroxyeicosanoids, such as 5-HETE, 5-HETE methyl ester, and leukotriene B4(5S,12R-diHETE), were equally effective in stimulating the formation of [3H]-15-HETE, but exogenously added lipoxin A4, lipoxin B4, 15-HETE, and 12-HETE were much less potent, whereas stearic acid was ineffective. The diHETEs also showed a greater selectivity in activating the 15-lipoxygenase relative to the 5-lipoxygenase. A likely source of substrate for the 15- and 5-lipoxygenases is a pool of cell-associated but noncovalently bound arachidonic acid. In [3H]arachidonic acid-prelabeled neutrophils, the amount of free [3H]arachidonic acid ranged between 50 and 700 fmol/10(7) cells, whereas unlabeled neutrophils contained 100-2,200 pmol/10(7) cells of nonesterified arachidonic acid. The exogenously added hydroxyeicosanoids induce a 0.5-3% conversion of this substrate pool to product. These findings indicate that the 15-lipoxygenase in human neutrophils is a cryptic enzyme that needs to be stimulated in order to metabolize endogenous substrate. It is possible that 5-hydroxyeicosanoids may mimic an as yet unidentified physiological activator of the 15-lipoxygenase.

Identification of a novel arachidonate 12-lipoxygenase in bovine tracheal epithelial cells distinct from leukocyte and platelet forms of the enzyme

We examined the characteristics of an arachidonate 12-lipoxygenase in bovine tracheal epithelial cells in relation to the enzyme expressed in leukocytes and platelets. Homogenous preparations of intact or disrupted tracheal epithelial cells metabolized arachidonic acid predominantly to (12S)-hydroxyeicosatetraenoic acid, and subcellular fractionation by differential centrifugation demonstrated that the 12-lipoxygenase activity was localized predominantly to the 100,000 x g supernatant (cytosol fraction). Analysis of cytosolic enzymatic activity for pH dependence (maximum activity at pH 7.4-8.0), divalent cation effects (no dependence on cations), and kinetic characteristics (lag phase elimination by addition of hydroperoxide) exhibited similarity to leukocyte and platelet 12-lipoxygenases. Immunoprecipitation experiments demonstrated that the epithelial 12-lipoxygenase reacted with a monoclonal antibody (lox-2) directed against leukocyte 12-lipoxygenase but not with an antibody (HPLO-3) against the platelet enzyme. Immunoaffinity chromatography of the epithelial 100,000 x g supernatant fraction using lox-2 linked to Affi-Prep 10 yielded a single predominant protein band (Mr = 72,000) by sodium dodecyl sulfate-polyacrylamide gel electrophoresis identical in apparent mass to the bovine leukocyte lipoxygenase. Western blotting using a polyclonal antibody to leukocyte 12-lipoxygenase showed peroxidase staining of the same 72-kDa protein band. Activity assays of the purified enzymes demonstrated that substrate specificity for the epithelial 12-lipoxygenase was similar to that of the leukocyte enzyme, but the epithelial enzyme more efficiently converted 18-carbon fatty acids to the corresponding monohydroxylated conjugated dienes. We conclude that bovine tracheal epithelial cells express a 12-lipoxygenase that has immunological reactivity similar to leukocyte and distinct from platelet 12-lipoxygenase and possesses substrate specificity distinct from both enzymes. We further suggest that lipoxygenase heterogeneity may provide a basis for different functional roles for the enzyme in different cell types.

MK886, a potent and specific leukotriene biosynthesis inhibitor blocks and reverses the membrane association of 5-lipoxygenase in ionophore-challenged leukocytes

Recently, we have shown that ionophore activation of human leukocytes results in leukotriene synthesis and a translocation of 5-lipoxygenase from the cytosol to cellular membrane. This membrane translocation was postulated to be an important early activation step for the enzyme. 3-[1-(p-Chlorobenzyl)-5-(isopropyl)-3-tert-butylthioindol-2-yl]-2, 2- dimethylpropanoic acid (MK886) is a potent and specific inhibitor of leukotriene biosynthesis in vivo and in intact cells, but has no direct effect on 5-lipoxygenase activity in cell-free systems. In this report, we show that MK886 can both prevent and reverse the membrane translocation of 5-lipoxygenase, in conjunction with the inhibition of leukotriene synthesis. Similar compounds of the indole class could also inhibit the membrane translocation of 5-lipoxygenase in a rank order of potency that correlated with their potencies for leukotriene synthesis inhibition. In contrast L-656,224, a direct 5-lipoxygenase inhibitor, had no effect on the translocation of the enzyme. Attempts to demonstrate the effects of MK886 on the association of 5-lipoxygenase with membrane in cell-free preparations failed due to a nonspecific Ca2+-dependent sedimentation of the enzyme. The mechanism of action of MK-886 is therefore to block translocation, prevent subsequent activation of 5-lipoxygenase, and hence block cellular leukotriene biosynthesis.

Requirement of a 5-lipoxygenase-activating protein for leukotriene synthesis

Leukotrienes, the biologically active metabolites of arachidonic acid, have been implicated in a variety of inflammatory responses, including asthma, arthritis and psoriasis. Recently a compound, MK-886, has been described that blocks the synthesis of leukotrienes in intact activated leukocytes, but has little or no effect on enzymes involved in leukotriene synthesis, including 5-lipoxygenase, in cell-free systems. A membrane protein with a high affinity for MK-886 and possibly representing the cellular target for MK-886 has been isolated from rat and human leukocytes. Here, we report the isolation of a complementary DNA clone encoding the MK-886-binding protein. We also demonstrate that the expression of both the MK-886-binding protein and 5-lipoxygenase is necessary for leukotriene synthesis in intact cells. Because the MK-886-binding protein seems to play a part in activating this enzyme in cells, it is termed the five-lipoxygenase activating protein (FLAP).

Formation of 12-lipoxygenase metabolites in rat cerebral cortical slices: stimulation by calcium ionophore, glutamate and N-methyl-D-aspartate

The 12-lipoxygenase pathway of arachidonic acid metabolism in rat cerebral cortex slices is stimulated by exogenous arachidonic acid, Ca2+ ionophore A23187, phorbol ester, glutamate, N-methyl-D-aspartate (NMDA) but not by kainate and other neurotransmitters except norepinephrine. The 12-hydroxyeicosatetraenoic acid formed is the (S)-enantiomer. A specific role for 12-lipoxygenase metabolites in NMDA receptor activation and long term potentiation is proposed.

Influence of hypoxia on 5-lipoxygenase pathway in rat alveolar macrophages

The effect of hypoxia was studied on the ionophore A23187-induced leukotriene production by rat alveolar macrophages. The production of LTB4 and LTC4 decreased with reducing oxygenation without change of cell viability. The synthesis of 5-HETE increased during hypoxia and the total production of LTB4, LTC4 and 5-HETE, the major metabolites of the 5-lipoxygenase pathway in rat alveolar macrophages, was equal during normoxia and hypoxia. Arachidonate release and LTA4-converting into LTB4 and LTC4 was unaffected by hypoxia. LTB4- and LTC4-degradating activities were not affected by hypoxia. These results suggest that LTA4 synthase reaction of leukotrienes biosynthesis might be suppressed by hypoxia.

Dietary supplementation with oils rich in (n-3) and (n-6) fatty acids influences in vivo levels of epidermal lipoxygenase products in guinea pigs

Certain dietary oils may have therapeutic potential in the treatment of inflammatory skin disorders. Presumably, the fatty acid constituents of these dietary oils exert their effects by altering the levels of cutaneous eicosanoids. Prompted by this possibility, we investigated whether supplementation of guinea pig diets with fish oil [rich in 20:5(n-3)] or borage oil [rich in 18:3(n-6)] could significantly alter epidermal levels of eicosanoids compared with control animals supplemented with olive oil. After feeding periods of 4, 8 or 12 wk, the epidermis from the animals was analyzed for: 1) fatty acid composition of individual epidermal phospholipids, 2) levels of lipoxygenase products, and 3) levels of cyclooxygenase products (prostaglandins). Our results demonstrated that the animals supplemented with dietary fish oil had elevated levels of 20:5(n-3) in epidermal phospholipids and elevated epidermal levels of 15-hydroxyeicosapentaenoic acid (15-HEPE) [the 15-lipoxygenase product of 20:5(n-3)] compared with guinea pigs fed olive oil or borage oil. Similarly, the animals supplemented with dietary borage oil had elevated levels of 20:3(n-6) [the epidermal elongase product of 18:3(n-6)] in epidermal phospholipids and elevated epidermal levels of 15-hydroxyeicosatrienoic acid [15-HETrE, the epidermal 15-lipoxygenase product of 20:3(n-6)] compared with guinea pigs fed olive oil or fish body oil. There were no significant changes in epidermal levels of prostaglandins. Both 15-HEPE and 15-HETrE have been identified as possible anti-inflammatory metabolites, and their elevated presence in the epidermis of animals fed oils rich in 20:5(n-3) or 18:3(n-6) may provide a mechanism for the beneficial effects of these oils on inflammatory conditions.

Heterogeneity of human mast cells and basophils. Effects of a putative 5-lipoxygenase inhibitor

The effects of a putatively specific 5-lipoxygenase inhibitor, 2(12-hydroxydodeca-5,10-dinyl)-3,5,6-trimethyl-1,4-benzoquin one (AA-861), and its major metabolite, M-I, were assessed using anti-IgE activated human basophils, lung mast cells and skin mast cells. In basophils and lung mast cells, no effects on histamine release were observed, whereas leukotriene C4 (LTC4) production was inhibited (IC50 values less than 1 microM). In addition, prostaglandin D2 (PGD2) production was inhibited in lung mast cells (IC50 congruent to 5 microM). In contrast, in skin mast cells both histamine release and PGD2 production were reduced by AA-861 and M-I, with IC50 values of congruent to 5 and 0.4 microM for histamine and PGD2, respectively. These data reveal biochemical heterogeneity among human histamine-containing cells and underscore the necessity of assessing a pharmacologic agonist in relevant cell systems.