Total profiling by GC/NICIMS of the major cyclo-oxygenase products from antigen and leukotriene-challenged guinea-pig lung

Bioactive Compounds from Marine Sponges and Algae: Effects on Cancer Cell Metabolome and Chemical Structures

Metabolomics represent the set of small organic molecules generally called metabolites, which are located within cells, tissues or organisms. This new “omic” technology, together with other similar technologies (genomics, transcriptomics and proteomics) is becoming a widely used tool in cancer research, aiming at the understanding of global biology systems in their physiologic or altered conditions. Cancer is among the most alarming human diseases and it causes a considerable number of deaths each year. Cancer research is one of the most important fields in life sciences. In fact, several scientific advances have been made in recent years, aiming to illuminate the metabolism of cancer cells, which is different from that of healthy cells, as suggested by Otto Warburg in the 1950s. Studies on sponges and algae revealed that these organisms are the main sources of the marine bioactive compounds involved in drug discovery for cancer treatment and prevention. In this review, we analyzed these two promising groups of marine organisms to focus on new metabolomics approaches for the study of metabolic changes in cancer cell lines treated with chemical extracts from sponges and algae, and for the classification of the chemical structures of bioactive compounds that may potentially prove useful for specific biotechnological applications.

Revisiting the usefulness of thromboxane-A2 modulation in the treatment of bronchoconstriction in asthma

Airway smooth muscle (ASM) is the effector cell in the bronchoconstrictory pathway. It is believed that the bronchoconstriction present in asthma is associated with changes in the airway milieu that affect ASM excitation-contraction coupling and Ca(2+)-handling. Asthmatics also react differently to ventilatory mechanical strain. Deep inspiration (DI), which produces bronchodilation in healthy individuals, is less effective in asthmatics, and even enhances bronchoconstriction in moderate to severely affected patients. Our laboratory has previously studied the mechanotransductory pathway of airway stretch-activated contractions (Rstretch) leading to DI-induced bronchoconstriction. We demonstrated the ability of agonists acting through thromboxane A2 (TxA2) receptors to amplify airway Rstretch responses. Despite the involvement of excitatory prostanoids in bronchoconstriction, clinical trials on treatments targeting TxA2-synthase inhibition and TP-receptor antagonism have produced mixed results. Studies in Western populations produced mostly negative results, whereas studies performed in Asian populations showed mostly positive outcomes. In this review, we discuss the role of TxA2-synthase inhibition and TP-receptor antagonism in the treatment of asthmatics. We present information regarding variations in study designs and the possible role of TP-receptor gene polymorphisms in previous study outcome discrepancies. Perhaps future studies should focus on asthmatic patients with DI-induced bronchoconstriction in particular, planting the seed for the individualized treatments for asthmatics.

New strategies to identify molecular markers predicting chemotherapy activity and toxicity in breast cancer

Despite significant improvements in the treatment and outcomes of early-stage breast cancer, the quest continues to find biological and molecular markers that would enable earlier diagnosis or better prediction of treatment efficacy and toxicity. Metabolomics--the latest and one of the most exciting of the 'omic' sciences--has shown early promise as a non-invasive diagnostic aid in ovarian cancer, and may allow the detection of subtle metabolic changes that could have diagnostic, prognostic or predictive value in breast cancer. Routine monitoring of circulating tumour cells (CTCs) has also been advocated as a novel means of detecting breast cancer progression earlier, and identifying alterations in tumour cells that might signal the need for therapy changes. Ongoing studies should help to answer important questions relating to the use of metabolomics and CTC evaluation as new strategies to monitor cancer progression and identify markers of chemotherapy activity and toxicity.

Metabolomics reviewed: a new "omics" platform technology for systems biology and implications for natural products research

Metabolomics is the study of global metabolite profiles in a system (cell, tissue, or organism) under a given set of conditions. The analysis of the metabolome is particularly challenging due to the diverse chemical nature of metabolites. Metabolites are the result of the interaction of the system's genome with its environment and are not merely the end product of gene expression but also form part of the regulatory system in an integrated manner. Metabolomics has its roots in early metabolite profiling studies but is now a rapidly expanding area of scientific research in its own right. Metabolomics (or metabonomics) has been labeled one of the new "omics", joining genomics, transcriptomics, and proteomics as a science employed toward the understanding of global systems biology. Metabolomics is fast becoming one of the platform sciences of the "omics", with the majority of the papers in this field having been published only in the last two years. In this review metabolomic methodologies are discussed briefly followed by a more detailed review of the use of metabolomics in integrated applications where metabolomics information has been combined with other "omic" data sets (proteomics, transcriptomics) to enable greater understanding of a biological system. The potential of metabolomics for natural product drug discovery and functional food analysis, primarily as incorporated into broader "omic" data sets, is discussed.

Anaphylaxis increases 8-iso-prostaglandin F2alpha release from guinea-pig lung in vitro

8-Iso-prostaglandin F2alpha, release from isolated and perfused guinea-pig lung was measured by radioimmunoassay. 8-Iso-prostaglandin F2alpha release was detectable under basal conditions and increased 10-fold during antigen-induced bronchoconstriction, concomitant with the increase of thromboxane B2 and prostaglandin E2. The anti-8-iso-prostaglandin F2alpha serum used in the radioimmunoassay seems to be quite specific for this compound. Pretreatment of lungs with indomethacin (a non-selective inhibitor of cyclooxygenase) reduced 8-iso-prostaglandin F2alpha release under basal conditions and completely abolished the increase observed during lung anaphylaxis. Pretreatment of lungs with NS 398 (N-[2-cyclohexyl]-4-nitrophenyl methanesulphonamide), a selective inhibitor of cyclooxygenase-2, did not change basal or antigen-induced 8-iso-prostaglandin F2alpha release at all. We conclude that under basal conditions guinea-pig lung perfusates contain low levels of 8-iso-prostaglandin F2alpha-like immunoreactivity, which increase 10-fold during antigen-induced bronchoconstriction. This isoprostane seems to be derived from the cyclooxygenation of arachidonic acid via the constitutive form of cyclooxygenase.

Bradykinin-evoked sensitization of neuropeptide release from afferent neurons in the guinea-pig lung

1. It has been shown that bradykinin (BK) causes sensitization of airway sensory neurons and an enhancement of the cough reflex in guinea-pigs. In the present study, the guinea-pig isolated perfused lung was used to investigate the possible enhancement by BK of histamine-evoked neuropeptide release from peripheral terminals of primary afferent neurons, and to determine the contribution of cyclooxygenase products of arachidonate metabolism to this effect. 2. The lung was perfused with oxygenated physiological salt solution containing peptidase inhibitors (thiorphan, bestatin and captopril, 1 microM each). BK and histamine were added to the perfusate for 10 and 5 min, respectively. 3. BK alone (0.1 microM) evoked the release of 10.35+/-2.4 fmol immunoreactive calcitonin gene-related peptide (CGRP), histamine alone (100 microM) evoked the release of 12.7+/-1.6 fmol CGRP. Stimulation with 100 microM histamine in the presence of 0.1 microM BK (added 5 min before histamine and present during histamine) evoked the release of 67.1+/-5.3 fmol CGRP. 4. Prostaglandin (PG) release was stimulated by BK (418+/-71 pmol 15-keto-13,14-dihydro-PGF2alpha and 345+/-59 pmol 6-keto-PGF1alpha), and, to a lesser extent, by histamine (36.1+/-7.4 pmol 15-keto-13,14-dihydro-PGF2alpha, and 24.6+/-3.9 pmol 6-keto-PGF1alpha). Prostaglandin release induced by histamine in the presence of BK was not significantly higher than with BK alone. 5. Indomethacin (5 microM) as well as the bradykinin B2 receptor antagonist HOE140 (icatibant, 1 microM) inhibited prostaglandin release following stimulation with histamine in combination with BK. CGRP release evoked by histamine in combination with BK was attenuated by indomethacin and HOE140 to 22.1+/-7.8 fmol and 16.4+/-3.8 fmol, respectively, significantly less than the value obtained in control experiments (67.1+/-5.3 fmol). 6. The results suggest that BK-induced stimulation of prostaglandin synthesis results in facilitation of histamine-evoked release of pro-inflammatory neuropeptides from afferent neurons, a mechanism that probably becomes relevant during inflammation, and that can be blocked by a bradykinin B2 receptor antagonist.

Pulmonary pharmacology of DT-TX 30 SE, a potent selective combined thromboxane synthetase inhibitor and receptor antagonist, in guinea pigs

A novel chemical compound, DT-TX 30 SE (E-6-(4-2-(4-chlorobenzenesulphonylamino)-ethyl)phenyl)-6-(3-pyrid yl)- hex-5-enoic acid), was studied in various models of guinea pig pulmonary function. The compound was a potent inhibitor (ED50 0.019 mg/kg, i.v.) of bronchospasm induced by the thromboxane receptor agonist U-46619, indicating thromboxane receptor antagonism. At even lower doses (ED50 0.0036 mg/kg, i.v.), it blocked arachidonic acid-induced bronchospasm. Interpretation of the latter results as evidence for additional thromboxane synthetase inhibitory activity was supported by the inhibition of arachidonic acid- or bradykinin-induced thromboxane B2 production in an isolated lung preparation, although prostaglandin E2 and prostaglandin 6-oxo-F(1 alpha) production measured at the same time were not inhibited. The potency of DT-TX 30 SE was compared with thromboxane receptor antagonists and synthetase inhibitors described in the literature. As a receptor antagonist, DT-TX 30 SE was significantly more potent than BM 13505 and BM 13177 (assessed by antagonism of U-46619-induced bronchospasm), but less potent than SQ 29548, while as a thromboxane synthetase inhibitor, it was significantly more potent than OKY 046 and UK 37248 as assessed by antagonism of arachidonic acid-induced bronchospasm or (OKY 046) inhibition of thromboxane production in isolated lung. The compound was active by the oral route as shown by its ability, at 10 mg/kg, p.o., to significantly reduce the immediate allergic response of sensitized guinea pigs to an ovalbumin aerosol.

Arachidonic acid metabolism in alveolar macrophages from actively sensitized guinea-pigs: effects of sensitization and specific allergen

Arachidonic acid (AA) metabolism, including mediator release and lipid turnover, was explored in [3H]AA-radiolabelled alveolar macrophages obtained from guinea-pigs actively sensitized to ovalbumin (sAM) and controls (cAM). The basal and allergen-induced AA metabolism of cAM and sAM were examined in the presence and absence of homologous serum obtained from the same control or sensitized animals. Basal AA metabolism of cAM and sAM involved the release of lipoxygenase and cyclooxygenase [3H]metabolites and free [3H]AA into the culture medium. However, in sAM, the production of free [3H]AA was significantly lower than in cAM. The allergen had no effect on the basal AA metabolism of cAM and sAM or on the metabolism of cAM and sAM cultured in the presence of control serum. In contrast, it increased the [3H]LTC4-D4 and free [3H]AA production of sAM cultured with sensitized serum but not those of cAM cultured with the same sensitized serum. In sAM, the allergen effect disappeared when the sensitized serum was heated for 1 h to 56 degrees C. Our results suggest that two factors, both induced by the active sensitization of guinea-pigs, one in the serum and one on the macrophages obtained from sensitized guinea-pigs, are required for the allergen to have an impact on the AA metabolism of alveolar macrophages in increasing the production of 5-lipoxygenase metabolites.

Effects of vasoactive intestinal polypeptide on antigen-induced bronchoconstriction and thromboxane release in guinea-pig lung

1. Exogenous vasoactive intestinal polypeptide (VIP) infused into the pulmonary artery of isolated and ventilated lungs of guinea-pigs decreased, in a dose-dependent fashion (1.0-10.0 nmol), airway resistance and thromboxane B2 (TXB2, the stable hydrolysis product of TXA2) release in the perfusion medium. Prostacyclin (PGI2) synthesis, as reflected by the release of its stable hydrolysis product 6-oxo-PGF1 alpha, was unaffected. Pretreatment with the 5-lipoxygenase inhibitor BWA4c (3.5 x 10(-5) M) did not modify the bronchodilatory effect of VIP or its inhibitory action on TXB2 release. 2. Basal release of immunoreactive VIP from perfused lungs decreased from an initial value of 0.96 +/- 0.10 ng min-1 (mean +/- s.e.mean) in the first 2 min to an average of 0.58 +/- 0.10 ng min-1 in the following 15-20 min. 3. Antigen challenge with ovalbumin (0.1%) in sensitized lungs caused an anaphylactic reaction in 45% of tested lungs, concomitant with a 5 fold increase in both VIP and TXB2 release. Tetrodotoxin pretreatment (10(-6) M) reduced basal VIP release by > 80% and abolished the VIP increase observed during anaphylaxis, without modifying TXB2 release or the bronchoconstrictor response. 4. Indomethacin (10(-6) M) inhibited TXB2 synthesis and release by > 90%, delayed the bronchoconstrictor response and blunted the increased VIP release during lung anaphylaxis, without influencing basal VIP release. 5. The 5-lipoxygenase inhibitor BWA4c (3.5 x 10(-5) M) blunted the increase of TXB2 and VIP release from guinea-pig lung and attenuated the bronchoconstrictor response following ovalbumin challenge. 6. The administration of exogenous VIP as a continuous infusion (10-8 M) attenuated the bronchoconstriction and the release of cyclo-oxygenase metabolites following antigen challenge.7. Acetylcholine (10-6-l0-5 M) infused into the pulmonary artery induced a dose-dependent bronchoconstriction not associated with enhanced VIP or TXB2 release.8. The TXA2 mimetic U-46619 (0.1-1.0 nmol) caused dose-dependent increases in airway resistance,concomitant with an up to 10 fold increase in VIP release. VIP inhibited arachidonate-induced in vitro aggregation of washed rabbit platelets in a dose-dependent manner over a dose range 10-8 10-6 M.Despite the antiaggregatory effect of VIP, TXB2 and PGE2 synthesis was reduced only to a minor extent,and there was no redirection of arachidonate metabolism from TXA2 to PGE2, indicating that VIP does not act as a TX synthase inhibitor in vitro.9. We conclude that VIP may play a role in regulating bronchial smooth muscle reactivity in lung anaphylaxis by inhibiting the synthesis and release of TXA2, a potent vasoactive and bronchoconstrictor agent. TXA2, on the other hand, strongly enhances neuronal VIP release.

Leukotriene D4 receptors are not negatively coupled to adenylyl cyclase in guinea-pig lung parenchyma

1. The possibility that receptors for the peptide-containing leukotrienes may be negatively coupled to adenylyl cyclase in guinea-pig lung parenchyma was investigated by comparing the effect of leukotriene D4 (LTD4) on the intracellular cyclic nucleotide (cyclic AMP and cyclic GMP) content and on the activity of cyclic AMP-dependent protein kinase (PKA). In addition, the potential association between changes in the cyclic nucleotide content and the ability of LTD4 to increase lung parenchymal tone was also evaluated. 2. Non-cumulative challenge of parenchymal lung strips with LTD4 elicited concentration-dependent contractions (pD2 = 8.23) that were paralleled by concentration-related increases in the intracellular level of cyclic AMP and cyclic GMP, and in the activation state of PKA (Kact = 33 nM). Temporally, these biochemical effects of LTD4 were transient, peaking after approximately 5 min drug contact thereafter decaying, despite the continued generation of tone. Both the biochemical and mechanical effects of LTD4 were antagonized by the LTD4-receptor blocking drug, ICI 198,615 (1 microM for 60 min), indicating that they were receptor-mediated events. 3. Challenge of guinea-pig lung with LTD4 (200 nM; EC100 for tension generation) stimulated a 150 and 70 fold increase in the elaboration of thromboxane B2 (TXB2) and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) respectively, relative to that generated spontaneously. 4. Pretreatment of lung strips for 60 min with an irreversible inhibitor of cyclo-oxygenase, flurbiprofen,at a concentration (8 microM) that abolished both basal and LTD4 (200 nM)-induced TXB2 and 6-keto-PGF1alpha release, relaxed rapidly the spontaneous tone of the tissues, reduced the cyclic AMP content by ~50%and lowered the PKA activity ratio from 29% to 17%. In addition, flurbiprofen abolished the ability of LTD4 (200 nM) to increase the cyclic AMP content and to activate PKA. Functionally, the magnitude of LTD4 (200 nM)-induced tone and the increase in cyclic GMP content were attenuated by approximately 20% and 50% respectively in flurbiprofen-treated tissues.5. In flurbiprofen-treated tissues, isoprenaline (10 microM for 10 min) increased the cyclic AMP content(from 4 to 27 pmol mg-1 protein) and activated PKA (from 15% to 26%). Preincubation (30 s or 5 min)of lung with LTD4 (200 nM) did not inhibit (or enhance) these isoprenaline-induced effects.6. Pretreatment of lung strips for 60 min with the thromboxane synthetase inhibitor, dazmegrel (10 microM),relaxed the spontaneous tone of the tissues, abolished the LTD4 (200 nM)-stimulated release of TXB2 and significantly enhanced (~two fold) the elaboration of 6-keto-PGF1alpha. In addition, dazmegrel attenuated (by ~50%) LTD4 (200 nM)-induced cyclic GMP accumulation but approximately doubled both the cyclic AMP content and PKA activity ratio. LTD4-induced contractions, in contrast, were not affected by dazmegrel.7. EP 092 (1 microM for 60 min), a selective TP-receptor blocking drug, had no effect on spontaneous tone,eicosanoid formation or on the cyclic GMP content of guinea-pig lung parenchymal strips. Likewise,EP 092 exerted no significant mechancial effect in lung challenged with LTD4 (200 nM) although it did potentiate, to a small extent, the ability of LTD4 (200 nM) to increase the cyclic AMP content.8. It is concluded that LTD4 can increase the intracellular level of cyclic AMP in guinea-pig parenchyma and activate PKA by a leukotriene-receptor-mediated mechanism sensitive to ICI 198,615. However,these biochemical actions of LTD4 are induced indirectly by an arachidonic acid-derived cyclo-oxygenase product(s) other than TXA2. Thus, contrary to reports of other investigators, no evidence was found to corroborate the finding that stimulation of leukotriene receptors on guinea-pig lung parenchyma results in a rapid lowering of the cyclic AMP content even in cyclo-oxygenase-blocked tissues. These data,therefore, do not support the hypothesis that leukotriene-induced tension generation is dependent upon a prior reduction in the cyclic AMP content.

Pharmacologic modulation of antigen-induced pulmonary responses in the perfused guinea pig lung

The effect of various enzyme inhibitors and receptor antagonists on antigen (ovalbumin)-induced changes in pulmonary hemodynamics (arterial pressure, capillary pressure, and arterial and venous resistance), fluid filtration, and airway reactivity were monitored for 60 min in recirculating Ringer's-perfused, actively sensitized lungs. Bolus ovalbumin (30 micrograms) injection into the pulmonary artery produced initial (3 min postovalbumin) increases in pulmonary arterial pressure of 68 +/- 9% above baseline, which were followed by secondary increases (143 +/- 45% above baseline) at 30 min postovalbumin. Ovalbumin challenge also caused initial increases in pulmonary capillary pressure, arterial resistance, and venous resistance within 3 min after administration (100 +/- 34%, 51 +/- 10%, and 221 +/- 77% above baseline, respectively), which were further elevated at the end of the 60-min experimental period (292 +/- 74%, 66 +/- 29%, and 559 +/- 61% above baseline, respectively). Ovalbumin-induced increases in intratracheal pressure (771 +/- 142% above baseline) peaked at 3 min postchallenge and gradually returned towards baseline. Ovalbumin-induced changes in lung weight increased gradually over the perfusion period (3.5 +/- 1.0 g above baseline at 60 min postovalbumin). Antigen-induced changes in pulmonary arterial pressure, intratracheal pressure, and lung weight were abolished by pretreatment with the histamine1-receptor antagonist, pyrilamine (1 microM). The cyclooxygenase inhibitor, indomethacin (1 microM), potentiated antigen-induced secondary increases in pulmonary arterial pressure, intratracheal pressure, and lung weight.(ABSTRACT TRUNCATED AT 250 WORDS)

Inflammatory mediators and cellular infiltration of the lungs in a guinea pig model of the late asthmatic reaction

Alterations in cell numbers, vascular permeability, and concentrations of various inflammatory mediators in the lung were measured in a guinea pig model of the late asthmatic reaction. Animals sensitized by inhalation of ovalbumin were challenged with an aerosol of ovalbumin or saline, and bronchoalveolar lavage fluid (BALF) and peripheral blood were collected after periods ranging from 5 min to 72 h. Increased vascular leakage within the lungs was indicated by elevated BALF/plasma albumin ratios at all time points, and was maximal 6 h after challenge. There were increased numbers of eosinophils in BALF by 6 h after challenge and they remained elevated at least until 72 h. A corresponding increase in the proportion of blood leukocytes represented by eosinophils was observed at 6 and 17 h, which suggests that these cells may be drawn to the lung following their release into the circulation, but by 72 h the proportion in blood had returned to normal. A transitory neutrophilia was evident in BALF and blood 6 h after allergen exposure, but there were no allergen-induced changes in BALF numbers of macrophages, lymphocytes, epithelial cells, or mast cells (as assessed by concentrations of cell-associated histamine). beta-Glucuronidase activity was significantly increased in BALF of guinea pigs at 2 h and 17 h following challenge. The degree to which eicosanoids can be recovered in BALF was investigated by instilling a range of tritiated compounds into the lungs of normal guinea pigs at the time of lavage. Ratio high-performance liquid chromatography revealed that there had been little metabolism of the eicosanoids recovered in BALF. However, there was evidence for a rapid removal of these mediators from the lung, a process which will militate against their accurate quantitation in BALF. Histamine, prostaglandin D2, and thromboxane B2 were detected in BALF but did not differ between treatment groups, and levels showed no simple relationship with the other inflammatory changes measured.

The metabolism of prostaglandin D2. Evidence for the sequential conversion by NADPH and NAD+ dependent pathways

Cell-free 100,000 g supernatants from human lung converted PGD2 into a product which on HPLC was indistinguishable from 9 alpha, 11 beta-PGF2. The rate of reaction was relatively slow (0.30 +/- 0.03 pmol/min/mg protein). In the presence of NAD+, 9 alpha, 11 beta-PGF2 was itself metabolized at a rate of 1.46 +/- 0.3 pmol/min/mg protein. The product of this reaction was less polar than the substrate and eluted with an HPLC retention time similar to that seen in our previous study where it was identified by GC/MS as being 15-keto-9 alpha, 11 beta-PGF2. There was no evidence for the formation of 13,14-dihydro-15-keto-9 alpha, 11 beta-PGF2. The sequence of metabolism of PGD2 was further established in cell-free supernatants prepared from guinea-pig liver and kidney which have previously been shown to be rich in both 11-ketoreductase and 15-hydroxy-prostaglandin dehydrogenase (PGDH) activities. Reactions contained both NAD+ and a NADPH-regenerating system and demonstrated the sequential metabolism of PGD2 to 9 alpha, 11 beta-PGF2 and ultimately 13,14-dihydro-15-keto-9 alpha, 11 beta-PGF2. Under these conditions the rate of the C-15 oxidation reaction was slower than that of 11-ketoreduction. These observations provide further support for our previous suggestions that the 11-ketoreduction of PGD2 is followed by a PGDH-type reaction, and that these reactions are likely to occur sequentially in vivo provided that the appropriate cofactors are present.

Inhibitors of prostaglandin dehydrogenase (Ph CL 28A and Ph CK 61A) increase output of prostaglandins from rat isolated lung

1 Two potent inhibitors of prostaglandin dehydrogenase (PGDH), Ph CL 28A and Ph CK 61A, have been investigated for their effects on prostaglandin catabolism and synthesis in rat isolated lung. 2 Both CL 28A (0.3 microM) and CK 61A (0.5 and 5 microM) markedly increased the survival of prostaglandin E2 (PGE2) and PGF2 alpha on a single passage through the pulmonary circulation. 3 Both inhibitors delayed the efflux of 14C following injection of [14C]-PGE2 through the pulmonary circulation. 4 Output of PGE2 and PGF2 alpha but not that of 6-oxo-PGF1 alpha from exogenous arachidonic acid (AA) was increased by CL 28A. 5 Output of all three prostaglandins from endogenous AA stimulated by calcium ionophore A23187 was increased by CL 28A. 6 With CK 61A, output of 6-oxo-PGF1 alpha from exogenous AA was not increased but that from endogenous AA was increased by either concentration of this inhibitor. 7 We conclude that it is possible to increase output of biologically active prostaglandins from lung by preventing their inactivation in situ. 8 The apparent selectivity of PGI2 synthesis from endogenous AA to potentiation by the inhibitors may have therapeutic possibilities.

Modulation of the contractile activity of the guinea-pig lung parenchymal strip by exogenous 5,8,11,14,17-eicosapentaenoic acid

Exogenous eicosapentaenoic acid (EPA, 16.5 mumol/l or 33 mumol/l) inhibited dose-dependently the anaphylactic contractile response of guinea-pig lung parenchymal strips suspended in an organ bath. As determined by radioimmunoassay, EPA inhibited in a dose-dependent manner the anaphylactic release of the cyclooxygenase products thromboxane (TX) B2 and 6-keto-prostaglandin (PG) F1 alpha but simultaneously enhanced the release of sulfidopeptide (SP)-leukotrienes (LT). Indomethacin (2.8 mumol/l) abolished the release of cyclooxygenase products but potentiated the release of SP-LT. However, indomethacin treatment did not affect the inhibitory action of EPA on the contractile response of the anaphylactic lung strips. The lipoxygenase inhibitor, esculetin (50 mumol/l), inhibited the release of SP-LT and also that of cyclooxygenase products of polyunsaturated fatty acid metabolism. The combination of esculetin and EPA resulted in enhanced inhibition of the anaphylactic contractile response as compared to EPA alone. By reversed phase high pressure liquid chromatography (HPLC), SP-LT from anaphylactic lung parenchymal strips was shown to consist of LTD4 and LTE4. EPA-pretreated lung strips released upon immunologic challenge additional immunoreactivity comigrating with authentic LTC4, LTC5, LTD5 and LTE5. While anaphylactic control strips also released LTB4, in the bath fluid of EPA-treated strips, an additional immunoreactive compound migrating with the retention time of LTB5 was observed. In non-sensitized guinea-pig lung parenchymal strips EPA inhibited the myotropic activity of exogenous mediators such as histamine (9 mumol/l), LTC4 (16 nmol/l) and the TX mimetic U 46619 (28.4 nmol/l), an effect which was neither affected by indomethacin (2.8 mumol/l) nor by the lipoxygenase inhibitor nordihydroguaiaretic acid (NDGA, 10 mumol/l).(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibitory effects of a novel platelet activating factor (PAF) antagonist (BN 52021) on antigen-induced prostaglandin and thromboxane formation by the guinea pig lung

The effects of a new Platelet-Activating Factor (PAF-acether) antagonist (BN 52021) extracted from Ginkgo biloba leaves have been studied on the release of metabolites of arachidonic acid in IgG-dependent guinea pig pulmonary anaphylaxis in vitro. Prostaglandin E2 (PGE2) and thromboxane B2 (TxB2) were assayed using a novel ELISA technique. The release of PGE2 and TxB2 from anaphylactic lungs reached a maximum 4-5 min following the antigen challenge (about 3.2 and 31.0 ng/ml respectively) and decayed slowly during the following 25 min. BN 52021 (1, 3 and 30 micrograms/ml) produced dose-dependent decreases of the release of PGE2 and TxB2. These results suggest that there are some interactions between the release of icosanoids and PAF-acether in anaphylaxis.

Release of leukotrienes into the perfusate of calcium-ionophore stimulated rabbit lungs. Influence of 5-lipoxygenase inhibitors

Arachidonic acid and the calcium ionophore A23187 are known to provoke a pulmonary artery pressor response, edema formation and release of thromboxane B2 (TxB2) and 6-keto prostaglandin-F1 alpha (6-keto PGFl alpha) into the recirculating perfusion fluid of isolated blood-free perfused rabbit lungs. Here we investigated the release of leukotrienes (LTs) by repetitive 0.1 microM A23187 challenge in the presence or absence of cyclooxygenase and 5-lipoxygenase inhibitors. RP-HPLC analysis of perfusion fluid extracts persistently showed peaks with retention times of authentic LTC4, -D4, -E4 and -B4. Fractionated RP-HPLC eluate subjected to radioimmunoassay (RIA) with LTC4 and LTB4 antibodies showed two major peaks of immunoreactivity corresponding to those compounds and minor immunoreactivity with LTD4 and LTE4 in accordance with the stated cross-reactivities of the LTC4 antibody. Good correlation for both LTB4 and LTC4 levels measured by RP-HPLC versus RIA of collected HPLC peaks was found. Five to ten min after A23187 challenge, LTC4, -D4 and -B4 levels ranged from 800 to 1600 pg/ml perfusate. LTC4 reached a maximum level at 20 min whereas LTB4 slightly increased over a 35 min period. Upon repeated A23187 challenge, interrupted by rinsing phases with fresh perfusion fluid, the LT release was reproducible several times with increasing reaction strength. This performed in presence of increasing concentration of the 5-lipoxygenase inhibitors AA-861 or U-60,257 caused a dose-dependent inhibition of the release of all LTs with an IC50 of approximately 10(-8) to 10(-7) M and 10(-6) M, respectively. Cyclooxygenase inhibition with acetylsalicylic acid at doses completely suppressing the A23187 induced pressor response did not inhibit the peptidoleukotriene release and only slightly depressed LTB4 release.

CONCLUSION

using a rapid and sensitive extraction and RP-HPLC method isolated lungs are found to release nanomolar amounts of LTs into the perfusate upon repetitive A23187 challenge, suppressed by 5-lipoxygenase inhibition.

Influence of the thromboxane antagonist BM 13.177 on the arachidonic acid-induced increase in pulmonary vascular resistance and permeability in rabbit lungs

In blood-free perfused isolated rabbit lungs increased availability of free arachidonic acid (AA), whether exogenously applied or released from the endogenous membrane phospholipid pool after different stimuli, causes an acute pulmonary artery pressor response and an increase in vascular permeability. Previous experiments suggested that the vasoconstriction is caused primarily by the cyclooxygenase product thromboxane (Tx) A2, whereas an increase in the capillary filtration coefficient must be ascribed to non-cyclooxygenase products of AA. The influence of BM 13.177, a non-prostanoic antagonist of TxA2- and endoperoxide-effects in platelets, on the AA-induced vascular effects in isolated rabbit lungs was investigated. BM 13.177 dose-dependently inhibited the pressor responses evoked by repetitive direct application of AA (IC50 approximately 10(-6) M) or by repetitive stimulation of endogenous AA-release with the calcium-ionophore A 23187 (IC50 approximately 10(-7) M), with maximum reduction of the pressor responses to less than 15%. The generation of TxA2 and of prostaglandin (PG) I2 evoked by these stimuli was, however, not altered. At a concentration of 10(-5) M BM 13.177 did not influence the capillary filtration coefficient, measured during venous pressure challenge, under baseline conditions and after stimulation with AA in presence of indomethacin.

CONCLUSION

BM 13.177 acts as TxA2/endoperoxide antagonist with dose-dependent inhibition of AA-induced vasoconstriction in the pulmonary vascular bed.

Qualitative and quantitative measurement of hydroxy fatty acids, thromboxanes and prostaglandins using stable isotope dilutions and detection by gas chromatography-mass spectrometry

Methods for measurement of the metabolites of arachidonic acid (AA), namely prostaglandins (PGs), thromboxanes (TXs) and hydroxy fatty acids, using stable isotope dilution gas chromatography--mass spectrometry are described. With a few exceptions, labelled species of the various AA metabolites are not commercially available and were therefore synthesized in our laboratory. [2H8]AA, produced by deuteration of eicosatetraynoic acid, was used for comparing the metabolism of exogenously added and endogenously present AA in fibroblast cultures. After derivatization and catalytic hydrogenation, structure elucidation and quantification of the different hydroxy fatty acids was carried out by determination of the fragment ions resulting from alpha-cleavage at the site of the hydroxy function. During catalytic hydrogenation a significant hydrogen--deuterium exchange was observed. To eliminate this problem, 18O-labelled standards were prepared by exchanging the oxygen of the carboxylic acid group. The preparation and the use of hydroxy fatty acids, PGs and TXs labelled with 18O is described.

Differential release of eicosanoids by bradykinin, arachidonic acid and calcium ionophore A23187 in guinea-pig isolated perfused lung

The effects of infusions of bradykinin (0.2 microM), calcium ionophore A23187 (0.5 microM) and arachidonic acid (13 microM) on the release of eicosanoids from the guinea-pig isolated perfused lung were investigated using radioimmunoassay for thromboxane B2 (TXB2), 6-oxo-prostaglandin F1 alpha (6-oxo-PGF1 alpha), PGE2, leukotriene B4 (LTB4) and LTC4 and bioassay using the superfusion cascade. Bradykinin released more 6-oxo-PGF1 alpha than TXB2, whereas arachidonic acid and ionophore released more TXB2 than 6-oxo-PGF1 alpha. The time course of eicosanoid release varied with the stimulus: bradykinin and arachidonic acid produced an immediate release, whereas the ionophore showed a slower onset of release. Although the amounts of LTB4 and LTC4 released by the ionophore were very low according to radioimmunoassays, there was evidence from the bioassay of release of a leukotriene-like substance, thought to be LTD4. The leukotriene antagonist FPL 55712 lacks specificity in the guinea-pig trachea; at the concentration used (2 microM) it antagonized contractions of the tracheal strip to PGE2 as well as to LTC4. Our results show that in the guinea-pig perfused lung the metabolism of exogenous arachidonic acid is both qualitatively and quantitatively different from the metabolism of endogenous arachidonic acid; furthermore, the profile of eicosanoid production is stimulus-dependent.

Pulmonary synthesis, release, and metabolism of prostaglandins

Immunologic or calcium-dependent activation of proteolytically dispersed human lung cells containing 5% mast cells causes the release of large amounts of PGD2 and TxB2. In cell purification experiments, only those fractions containing mast cells had the capacity to generate PGD2 and release histamine with IgE-dependent activation. The cells of origin of T X B2 are likely to be cells of the monocyte-macrophage series, although additional eicosanoid release may occur from immunologically activated lymphocytes and eosinophils. In men who have asthma, inhalation of low concentrations of PGD2 results in bronchoconstriction, whereas higher concentrations of PGD2 are needed to produce bronchoconstriction in normal subjects. Subjects with asthma exhibited 3.5-fold greater responsiveness to inhaled PGD2 than to PGF2 alpha. These observations demonstrate that PGD2 is the most potent bronchoconstrictor prostanoid tested in man. In both normal subjects and subjects with asthma, a single inhalation of PGF2 alpha resulted in a doubling in plasma levels of 13,14-dihydro-15-keto-PGF2 alpha. Plasma levels of this metabolite did not change after PGD2 inhalation. These results indicate that the 11-keto reduction of PGD2 to PGF2 alpha with subsequent inactivation is not important in the initial metabolism of PGD2.

Effect of pulmonary oedema induced by alpha-naphthylthiourea on synthesis of cyclo-oxygenase products in rat isolated lungs

Synthesis of COP (prostaglandins; PG and thromboxanes; Tx) from exogenous and endogenous arachidonic acid (AA) was studied in isolated perfused lungs from rats treated in vivo with a single dose of alpha-naphthylthiourea (ANTU; 10mg/kg;). Lung dry:wet weight ratios showed changes characteristic of oedema between 6 and 16h after ANTU. Bioassay of COP showed that COP synthesis from exogenous AA was raised above control values in lungs from rats treated with ANTU, reaching a maximum at 16h after treatment. By radioimmunoassay, the major increase was in 6-oxo-PGF1 alpha, with lesser effects on PGE2 and PGF2 alpha levels. Synthesis of bioassayable COP from endogenous AA induced by the calcium ionophore A23187 was increased as early as 2h after ANTU treatment and remained elevated up to 70h. In lungs 28h after ANTU, 6-oxo-PGF1 alpha release was greater than in normal lungs. These results show that in this model of pulmonary oedema, the potential for COP synthesis was increased. From the time course of this effect, increased COP synthesis was probably a response to the initial damage rather than a cause of the oedema.