Inhibitors Of Arachidonic Acid Cascade Research Articles

The influence of non-steroidal anti-inflammatory drugs with different mechanisms of action on the course of stress reaction, the functional state of kidneys, liver, and heart on the model of acute general cooling

Inhibitors of the arachidonic acid cascade have significant potential as the agents for the prevention of severe cold injuries. The results of the previous studies have demonstrated the pronounced frigoprotective properties of certain non-steroidal anti-inflammatory drugs, primarily diclofenac sodium, etoricoxib, darbufelone mesylate, under the conditions of acute general cooling.
 The aim of the study: to investigate the effect of non-steroidal anti-inflammatory drugs with various mechanisms of action on the course of the stress reaction, the functional state of the kidneys, liver, and heart using the model of acute general cooling.
 Materials and Methods: The experiment was carried out using 35 outbreed male rats weighing 256±5 g. The studied drugs were administered intragastrically 30 minutes before cold injury modelling: diclofenac sodium at a dose of 7 mg/kg, etoricoxib at a dose of 5 mg/kg, darbufelone mesylate at a dose of 20 mg/kg. Acute general cooling was induced by exposure at –18 °C for 2 hours. The efficacy of the studied drugs was evaluated by the values as follows: the body temperature (measured rectally), the course of a stress reaction according to the criteria of “the stress triad”, the functional state of the kidney and liver according to the changes in the blood serum biochemical parameters, the functional state of the heart according to the electrocardiogram.
 Results: It was found that etoricoxib and darbufelone mesylate, and especially diclofenac sodium, demonstrate frigoprotective properties, reducing the severity of hypothermia, have stress-protective activity and a beneficial effect on the functional state of the kidneys. All investigated non-steroidal anti-inflammatory drugs prevent a decrease in myocardial contractility (by the effect on the systolic index) and lengthening of the QT interval caused by acute cold injury. Diclofenac sodium, unlike etoricoxib and darbufelone mesylate, does not enhance the effect of acute general cooling on intraventricular conduction. Under acute exposure to cold, no significant changes in the functional state of the liver were observed, including the groups receiving the nonsteroidal anti-inflammatory medicines.
 Conclusions: The prophylactic administration of the arachidonic acid cascade inhibitors, especially the non-selective COX-2 inhibitor diclofenac sodium, reduces the severity of the stress response, contributes to the maintenance of the renal and cardiac function. There are no significant changes in the functional state of the liver under conditions of the experiment

Effect of arachidonic acid cascade inhibitors on body temperature and cognitive functions in rats in the Morris water maze after acute cold injury.

Objective: The aim of the study was to evaluate the effect of arachidonic acid cascade inhibitors on body temperature and cognitive functions of rats (spatial memory, learning ability) in the Morris water maze test (MWM) after acute cold injury (CI). Methods: Animals were trained to find an escape platform in the MWM for two consecutive days. On the third day, rats were treated with saline (10 ml/kg), diclofenac sodium (7 mg/kg), etoricoxib (5 mg/kg), darbufelone mesylate (20 mg/kg) or montelukast (1 mg/kg) intragastrically (i.g.), 30 minutes before CI modeling. Air hypothermia with an acute general cooling (AGC) model was used as a kind of CI. Animals were subjected to cooling for 2 hours at -18°C. Body temperature was measured before and after CI modeling. MWM experimental trials tests were carried out after cold exposure. Number of successful trials, escape latency, distance moved, velocity, meander, and behavioral patterns in individual quadrants were recorded. Results: In the control pathology group, a statistically significantly body temperature decrease was observed (p<0.05 compared to the initial value). All of the studied drugs reduced hypothermia severity, but only in the sodium diclofenac group this reduction reached a significant level in comparison with the untreated animals (p<0.01). A tendency to reduce the severity of hypothermia was observed in the group of animals treated by etoricoxib, darbufelone mesylate, and montelukast. In the control pathology group, the number of successful trials was significantly decreased (p<0.01), velocity (p<0.05), and escape latency (p<0.05) were increased compared with intact animals. Diclofenac sodium significantly reduced escape latency (p<0.05) and increased the number of successful trials in comparison with the control pathology group (p<0.01). Montelukast tended to improve, etoricoxib and darbufelone mesylate did not improve cognitive functions of rats with CI. Conclusions: The results experimentally substantiate the possibility of effective pharmacoprophylaxis of CI and its negative effects on cognitive functions while applying arachidonic acid cascade inhibitors, particularly the non-selective COX inhibitor diclofenac sodium.

Скринінг низки інгібіторів каскаду арахідонової кислоти на фригопротекторні властивості

Холодові травми (ХТ) донедавна були в основному проблемою військових, однак останнім часом збільшується кількість постраждалих серед цивільного населення. Це пов’язано зі зростаючою популярністю активного способу життя та таких його елементів, як спортивний туризм, альпінізм, катання на лижах, і збільшенням кількості безхатченків. Взимку число постраждалих сягає 12 000. Більшість хворих потребують стаціонарного лікування, смертність перевищує 10 %. За патогенезом ХТ схожа з запаленням, що розвивається за опіків та ішемічних уражень. Значну роль у патогенезі відіграють продукти метаболізму арахідонової кислоти: тромбоксан, простагландини, лейкотрієни. Враховуючи роль ейкозаноїдів у механізмі розвитку ХТ, можна зробити припущення щодо позитивного впливу інгібіторів метаболізму арахідонової кислоти на перебіг цієї патології. Мета дослідження – порівняти виразність фригопротекторного ефекту низки нестероїдних протизапальних препаратів (НПЗП) з різною селективністю й аналгетика-антипіретика парацетамолу на моделі гострого загального охолодження (ГЗО) у мишей. Дослідження виконано на білих мишах самцях масою 20–24 г протягом одного дня з 12.00 до 18.00 год. Для моделювання ГЗО мишей вміщували до індивідуальних пластикових кліток об’ємом 500 см3 без обмеження рухової активності та доступу повітря, розташовували в морозильній камері «Nord Inter-300» з прозорою кришкою за температури –18 °С. Інтегральним показником фригопротекторної дії обрано час життя тварин. Використано такі препарати та субстанції: неселективні інгібітори ЦОГ – ацетилсаліцилова кислота (Аспірин, таблетки, «Bayer», Німеччина), диклофенак натрію (Вольтарен, таблетки, «Novartis», Швейцарія); високоселективні інгібітори ЦОГ-2 – целекоксиб (Целебрекс, таблетки, «Pfizer», США), еторикоксиб (Аркоксія, таблетки, «Merck Sharp &amp; Dohme Idea Inc», США); подвійні інгібітори ЦОГ-2/5-ЛОГ – дарбуфелон, дарбуфелону мезилат, 5-(3,5-ди-трет-бутил-4-гідроксибензиліден)-2(тіазол-2-іліміно)-тіазолідин-4-он (субстанції); інгібітор ЦОГ-3 – парацетамол (Панадол, таблетки, «Glaxo Smith Kline plc», Ірландія). Результати дослідження демонструють, що парацетамол не має фригопротекторних властивостей. Еторикоксиб виявляє найбільший фригопротекторний ефект серед класичних НПЗП. Дарбуфелону мезилат демонструє найвищу фригопротекторну активність серед усіх досліджених препаратів. Враховуючи цей факт, можна припустити важливу роль 5-ЛОГ і лейкотрієнів у патогенезі холодової травми.

α-Conotoxins Enhance both the In Vivo Suppression of Ehrlich carcinoma Growth and In Vitro Reduction in Cell Viability Elicited by Cyclooxygenase and Lipoxygenase Inhibitors.

Several biochemical mechanisms, including the arachidonic acid cascade and activation of nicotinic acetylcholine receptors (nAChRs), are involved in increased tumor survival. Combined application of inhibitors acting on these two pathways may result in a more pronounced antitumor effect. Here, we show that baicalein (selective 12-lipoxygenase inhibitor), nordihydroguaiaretic acid (non-selective lipoxygenase inhibitor), and indomethacin (non-selective cyclooxygenase inhibitor) are cytotoxic to Ehrlich carcinoma cells in vitro. Marine snail α-conotoxins PnIA, RgIA and ArIB11L16D, blockers of α3β2/α6β2, α9α10 and α7 nAChR subtypes, respectively, as well as α-cobratoxin, a blocker of α7 and muscle subtype nAChRs, exhibit low cytotoxicity, but enhance the antitumor effect of baicalein 1.4-fold after 24 h and that of nordihydroguaiaretic acid 1.8–3.9-fold after 48 h of cell cultivation. α-Conotoxin MII, a blocker of α6-containing and α3β2 nAChR subtypes, increases the cytotoxic effect of indomethacin 1.9-fold after 48 h of cultivation. In vivo, baicalein, α-conotoxins MII and PnIA inhibit Ehrlich carcinoma growth and increase mouse survival; these effects are greatly enhanced by the combined application of α-conotoxin MII with indomethacin or conotoxin PnIA with baicalein. Thus, we show, for the first time, antitumor synergism of α-conotoxins and arachidonic acid cascade inhibitors.

P44 l-Cysteine/H2S pathway involvement in human platelet aggregation

H2S is endogenously produced from l-cysteine (L-cys) by the action of three key enzymes cysthationine β-synthase (CBS), cysthationine-γ-lyase (CSE) and the newly discovered 3-mercaptopyruvate sulfurtransferase (3-MST) [1], [2]. It is present in human blood at micromolar concentrations [3] and it is involved in the maintenance of cardiovascular homeostasis [4]. To date, the influence of H2S on platelets, which play a central role in blood homeostasis, has been poorly explored. Therefore, we aimed to evaluate the effect of H2S signaling in human platelets. Human washed platelets were collected from 15 healthy volunteers. The expression of both CBS, CSE and 3-MST was evaluated by Western blot analysis. The enzymes activity was evaluated through H2S measurement by a colorimetric assay [5]. Light transmission aggregometry technique was used to analyze platelet aggregation. H2S-induced effect was evaluated using both an exogenous source of H2S, sodium hydrogen sulphide (NaHS, 0.1 μM–10 mM) and the metabolic precursor, L-cys (0.1 μM–10 mM) on thrombin receptor activator peptide 6 amide (TRAP-6, 2 μM) stimulus. We operated a pharmacological modulation by using specific inhibitors of arachidonic acid cascade, the main pathway involved in platelet function. Indomethacin (INDO, 10 μM, 15 min), a COX inhibitor, arachidonyl trifluoromethyl ketone (AACOCF3, 1 μM, 15 min), a phospholipase A2 (PLA2) inhibitor or SQ29548 (1 μM), a thromboxane receptor antagonist were used. In addition, thromboxane (TXA2) and cAMP levels were evaluated. Human washed platelets expressed CBS, CSE and 3-MST and generated detectable amounts of H2S. Incubation with L-cys significantly increased H2S release (p < 0.001). Neither L-cys nor NaHS (0.1 μM–10 mM) affected human washed platelets in resting conditions, but both significantly increased TRAP-6-induced aggregation (p < 0.001 for L-cys 0.1 mM and NaHS 0.1 mM and 10 μM; p < 0.01 for NaHS 1 μM and p < 0.05 for L-cys 10 μM). Besides, H2S did not modify platelet cAMP levels. Conversely, INDO, AACOCF3 and SQ29548 blocked the potentiating effect of H2S on platelet aggregation induced by TRAP-6. Interestingly, both NaHS and L-cys induced a significantly increase in TXA2production (p < 0.01). Our data imply that the H2S endogenously produced within human platelets is involved in platelet aggregation through PLA2 activation. These findings may open a new pharmacological approache in platelet dependent disorders.

Effects of arachidonate metabolism inhibitors on basal and human chorionic gonadotropin-stimulated progesterone secretion by rat corpus luteum cells in vitro

Arachidonic acid (AA) and its metabolites mediate many physiological processes including reproduction and endocrinology. The current study investigated effects of several inhibitors of AA cascade on steroidogenesis by rat corpus luteum cells in vitro. Dispersed luteal cells prepared from rat corpus luteum on day 6 of pseudopregnancy secreted progesterone (P4) in time-dependent and human chorinonic gonadotropin (hCG)-dependent fashion. Arachidonyl trifluoromethyl ketone, a preferential inhibitor of the type IVA phospholipase A 2 (PLA 2-IVA), stimulated basal P4 secretion and had no influence on hCG-stimulated steroidogenesis. A novel and more specific inhibitor pyrrophenone inhibited hCG-induced P4 secretion. A cyclooxygenase inhibitor indomethacin did not affect basal secretion but inhibited hCG-stimulated secretion. Nordihydroguaiaretic acid tended to decrease basal P4 secretion and completely inhibited hCG-stimulated secretion. Obtained results suggest that AA metabolic cascade, which is triggered at least in part by PLA 2-IVA activity, is potentially implicated in hCG-stimulated P4 secretory response in the rat corpus luteum.

Arachidonic acid cascade inhibitors modulate phorbol ester-induced oxidative stress in female ICR mouse skin: differential roles of 5-lipoxygenase and cyclooxygenase-2 in leukocyte infiltration and activation.

We recently developed a short-term assay for skin H2O2 generation induced by double 12-O-tetradecanoylphorbol-13-acetate (TPA) applications for mechanistic study on skin epidermal carcinogenesis. In the present study, we investigated the individual roles of arachidonic acid metabolism in H2O2 generation in mouse skin inflammation. The experiments using inhibitors of arachidonic acid (AA) metabolism showed that corticosteroid and a lipoxygenase (LO) inhibitor expectedly suppressed double TPA application-induced H2O2 generation through the interference of chemotactic action but not by direct decomposition or scavenging. We also demonstrated that the treatment of AA (1 mumol) and 5-LO metabolites including leukotriene B4 (LTB4) partly mimicked, though soybean LO-derived lipid hydroperoxide and prostaglandins did not, the priming effect evaluated by edema formation and leukocyte infiltration. We also confirmed that inflammatory leukocytes accumulated by LTB4 generated a significant amount of H2O2 by TPA stimulation. These results suggested that 5-LO metabolites of AA are the potential key molecules in the TPA-induced priming event. Interestingly, the cyclooxygenase (COX-) 2-selective inhibitor nimesulide (NS) and celecoxib (CXB) showed different responses than those of other inhibitors. These agents showed no specific potential to inhibit the priming event but significantly suppressed H2O2 generation, lipid peroxidation, and hyperplasia in mouse skin. From the results based on an in vitro leukocyte differentiation model, we speculated that the antioxidant effect of the COX-2 inhibitors might be partly associated with both counteraction of proinflammatory cytokine-enhanced ROS generation and inhibition of CD11b, an important molecule for cell adhesion, expression. Indeed, the topical application of NS attenuated the number of infiltrated leukocytes induced by TPA in mouse skin. Thus, these gathered data indicated the differential roles of 5-LO and COX-2 in leukocyte adhesion, infiltration, and H2O2 generation.

Participation of the Arachidonic Acid Cascade Pathway in Macrophage Binding/Uptake of Oxidized Low Density Lipoprotein.

Arachidonic acid cascade inhibitors, including phospholipase A2 inhibitors, dexamethasone and quinacrine (mepacrine), cyclooxygenase inhibitors, indomethacin and aspirin, and lipoxygenase inhibitor AA861, prevented foam cell formation and cholesterol accumulation in the incubation of thioglycollate-induced mouse peritoneal macrophages with oxidized low density lipoprotein (LDL) at 37 degrees C for 24 h. These inhibitors similarly prevented foam cell formation of fibronectin- and Ca ionophore A23187-stimulated macrophages. Binding and/or uptake of Dil (1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine)-acetyl LDL by macrophages at 37 degrees C for 3h and arachidonic acid release from macrophages at 37 degrees C for 4h were inhibited by dexamethasone. Exogenously added phospholipase A2 of bee venom and Crotalus adamanteous venom increased arachidonic acid release during incubation for 2 h, and increased macrophage binding and/or uptake of Dil-acetyl LDL at 37 degrees C for 3 h, and foam cell formation at 37 degrees C for 24 h. Protein kinase inhibitors, ML-9 and staurosporine, that inhibited macrophage binding and/or uptake of Dil-acetyl LDL did not inhibit arachidonic acid release, indicating that protein phosphorylation was not involved in the arachidonic acid pathway in the macrophage scavenger receptor activation. Nordihydroguaiaretic acid that inhibited arachidonic acid release prevented binding and/or uptake of Dil-acetyl LDL. The release of arachidonic acid was not enhanced by fibronectin-stimulation, indicating that Ca influx-dependent stimulation of macrophage activity was not through the activation of phospholipase A2. These results indicate that, as well as the fibronectin-stimulated Ca influx pathway and protein phosphorylation pathway, the arachidonic acid pathway participated in the activation of macrophages to bind and take up oxidized LDL.

Prevention by inhibitors of arachidonic acid cascade of liver carcinogenesis, cirrhosis and oxidative DNA damage caused by a choline-deficient, l-amino acid-defined diet in rats

Effects of inhibitors of arachidonic acid (AA) cascade on the development of fatty liver, cirrhosis, glutathione S-transferase placental form (GST-P)-positive preneoplastic nodules, neoplastic nodules and generation of 8-hydroxyde-oxyguanosine (8-OHdG), caused by a choline-deficient, l-amino acid-defined (CDAA) diet, were examined in Fischer 344 male rats by feeding CDAA diet supplemented with the inhibitors for 12 and 30 weeks. None of the inhibitors affected fatty liver. Among cyclooxygenase (COX) inhibitors, an irreversibly acting acetylsalicylic acid and a long-acting piroxicam, and to a much lesser extent the short-acting ibuprofen but not indomethacin, inhibited the development of cirrhosis, GST-P-positive and neoplastic nodules and generation of 8-OHdG. A phospholipase A 2 inhibitor p-bromophenacylbromide (BPB) also exerted similar but lesser extent of inhibitory effects. Lipoxygenase inhibitors quercetin and nordihydroguiaretic acid inhibited GST-P-positive nodules but not cirrhosis or 8-OHdG. Present results suggest that perturbed AA cascade, particularly augmented COX pathway, might play key roles in the causation of liver lesions in the CDAA diet model.

Synergistic effects of 13- cis retinoic acid and arachidonic acid cascade inhibitors on growth of head and neck squamous cell carcinoma in vitro

Products of arachidonic acid metabolism can influence normal and malignant cell growth. In vivo, inhibitors of arachidonic acid metabolism have been associated with inhibition of tumor growth, including head and neck squamous cell carcinoma (HNSCC). This has not been evaluated extensively in vitro in an HNSCC model. Therefore we investigated the effects of several arachidonic acid cascade inhibitors (AACIs) (indomethacin, curcumin, phenidone, nordihydroguaiaretic acid, 5,8,11,14-eicosatetraynoic acid, and 13-cisretinoic acid) on the growth of two HNSCC cell lines (MDA 886Ln and 1483). We found that AACIs caused dose-dependent growth inhibition of both cell lines. In an effort to inhibit HNSCC cell growth at lower concentrations of these drugs, we evaluated the effects of a variety of AACIs in combination with 13-cis retinoic acid. We observed synergistic growth inhibition when the drugs were used in all combinations, with the exception of indomethacin. These results suggest that AACIs may have some utility in the direct treatment of HNSCC, and a strategy combining 13-cis retinoic acid with other AACIs may prove to be even more effective.

The possible involvement of protein kinase C and phospholipase A2 inHydra tentacle regeneration

The participation of protein kinase C (PKC) in the regeneration of tentacles ofHydra vulgaris was studied. Regeneration was induced by 1,2-sn-dioctanoyl-glycerol (diC8) and the novel diterpenoidic diacylglycerol verrucosin B (VB), a potent PKC activator extracted from marine sources. VB substantially increasedHydra average tentacle number (ATN) at concentrations 10,000 times lower than those needed for diC8 to exert an analogous effect. When both synthetic and natural VB analogues were tested, the structure/activity relationship found inHydra tentacle regeneration was identical to that known for DAG-induced activation of PKC in vitro. VB-induced increase of ATN was strongly counteracted by the PKC inhibitors sphingosine and A3, but was not synergic with a tenfold increase of extracellular Ca2+ concentration or with an increase of intracellular Ca2+ concentration obtained either with the ionophore A23187 or with thapsigargin. This suggested the involvement of a non-Ca2+-dependent PKC in VB-triggeredHydra tentacle regeneration. The involvement of phospholipase A2 (PLA2) activation inHydra regenerative processes was studied using the novel site-specific inhibitor of the enzyme, oleyloxyethylphosphorylcholine (OOPC), which brought about a striking inhibition of ATN in the low μmolar range. This effect was reversed by arachidonic acid (AA), while an enhancement of ATN was also observed with an inhibitor of AA uptake from membrane phospholipids, thus suggesting that PLA2-catalysed liberation of AA is involved inHydra tentacle regeneration. OOPC also blocked verrucosin B-induced PKC-mediated enhancement of ATN, thus suggesting that this effect is also mediated by PLA2 activation. ATN was increased also by compound 48/80, a direct activator of pertussis toxin-sensitive GTP-binding proteins, and this effect was counteracted by pertussis toxin pretreatment. None of the known AA cascade inhibitors exhibited an effect on ATN comparable to that exerted by OOPC, but, surprisingly, the cycloxygenase inhibitor indomethacin strongly enhanced ATN, thus suggesting that prostanoids might effect a negative control onHydra regenerative processes. This represents the first attempt so far reported to study the implication of more than one biochemical pathway as a signalling event in the hydroid regenerative processes.

Involvement of arachidonic acid cascade pathways in interleukin-6-stimulated corticotropin-releasing factor release in vitro.

We have demonstrated that centrally administered interleukin-6 (IL-6) stimulates adrenocorticotropin (ACTH) secretion by a direct effect on corticotropin-releasing factor (CRF) release from the hypothalamus. Since metabolites of the arachidonic acid cascade (AAC) have been implicated in mediating actions of cytokines in different tissues and some AAC inhibitors were able to block pyrogenic effects of cytokines and suppress IL-1-induced ACTH secretion, we decided to examine the mechanism of IL-6 action on CRF release in vitro. After a 60-min preincubation in Krebs-Ringer bicarbonate buffer, medial basal hypothalami (MBH) were preincubated for 30 min with dexamethasone (DEX), a phospholipase A2 (PLA2) inhibitor, to block arachidonic acid (AA) formation, or with inhibitors of AA metabolism: a cyclooxygenase inhibitor--indomethacin (IND); a lipoxygenase inhibitor--5,8,11-eicosatriynoic acid (ETI), and an epoxygenase inhibitor--clotrimazole (CLO). Then, the medium was discarded and MBH were incubated with medium or the above compounds and/or IL-6 for 30 min, and CRF release into the incubation medium was measured by radioimmunoassay. As reported previously, 10(-13) M IL-6 increased CRF release, which was significantly suppressed by DEX in a dose-dependent manner. The suppression was already highly significant at a concentration of 10(-11) M DEX and became maximal at 10(-7) M, at which concentration CRF release was no longer stimulated by IL-6. The response to IL-6 was completely blocked at the highest DEX concentration evaluated (10(-5) M). CLO also suppressed IL-6-induced CRF release with a minimal effective dose of 10(-9) M. Suppression was complete at 10(-7) and 10(-5) M.(ABSTRACT TRUNCATED AT 250 WORDS)

Benzo[A]pyrene-induced oxidative DNA damage in human mammary epithelial cells: Effects of metabolic intermediates and arachidonic acid cascade inhibitors

Benzo[A]pyrene-induced oxidative DNA damage in human mammary epithelial cells: Effects of metabolic intermediates and arachidonic acid cascade inhibitors

Chemiluminescent response in murine peritoneal macrophage hybridoma-cell line (2C11-12) primed with lipopolysaccharide or interferon β

Chemiluminescent (CL) response of the unprimed, and lipopolysaccharide (LPS) and interferon (IFNβ) primed murine peritoneal macrophage 2C11-12 cell line to inactive and active tumor promoters was studied. A 48-h treatment of cells with LPS at 100 ng/ml and IFNβ at 50 U/ml (units per milliliter) augmented CL response to active tumor promoters (PMA, PHB, PDBu, PDBz, MEZ) significantly by 8- to 10-fold. Inactive tumor promoters (PDA, MPMA) failed to elicit any CL responses. Kinetics of CL responses to tumor promoters were similar between unprimed and LPS/IFNβ primed macrophages. The levels of H 2O 2 and .[O 2] − were undetectable using scopoletin and cytochrome c reduction assays, respectively. The CL response, however, in the presence of bystander lucigenin, specific for .[O 2] − or mannitol, a specific inhibitor of [.OH], was inhibited by 25%. Inhibitors of arachidonic acid cascade, AA861, a specific inhibitor of 5′-lipoxygenase; indomethacin, an inhibitor of the cyclooxygenase pathway; and NDGA and BW755C, inhibitors of lipoxygenase and cyclooxygenase pathways, strongly inhibited the CL response in both LPS and IFNβ primed macrophages. The results of this study suggest that the enhancement of PMA-induced CL response in LPS/IFNβ primed macrophages is possibly through modulation of enzymes regulating arachidonic acid metabolism.

Influence of inhibitors of arachidonic acid cascade on interleukin-1 (IL-1) release

Influence of inhibitors of arachidonic acid cascade on interleukin-1 (IL-1) release

Potentiation of PGE1-induced increase in cyclic AMP by chemotactic peptide and Ca2+ ionophore through calmodulin-dependent processes.

The interaction between prostaglandin E1 (PGE1) and chemotactic peptide formylmethionyl-leucyl-phenylalanine (fMLP) in cAMP production in guinea pig neutrophils was investigated. Both PGE1 and fMLP increased the cAMP content in neutrophils. At low concentrations of PGE1 (less than 10 nM), the effects of fMLP and PGE1 in stimulating cAMP accumulation were additive, but at high concentrations of PGE1, their effects were synergistic. The effects of PGE1 and Ca2+ ionophore A23187 instead of fMLP on cAMP accumulation were also synergistic. The synergy did not appear to be related to change in cyclic nucleotide phosphodiesterase activity, because it was still marked in the presence of isobutyl-3-methyl-1-xanthine, a phosphodiesterase inhibitor. Studies on the time course of PGE1-induced cAMP accumulation showed that cAMP production ceased within 5 min after the addition of high concentrations of PGE1. The period of cAMP production could not be prolonged by combined treatment with PGE1 and fMLP or Ca2+ ionophore A23187. The synergy was found to be caused through Ca2+-dependent processes, because depletion of the medium of Ca2+ and addition of the Ca2+ antagonist TMB-8 inhibited the synergistic increase in cAMP. Moreover, the calmodulin antagonist W-7 also effectively inhibited the synergistic increase in cAMP. These results suggest that the potentiation of PGE1-induced cAMP production by fMLP or Ca2+ ionophore A23187 is catalyzed by calmodulin-dependent processes. However, the synergistic increase in cAMP production was not inhibited by arachidonic acid cascade inhibitors such as indomethacin, BW755C, or nordihydroguiaretic acid, and a combination of PGE1 and a protein kinase C activator, tetradecanoyl phorbol acetate (TPA), did not cause synergistic increase in cAMP. Marked increase in cAMP was also induced by a combination of cholera toxin and fMLP or Ca2+ ionophore A23187, but not by a combination of forskolin and fMLP or Ca2+ ionophore A23187. The synergistic increase in cAMP was not sustained in isolated membranes. On the contrary, PGE1-induced cAMP production in isolated membranes was suppressed by their pretreatment with fMLP or Ca2+ ionophore A23187. These data suggest that the synergistic effects of PGE1 and fMLP or Ca2+ ionophore in increasing the cAMP level are due to potentiation of PGE1-induced cAMP production by Ca2+ and calmodulin-dependent processes.

Antitumor effects of inhibitors of arachidonic acid cascade on experimentally induced intestinal tumors.

The antitumor action of inhibitors of cyclooxygenase (indomethacin) and lipoxygenase activity (nordihydroguaiaretic acid) of arachidonic acid cascade was investigated in the chemically induced large bowel tumors in Sprague-Dawley rats. Indomethacin treatment completely prevented the carcinogenic effect of methylazoxymethanol. Thus, no tumors were found in the 14 rat test group, compared with 13 of 14 tumor-bearing rats in the untreated control group. Although nordihydroguaiaretic acid treatment does not abolish prostaglandin synthesis, it does reduce the effect of the carcinogen and tumors were found in only five of 14 treated rats. From this study it can be postulated that not only is reduction in prostaglandin formation responsible for the inhibition of tumor growth, but also leukotrienes may play some role.

Modulation of acetylcholine release from guinea-pig Ileum myenteric plexus by arachidonic acid cascade inhibitors.

Effects of arachidonic acid and mepacrine on ACh release from guinea-pig ileum myenteric plexus were investigated. Mepacrine (1-8 microM) inhibited the ACh release in a concentration-dependent manner. Arachidonic acid counteracted the inhibitory effect of mepacrine, but PGE2 did not. The inhibition induced by a combination of mepacrine and indomethacin on nicotine-induced ACh release was prevented by arachidonic acid, while that on spontaneous ACh release was prevented by arachidonic acid and PGE2 added simultaneously. The roles of arachidonic acid and PGs in the ACh release will be discussed.

Modulation of Acetylcholine Release from Guinea-Pig Ileum Myenteric Plexus by Arachidonic Acid Cascade Inhibitors

Effects of arachidonic acid and mepacrine on ACh release from guinea-pig ileum myenteric plexus were investigated. Mepacrine (1–8 μM) inhibited the ACh release in a concentration-dependent manner. Arachidonic acid counteracted the inhibitory effect of mepacrine, but PGE2 did not. The inhibition induced by a combination of mepacrine and indomethacin on nicotine-induced ACh release was prevented by arachidonic acid, while that on spontaneous ACh release was prevented by arachidonic acid and PGE2 added simultaneously. The roles of arachidonic acid and PGs in the ACh release will be discussed.

Dual effect of (-)-N6-phenylisopropyl adenosine on guinea-pig trachea.

The effect of (-)-N6-phenylisopropyl adenosine (PIA), a metabolically stable P1-receptor agonist, was investigated on guinea-pig isolated trachea. PIA showed two opposite effects: contraction, evident at low concentrations (10(-7) to 2-5 X 10(-6) M), and relaxation at higher doses. Relaxation by PIA was antagonized in an apparently competitive manner by two antagonists of extracellular (P1) adenosine receptors: theophylline (Theo) and 8-phenyltheophylline (PT). Contraction by PIA was not inhibited by methylxanthines and was not mediated by stimulation of cholinergic or histaminergic systems. Inhibitors of arachidonic acid cascade acting at different levels, i.e. indomethacin, nordihydroguaiaretic acid (NDGA) and BW755C, all inhibited the contraction by PIA, while they potentiated the relaxation in a concentration-dependent manner. Mepacrine, an inhibitor of phospholipase A2, inhibited the contraction by PIA, but did not affect the relaxation. These results indicate that the contractile effect induced by PIA is supported by an indirect mechanism involving the release of arachidonic acid derivatives (via P2-purinoceptor?). Thus the balance between the two opposite effects of adenosine on tracheal tone is possibly modulated by the prostaglandin turnover.