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Leukotrienes mediate several inflammatory events such as neutrophil chemoattraction, leukocyte adhesion, and central-release of cytokines and fever. However, there is no information available about their putative role in lipopolysaccharide (LPS) tolerance. The rational of the present study was to find out if central leukotrienes are involved in the development of LPS tolerance. Thus, we inhibited central leukotriene synthesis in tolerant rats using a pharmacological tool, i.e., a selective inhibitor of leukotriene synthesis MK-886 injected into the third ventricle (3V) of rats. Body core temperature (Tb) was measured using a datalogger placed inside the abdominal cavity. A low-dose of LPS (100 μg/kg ip) was given for 4 consecutive days to induce LPS tolerance. At day 4, rats received a microinjection of MK-886 into the 3V immediately before LPS, whereas control groups were treated with vehicle (saline). We observed that LPS failed to induce plasma cytokines surges, increased hypothalamic PGE2 levels and fever 3 days post LPS treatment, aptly characterizing the tolerance. When MK-886 was given to control rats treated with saline, no significant change in Tb was observed. However, a full LPS-induced fever was observed in tolerant rats pretreated with MK-886, which was associated with an enhancement in the hypothalamic PGE2 levels, that were not accompanied by plasma cytokines (IL-1β, and IL-6) and PGE2 surges. These data are consistent with the notion that central leukotrienes play a role in fever tolerance to LPS.

UNLABELLED: Sjogren-Larsson syndrome (SLS) is a neurocutaneous autosomal recessive disease caused by fatty aldehyde dehydrogenase (FADH) deficiency. This enzyme is involved in the biosynthesis pathways of some fatty acids, phytanic acid, and leukotrienes. The main features of the disease are its association with congenital ichthyosis, mental retardation, and spastic tetraplegia. METHODS: We report on the diagnostic and therapeutic management of 2 cases of SLS. RESULTS: The diagnosis of SLS was suspected in the first patient at 2 years of age before the clinical triad appeared and confirmed at 4 years of age by the culture of fibroblasts and the peak of lipids on 1.3 ppm spectroscopy. After 3 months of treatment with zileuton, an inhibitor of leukotriene synthesis, moderate clinical efficacy for pruritus and ichthyosis was observed. The second patient was diagnosed at 1 year of age with the association of psychomotor retardation and congenital ichthyosis, in accordance with acute Guillain-Barre syndrome. Diagnosis was confirmed with enzymology, and cerebral spectro-MRI featured an abnormal lipidic peak. Zileuton therapy was initiated at the time of diagnosis and was effective for pruritus after 6 months of treatment. CONCLUSION: We report 2 cases of SLS with delayed diagnosis, due to non neonatal symptoms. Treatment with zileuton shows partial efficacy especially in pruritus. The uncommon association of this rare dysmyelinating disease with Guillain-Barre syndrome in the second patient is discussed.

Recently, there has been great progress in elucidating the biochemistry of the arachidonic acid (AA) metabolism. The abnormal production of leukotrienes (LTs), due to the unbalanced-regulation of synthesizing and catabolizing enzymes, is probably induced by many bioactive substances, including Th2 cell-derived cytokines. Imbalances in these processes may play an important role in allergic reactions and other inflammatory diseases, thus making them potentially prime therapeutic targets for these diseases. Further studies on the regulation of LT-synthesis and catabolism are therefore required to clarify the importance of these imbalances on the initiation and progression of allergic and inflammatory diseases.

Urinary leukotriene E4 (LTE4) has been used as an index of total leukotriene synthesis. A wide variety of methods have been applied to measure LTE4 which has made direct comparison of urinary levels reported by different laboratories difficult. A new peptidoleukotriene immunoaffinity resin was utilized for urinary LTE4 purification in a method that is easy and inexpensive, utilizing commercially available reagents. This method is described and compared to other methods. LTE4 (50–250 pg/mL) added to a urine extract was quantitatively recovered using the immunoaffinity resin. Similarly, LTE4 (50–400 pg/mL) added to urine was recovered between 63 and 76%. The coefficient of variation of samples purified and quantified on the same or on different days ranged from 8–10%. There was a strong correlation (r2 = 0.95) between LTE4 concentrations determined after immunofiltration and immunoaffinity purification. Although there was a good correlation between urinary LTE4 levels measured without purification compared to after immunoaffinity purification, the high y-intercept of 179 indicates the presence of interfering substances in unpurified urine. Urinary LTE4 in normal healthy adults was 80 ± 7 pg/mg creatinine, similar to that previously reported following HPLC or immunofiltration purification. Urinary LTE4 was also measured in healthy children (age 3–12) and found to be 103 ± 9.

The synthesis of leukotriene B4 by A23187-stimulated rat peritoneal leukocytes was studied in the presence of 0.1% normal human serum, serum from patients treated with NSAIDs for either an inflammatory (rheumatoid arthritis, RA) or a non-inflammatory condition (lumbar disc protrusion, LDP), and serum from RA patients drawn one week after withdrawal from NSAID treatment. The capacity for LTB4 synthesis was significantly lower in the presence of serum from NSAID treated patients: thirty per cent less than observed in presence of normal serum in the RA group, and fifty per cent in the LDP group. When NSAIDs were withdrawn from RA patients, the LTB4 production in presence of serum increased, but was not completely normalized after one week. These results indicate that NSAID treatment may down-regulate the capacity for leukotriene synthesis by an indirect effect.

A series of 5-hydroxyphenylpyrrolo-1,4-benzoxazine derivatives substituted by a pyridinylpiperazinyl alkyl chain were designed as multimediator compounds with potential antiasthmatic properties. These compounds were prepared and evaluated both in vitro against leukotriene synthesis and PAF activity and in vivo against histamine. Structure-activity relationships led to compound 11 which displayed the most potent activities in this series.

Evidence on aetiology in multiple sclerosis suggests that the prevalence depends on the interaction of two factors, diet and exposure to visible sunlight. The dietary features which may be beneficial include supplementation with fish oils, avoidance of saturated fats, and the associated intake of antioxidants with unsaturated fatty acids. Inhibition, by antioxidants, of the enzyme lipoxygenase inhibits leukotriene synthesis, and the presence of fish oils leads to the production of leukotrienes with less inflammatory properties. This is of particular importance in the retina where leukotrienes might be the underlying cause of retrobulbar neuritis. The antioxidant properties of vitamin A may also lead to inhibition of leukotriene synthesis. Visible solar radiation could be of benefit therefore by releasing vitamin A from visual pigment rhodopsin. The interaction of these two factors may explain the epidemiological observations on the prevalence of multiple sclerosis.

Administration of the leukotriene synthesis inhibitors nordihydroguaiaretic acid (NDHGA, 30 mg/kg), caffeic acid (20 mg/kg) or nafazatrom (100 mg/kg) and of the phosphodiesterase inhibitor and free radical trapper dipyridamole (10 mg/kg) prevented the alterations in enzyme activity displayed by acute CCl4 administration. The effect was less evident in preventing hepatic glycogen depletion or lipid peroxidation. A synergistic protective effect between dipyridamole and NDHGA or caffeic acid was observed. In conclusion, the present results show that acute hepatic damage induced by CCl4 can be partially prevented by leukotriene synthesis inhibitors and the protection is enhanced with the simultaneous use of phosphodiesterase inhibitors.

Methyl 5S -(benzoyloxy)-6-oxohexanoate 2 , an intermediate in synthetic routes to the lipoxygenase-derived arachidonic acid metabolite leukotriene B 4 , is available in three steps from 2-cyclohexen-1-one, using Schreiber's unsymmetrical ozonolysis protocol.

Signalling pathways that regulate the expression of plant genes are poorly understood. Recent evidence indicates that octadecanoid-derived signals may be parts of signalling pathways in plants in which C 18 fatty acids, liberated from membranes in response to environmental or developmental cues, are converted to intracellular signalling molecules such as jasmoric acid and traumatin. These events are analogous to prostaglandin and leukotriene synthesis in animals.

Leukotrienes are bioactive lipid metabolites involved in respiratory and cardiovascular diseases. They are synthesized from arachidonic acid by the enzyme 5-lipoxygenase, and the integral membrane protein 5-lipoxygenase–activating protein (FLAP) plays an essential role in their biosynthesis. Ferguson et al . describe the crystal structure of human FLAP in complex with two different leukotriene biosynthesis inhibitors. The structures suggest how the inhibitors prevent arachidonic acid from binding to FLAP, from which it is likely transferred to 5-lipoxygenase. The structural data provide a basis for the development of drugs targeted against FLAP that would inhibit leukotriene biosynthesis. A. D. Ferguson, B. M. McKeever, S. Xu, D. Wisniewski, D. K. Miller, T.-T. Yamin, R. H. Spencer, L. Chu, F. Ujjainwalla, B. R. Cunningham, J. F. Evans, J. W. Becker, Crystal structure of inhibitor-bound human 5-lipoxygenase-activating protein. Science 317 , 510-512 (2007). [Abstract] [Full Text]

Cell-substrate and cell-cell adhesion of neutrophils has been found to slow down the calcium ionophore A23187-induced synthesis of 5-lipoxygenase (5-LO) metabolites of arachidonic add. Addition of the exogenous substrate, arachidonic acid (AA), together with A23187, resulted in the enhanced production of leukotriene B4 (LTB4) and 5-hydroxyeicosatetraenoic acid (5-HETE) by adherent neutrophils in comparison with those by the cells in suspension. We observed also the enhanced production of 5-LO metabolites in attached cells when we stimulated the cells by the combined action of phorbol 12-myristate 13-acetate (PMA) and A23187. Thus, the adhesion to solid substrate and to other cells, an important regulatory factor for the activity of many cells, is a powerful regulator of leukotriene production by neutrophils.

There is good evidence from a number of cellular systems that the rate-limiting step of the arachidonic acid cascade consists in the release of arachidonate from phospholipids. At first sight, prostaglandin H synthase (PGHS) seems to be unrestricted under cellular conditions and the lipoxygenases although being partially dependent on Ca2+ are not limiting since phospholipase A2 requires Ca2+-levels that are higher than those for lipoxygenases as recently shown for leukotriene synthesis in leukocytes (1).

The importance of locally produced prostaglandins (PGs) in the inflammatory response has been well recognized since the observation by Vane and colleagues that aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) inhibit PG synthesis1–3. More recently, it has been suggested that other products of arachidonic acid metabolism, such as leukotrienes, are also mediators of allergic and inflammatory reactions. Inhibitors of leukotriene synthesis and antagonists of their action have recently been developed and are presently undergoing clinical evaluation; the exact role and importance of these mediators in human disease will be clarified only when the outcome of these clinical studies is known. In this review we will describe the pharmacological effects of selective lipoxygenase inhibitors in tests conducted in animals, and will discuss the possible relevance to humans.

Soluble rat liver glutathione S-transferases have been purified and a previously undescribed peak was observed. This peak contained glutathione S-transferase activity which was extensively inhibited by indomethacin. Glutathione conjugation of 1-chloro-2,4-dinitrobenzene by this isozyme, designated glutathione S-transferase VII, was inhibited 44 and 68% at indomethacin concentrations of 0.20 and 1.00 microM, respectively. The other six basic glutathione S-transferase isozymes were relatively unaffected by low concentrations of indomethacin. The pharmacological significance of this inhibition by indomethacin is largely dependent on the role of the glutathione S-transferase VII in leukotriene synthesis.

It would appear that it has become almost common practice to regard arachidonic acid (AA) as the sole precursor of eicosanoids. The fact that both dihomogamma-linolenic acid (DGLA) and eicosapentaenoic acid (EPA) give rise to destinct families of eicosanoids is commonly almost completely ignored. Elevated tissue levels of AA eicosanoids have been found in and have been implicated in the etiology of a number of diseases. Drugs which selectively block AA mobilization or its eicosanoid metabolism have therefore been developed for therapeutic use in these conditions. The fact that such drugs will also simultaneously block the eicosanoid metabolism from DGLA as well as from EPA is also commonly ignored. It is suggested that the profoundly adverse side-effects displayed by some of these drugs, resulting in some instances in theirwith-drawal from use, could be the direct result of their concomitant action of interfering with the eicosanoid metabolism of DGLA and EPA. It is further suggested that, before the interactions between the eicosanoids derived from AA and those derived from DGLA and EPA are understood, the use of drugs for the manipulation of AA eicosanoid metabolism in isolation, could be hazardous. This implies that all such drugs currently in use are to be regarded as experimental and provisionally toxic in terms of their effects on the whole system of eicosanoid metabolism. Thus even drugs which have been passed by the FDA and similar Drug Control Councils require total re-evaluation especially in view of the fact that the non-steroidal anti-inflammatory drugs are often prescribed for chronic conditions which require therapy for several years. Finally, it is pointed out that the use of drugs to suppress AA metabolism should become superfluous in subjects where such therapy is deemed necessary, by the adoption of a dietary supplementation regimen with gamma-linolenic acid (GLA) and EPA.

In an investigation of the pathogenesis of acute necrotizing pancreatitis (ANP) the plasma levels of TXB2, 6-keto-PGF1 alpha, and PGE2 were measured in rats. After induction of ANP by injection of 5% sodium taurocholate into the pancreatic duct, a marked increase in TXB2 levels and a slight increase in 6-keto-PGF 1 alpha levels were found. PGE2 levels decreased. Mortality was 100% within 30 h. Pretreatment with chloroquine, a phospholipase A2 inhibitor, led to a inhibition of TXB2 production, whereas 6-keto-PGF1 alpha and PGE2 levels showed a surprising slight elevation in the first 6 h. Pretreatment with chloroquine decreased mortality by 30%. Pretreatment with FPL 55712, a leukotriene synthesis blocker, caused an increase in TXB2 and PGE2 levels, whereas the formation of 6-keto-PGF1 alpha remained unaltered. Two out of nine animals survived after pretreatment with FPL 55712. The results of the present study indicate that arachidonate end products are involved in ANP. The significance of the high TXB2 levels, decreased PGE2 levels, and only slightly elevated 6-keto-PGF1 alpha levels during ANP requires further investigation. The thromboxane A2 to prostacyclin ratio may be important.

The regional distribution of ionophore A23187-induced synthesis of leukotrienes and mono-hydroxyeicosatetraenoic acids in the rat brain in vitro was investigated. Pronounced differences in leukotriene C4 formation were observed, with the highest synthetic capacity in the hypothalamus. The formation of leukotriene C4 was about 12-times higher in the hypothalamus as compared to the cerebellum. This finding is in agreement with a possible neuroendocrine role for leukotriene C4. In contrast, the activity of leukotriene B4 synthesis was widely distributed without pronounced regional differences in the rat brain. Formation of 5-, 9-, 11-, 12- and 15-monohydroxyeicosatetraenoic acid was detected in all regions. The major lipoxygenase product in the hypothalamus and thalamus was 5-hydroxyeicosatetraenoic acid, while other monohydroxyeicosatetraenoic acids predominated in the remaining regions tested.

During the last 25 years prostaglandins and, more recently, leukotrienes have commanded increasing interest in the field of medical research. The identification of these substances as potent local hormones which contribute to many physiological and pathological processes has made them the target for potential new therapies. An understanding of the origin of prostaglandins and leukotrienes has led to the suggestion that dietary manipulation could be a means of controlling their synthesis and that this may be of prophylactic value in diseases such as thrombosis and arthritis. In the present paper I shall discuss the relation between essential fatty acids, prostaglandins and leukotrienes and indicate how essential fatty acid intake could influence events in the development of thrombotic and inflammatory disorders.

The IgE-mediated hypersensitivity to Ascaris antigen in reactor rhesus primates was used to assess the pharmacologic profile of U-60,257, a pyrrole analog of prostacyclin. Whether the compound was given by aerosol or intravenously, it effectively inhibited the bronchopulmonary effects of antigen challenge. Dose responses by the aerosol route showed a dose-dependent inhibition of resistance (RL) and compliance (Cdyn) changes (100% ± 0 to 10.2% ± 14.5 for RL and 79.9% ± 20 to 0% for Cdyn after 15 breaths of 1.0–0.01 % solutions delivered into the lungs; n = 16). When administered at 1.0% by aerosol the duration of the inhibitory effect was 6 h (n = 3). Dose-dependent inhibition in both RL (93.3% ± 5.6 to 69.4% ± 34.8) and Cdyn (51.4 ± 40.4 to 47.0% ± 28.5) was also seen when the compound was given intravenously (5.0–0.01 mg/kg; n = 16). U-60,257 is a selective inhibitor of leukotriene synthesis in in vitro systems. Therefore, the finding of synergism in the inhibition of response of primates to Ascaris between this compound and the H1 histamine blocker diphenhydramine suggests that the leukotrienes may play an etiologic role in this response.

The IgE-mediated hypersensitivity to Ascaris antigen in reactor rhesus primates was used to assess the pharmacologic profile of U-66,858 (1-acetoxy-2-n-butyl-4-methoxy-naphthalene). When the compound was given by the oral route, it showed dose-related inhibition of resistance (RL) and compliance (Cdyn) changes. When the compound was given by the aerosol route, it showed dose independent inhibition. In 15 animals, aerosols (52 ± 32 to 53 ± 10% for RL, p = 0.05 and 45 ± 19 to 28 ± 19% Cdyn inhibitions, p = 0.05) for 5.0–0.1% aerosol. By the oral route, inhibition was seen at 1–4 h following administration. In 5 animals, oral doses of 10 and 5 mg/kg inhibited (RL by 98 ± 2 to 78 ± 1.5 %, p = 0.01 and Cdyn by 75 ± 17 to 60.9 ± 9.1 %, p = 0.05) by 10 and 5 mg/kg U-66,858, respectively. The in vivo demonstration of inhibition of pulmonary bronchoconstriction by this compound, in a model known to be leukotriene sensitive, coupled with its potent in vitro inhibition of 5-lipoxygenase enzymes, suggests this compound may be of use in 5-lypoxygenase-mediated models of asthma.

2,3,5-Trimethyl-6-(12-hydroxy-5,10-dodecadiynyl)-l,4-benzoquinone (AA861) inhibited 5-lipoxygenase of guinea pig peritoneal polymorphonuclear leukocytes (ID50, 0.8 μM). The inhibition was of competitive type. 12-Lipoxygenases and fatty acid cyclooxygenase were not affected below 10 μM. The formation of slow-reacting substance of anaphylaxis by the sensitized guinea pig lung was almost fully suppressed by the compound at 10 μM.

A series of 3-(3,5-di-tert-butyl-4-hydroxybenzylidene)pyrrolidin-2-ones was synthesized and evaluated as candidate antiinflammatory/analgesic agents as well as dual inhibitors of prostaglandin and leukotriene synthesis. Some compounds that showed dual inhibitory activity were found to possess equipotent antiinflammatory activities to indomethacin, with reduced ulcerogenic effects. One of the compounds, N-methoxy-3-(3,5-di-tert-butyl-4-hydroxybenzylidene)pyrrolidin-2-o ne, was found to have a wider safety margin than indomethacin or piroxicam, and was selected for detailed evaluation as a candidate drug for clinical application.

Inhibitors of platelet activating factor (PAF) and leukotriene synthesis or action are of interest as potential anti-asthmatic drugs. The present study outlines evidence suggesting an interaction between PAF and lipoxygenase products mediating increased airways responsiveness to histamine in vivo.

Methyl (5 SR , 6 SR )-5-hydroxy-6-phenylselenyleicosa- cis,cis,cis -8,11,14-trienoate ( 8 ), available in two steps from arachidonic acid, undergoes oxidative deselenylation to give selectively either methyl (5 SR )-5-hydroxyeicosa- trans,trans,cis,cis -6,8,11,14-tetraenoate ( 5 ) or its cis -8 isomer ( 6 ), depending upon the reaction conditions.

Actions of endotoxin (1ipopolysaccharide, LPS) in vivo have long been suggested to be mediated by arachidonate metabolites (1,2). The important role of arachidonate-derived metabolites including leukotrienes, prostaglandins and thromboxane in experimental LPS shock has been deduced from the LPS resistance of essential fatty acid-deficient rats (3,4), from the altered arachidonate metabolism in LPS-tolerant rats (5), as well as from pharmacological evidence (1,2,6,7). Recent studies showed that the LPS-resistant C3H/HeJ mouse strain, whose macrophages are defective in prostaglandin (8,9) and leukotriene synthesis (10), can be made highly LPS-sensitive by transfer of pure macrophages from LPS-sensitive C3H/HeN mice (11). These data stress the target cell role of macrophages in the in vivo action of LPS (8,11).

The role of arachidonic metabolites in the control of immunity in inflammation is reviewed with particular emphasis on the most recent observations and possible interactions between these products and other mediators. Continuing studies on the nature of the lipoxygenase involved in leukotriene synthesis will be discussed as will the nature of the enzymatic activity involved in the transfer of sulphur in leukotriene C, D and E.

Pretreatments of rats with the Carbochromene derivative AD 6 (4 mg/kg i.p., 2 h before sacrifice) resulted in elevation of brain levels of 6-keto-PGF 1α in cerebral cortex under physiological conditions, had no effect on levels of TxB 2 and 6-Keto-PGF 1α at 30 min of hypoxia (respiration of 5% O 2 in N 2 ) and prevented the accumulation of TxB 2 occurring in brain at 5 min of recovery after hypoxia. In addition, the accumulation of LTC 4 and B 4 in brain sices incubated in the presence of the Ca ++ ionophore A23187 and arachidonic acid, was reduced in samples obtained from pretreated rats. The drug, thus, had favourable effects on the 6-keto-PGF 1α /TxB 2 ratio in normal conditions, as well as in conditions of altered oxygen supply. In addition it reduced the formation of compounds, the leukotrienes, which may exert pro-inflammatory activities on the cerebral microcirculation.

Higher concentrations of TA were needed to inhibit chemiluminescence than LTB4 formation (whereas indomethacin and timegadine reduced these two phenomena with similar potencies) suggesting a specific blockade of 5-lipoxygenase by TA. Oral TA decreased leukotriene production in PMNsex vivo. This may be related to the good anti-inflammatory and anti-migraine actions of TA, and partly explain its rare gastric and bronchoconstrictive adverse effects. However, the recommended single oral dose (100–400 mg) seems to be too low to decrease systemic LT-synthesis in all subjects.