MK886, a potent and specific leukotriene biosynthesis inhibitor blocks and reverses the membrane association of 5-lipoxygenase in ionophore-challenged leukocytes.
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Recently, we have shown that ionophore activation of human leukocytes results in leukotriene synthesis and a translocation of 5-lipoxygenase from the cytosol to cellular membrane. This membrane translocation was postulated to be an important early activation step for the enzyme. 3-[1-(p-Chlorobenzyl)-5-(isopropyl)-3-tert-butylthioindol-2-yl]-2, 2- dimethylpropanoic acid (MK886) is a potent and specific inhibitor of leukotriene biosynthesis in vivo and in intact cells, but has no direct effect on 5-lipoxygenase activity in cell-free systems. In this report, we show that MK886 can both prevent and reverse the membrane translocation of 5-lipoxygenase, in conjunction with the inhibition of leukotriene synthesis. Similar compounds of the indole class could also inhibit the membrane translocation of 5-lipoxygenase in a rank order of potency that correlated with their potencies for leukotriene synthesis inhibition. In contrast L-656,224, a direct 5-lipoxygenase inhibitor, had no effect on the translocation of the enzyme. Attempts to demonstrate the effects of MK886 on the association of 5-lipoxygenase with membrane in cell-free preparations failed due to a nonspecific Ca2+-dependent sedimentation of the enzyme. The mechanism of action of MK-886 is therefore to block translocation, prevent subsequent activation of 5-lipoxygenase, and hence block cellular leukotriene biosynthesis. (+info)
Dietary supplementation with oils rich in (n-3) and (n-6) fatty acids influences in vivo levels of epidermal lipoxygenase products in guinea pigs.
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Certain dietary oils may have therapeutic potential in the treatment of inflammatory skin disorders. Presumably, the fatty acid constituents of these dietary oils exert their effects by altering the levels of cutaneous eicosanoids. Prompted by this possibility, we investigated whether supplementation of guinea pig diets with fish oil [rich in 20:5(n-3)] or borage oil [rich in 18:3(n-6)] could significantly alter epidermal levels of eicosanoids compared with control animals supplemented with olive oil. After feeding periods of 4, 8 or 12 wk, the epidermis from the animals was analyzed for: 1) fatty acid composition of individual epidermal phospholipids, 2) levels of lipoxygenase products, and 3) levels of cyclooxygenase products (prostaglandins). Our results demonstrated that the animals supplemented with dietary fish oil had elevated levels of 20:5(n-3) in epidermal phospholipids and elevated epidermal levels of 15-hydroxyeicosapentaenoic acid (15-HEPE) [the 15-lipoxygenase product of 20:5(n-3)] compared with guinea pigs fed olive oil or borage oil. Similarly, the animals supplemented with dietary borage oil had elevated levels of 20:3(n-6) [the epidermal elongase product of 18:3(n-6)] in epidermal phospholipids and elevated epidermal levels of 15-hydroxyeicosatrienoic acid [15-HETrE, the epidermal 15-lipoxygenase product of 20:3(n-6)] compared with guinea pigs fed olive oil or fish body oil. There were no significant changes in epidermal levels of prostaglandins. Both 15-HEPE and 15-HETrE have been identified as possible anti-inflammatory metabolites, and their elevated presence in the epidermis of animals fed oils rich in 20:5(n-3) or 18:3(n-6) may provide a mechanism for the beneficial effects of these oils on inflammatory conditions. (+info)
Evidence for cytokine regulation of cholesterol metabolism in herpesvirus-infected arterial cells by the lipoxygenase pathway.
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Cytokines such as tumor necrosis factor (TNF), interleukin-1 (IL-1), and gamma-interferon (IF) are produced by activated hematopoietic cells. They possess antiviral activity and have other biological activities such as induction of cell proliferation and hemorrhagic necrosis of tumors. Since herpes simplex virus (HSV) infection of human vascular cells is known to produce a biochemical and cytopathological effect virtually indistinguishable from atherosclerosis, we hypothesized that these cytokines many prevent cholesteryl ester (CE) accumulation in arterial smooth muscle cells (SMC) that is seen with herpesvirus infection. We now report that TNF and IL-1 but not gamma-IF prevent CE accumulation in HSV-infected arterial SMC by induction of cyclic AMP-dependent CE hydrolysis. This effect is mediated through the arachidonate 12-lipoxygenase pathway via 12-HETE since pretreatment of cells with several lipoxygenase inhibitors abolishes the antiviral effect and 12-HETE is the major (greater than 99%) lipoxygenase metabolite produced by these cells. This conclusion is further based on our observations that TNF and IL-1 enhance 12-HETE production in SMC and that 12-HETE significantly increases both intracellular cyclic AMP and lysosomal CE hydrolysis. Moreover, dibutyryl cyclic AMP restored a normal phenotype in these virally infected cells. Collectively, these findings identify for the first time a biochemical mechanism involved in the reduction of lipid accumulation in virally infected arterial SMC by these potent cytokines. (+info)
2-substituted indazolinones: orally active and selective 5-lipoxygenase inhibitors with anti-inflammatory activity.
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1. This paper describes the pharmacological profile of ICI207968, a novel, orally-active and selective inhibitor of 5-lipoxygenase. 2. Inhibition of leukotriene B4 (LTB4) synthesis by 2-substituted indazolinones was not directly related to redox potential but was critically dependent on the nature of the N2 substituent. 2-(3-Pyridylmethyl)-indazolinone (ICI207968) combined selectivity and oral potency. 3. In several in vitro systems ICI207968 exhibited similar lipoxygenase inhibitory potency (IC50 values from 1.5 microM to 6.0 microM) and was approximately 300 times less potent against cyclo-oxygenase, as measured by inhibition of prostaglandin E2 (PGE2) synthesis. 4. ICI207968 also produced selective lipoxygenase inhibition following oral administration in the rat. ED50 values of 2.5, 10 and 25 mg kg-1 p.o. for inhibition of LTB4 release from A23187-stimulated blood were obtained 1, 3 and 5 h after dosing. The compound did not inhibit PGE2 synthesis at oral doses up to 300 mg kg-1. 5. Co-administration of ICI207968 with arachidonic acid, into rabbit dermis, potently inhibited both plasma extravasation and polymorphonuclear leucocyte (PMNL) infiltration induced by this inflammatory fatty acid. The anti-inflammatory potency of a number of intradermally administered indazolinones, with similar redox potentials, was related to their inhibitory potency against leukotriene generation in blood. Oral administration of ICI207968 (100 mg kg-1) in the rabbit inhibited ex vivo leukotriene generation in blood and arachidonic acid-induced skin inflammation. 6. These data demonstrate that ICI207968 is an orally active and selective inhibitor of 5-lipoxygenase which has anti-inflammatory properties. IC1207968 will be a valuable agent for clarifying the biological roles of leukotrienes and the therapeutic potential of 5-lipoxygenase inhibitors. (+info)
Role of arachidonic acid lipoxygenase metabolites in acetylcholine-induced relaxations of mouse arteries.
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