A comparative study on the effects of inhibitors of the lipoxygenase pathway on neutrophil function. Inhibitory effects on neutrophil function may not be attributed to inhibition of the lipoxygenase pathway

The therapeutic effect of fraxetin on ethanol-induced hepatic fibrosis by enhancing ethanol metabolism, inhibiting oxidative stress and modulating inflammatory mediators in rats

The present study was designed to investigate the possible protective effects of fraxetin against ethanol induced liver fibrosis in rats. Rats were underwent intragastric administration of ethanol (5.0-9.5 g/kg) once a day for 24 weeks. Effect of fraxetin against ethanol induced liver fibrosis was investigated by giving 20 or 50 mg/kg fraxetin. At the end of experiment, the livers were collected for histopathological analyses, protein extraction, and enzymatic activities. Our results indicated that fraxetin significantly corrected ethanol-induced hepatic fibrosis, as evidenced by the decrease in serum ALT and AST, the attenuation of histopathological changes. Fraxetin also expedited ethanol metabolism by enhancing the alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) activities. Besides, fraxetin alleviated lipid peroxidation, enhanced hepatic antioxidant capabilities, inhibited CYP2E1 activity, and reduced the inflammatory mediators, including TNF-α and IL-1β via up-regulation of hemeoxygenase-1 (HO-1) protein. In summary, the hepatoprotection of fraxetin is mostly attributed to its antioxidant capability, alcohol metabolism, and anti-inflammation effect.

Influence of coumarin and some coumarin derivatives on serum lipid profiles in carbontetrachloride-exposed rats

In the present study, coumarin and some coumarin derivatives (esculetin, scoparone, and 4-methylumbelliferone) were investigated for their lipid-lowering effect in rats. Male Sprague–Dawley rats (150–200 g) were divided into six groups and each group comprised of five rats. Hepatic injury-dependent hyperlipidemia was induced by carbon tetrachloride (CCl4, 1.25 ml/kg). Coumarin and coumarin derivatives esculetin (35 mg/kg), scoparone (35 mg/kg), 4-methylumbelliferone (35 mg/kg), or coumarin (30 mg/kg) were administered to experimental groups at 12-h intervals. Animals received the derivatives esculetin, scoparone or 4-methylumbelliferone prior to the administration of a single toxic dose of CCl4. Serum total cholesterol (TC), triglyceride (TG), very low-density lipoprotein cholesterol (VLDL-C), and low-density lipoprotein cholesterol (LDL-C) levels significantly increased in CCl4-treated group ( p < 0.05, p < 0.01, p < 0.01, and p < 0.05, respectively), while levels of serum high-density lipoprotein cholesterol (HDL-C) decreased ( p < 0.01). 4-Methylumbelliferone had no recovery effects on serum TC levels, however, significantly prevented CCl4-induced hyperlipidemia by reducing TG and VLDL-C levels ( p < 0.05 and p < 0.05, respectively). In addition, coumarin had no recovery effect on any of the serum lipid parameters against CCl4-induced hyperlipidemia. Among the coumarin derivatives only esculetin and scoparone significantly prevented serum HDL-C in CCl4-induced dyslipidemia. The results from this study indicate that the chemical structure of coumarins plays an important role on the regulation of serum lipid profiles.

Antagonism of human formyl peptide receptor 1 with natural compounds and their synthetic derivatives

Formyl peptide receptor 1 (FPR1) regulates a wide variety of neutrophil functional responses and plays an important role in inflammation and the pathogenesis of various diseases. To date, a variety of natural and synthetic molecules have been identified as FPR1 ligands. Here, we review current knowledge on natural products and natural product-inspired small molecules reported to antagonize and/or inhibit the FPR1-mediated responses. Based on this literature, additional screening of selected commercially available natural compounds for their ability to inhibit fMLF-induced Ca(2+) mobilization in human neutrophils and FPR1 transfected HL-60 cells, and pharmacophore modeling, natural products with potential as FPR1 antagonists are considered and discussed in this review. The identification and characterization of natural products that antagonize FPR1 activity may have potential for the development of novel therapeutics to limit or alter the outcome of inflammatory processes.

NADPH oxidase as a therapeutic target for oxalate induced injury in kidneys

A major role of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase family of enzymes is to catalyze the production of superoxides and other reactive oxygen species (ROS). These ROS, in turn, play a key role as messengers in cell signal transduction and cell cycling, but when they are produced in excess they can lead to oxidative stress (OS). Oxidative stress in the kidneys is now considered a major cause of renal injury and inflammation, giving rise to a variety of pathological disorders. In this review, we discuss the putative role of oxalate in producing oxidative stress via the production of reactive oxygen species by isoforms of NADPH oxidases expressed in different cellular locations of the kidneys. Most renal cells produce ROS, and recent data indicate a direct correlation between upregulated gene expressions of NADPH oxidase, ROS, and inflammation. Renal tissue expression of multiple NADPH oxidase isoforms most likely will impact the future use of different antioxidants and NADPH oxidase inhibitors to minimize OS and renal tissue injury in hyperoxaluria-induced kidney stone disease.

The NADPH oxidase family and its inhibitors

The classical nicotinamide adenine dinucleotide phosphate (NADPH) oxidase was originally detected in neutrophils as a multicomponent enzyme that catalyzes the generation of superoxide from oxygen and the reduced form of NADPH. This enzyme is composed of two membrane-bound subunits (p22phox and gp91phox), three cytosolic subunits (p67phox, p47phox, and p40phox) and a small G-protein Rac (Rac1 and Rac2). Recently, it has been demonstrated that there are several isoforms of nonphagocytic NADPH oxidase. Endothelial cells, vascular smooth muscle cells or adventitial fibroblasts possess multiple isoforms of this enzyme. The new homologs, along with gp91phox are now designated the Nox family of NADPH oxidases and are key sources of reactive oxygen species in the vasculature. Reactive oxygen species play a significant role in regulating endothelial function and vascular tone. However, besides the participation in the processes of physiological cell, these enzymes can also be the perpetrator of oxidative stress that causes endothelial dysfunction. This review summarizes the current state of knowledge of the structure and functions of NADPH oxidase and NADPH oxidase inhibitors in the treatment of disorders with endothelial damage.

Protective effects of coumarin and coumarin derivatives against carbon tetrachloride-induced acute hepatotoxicity in rats

The comparison of the antioxidant activity of some coumarins with their molecular structure is well determined. However, the protective function of coumarins with various chemical structures against liver toxicity has not yet been well established. Therefore, the aim of this study was to evaluate the possible cytoprotective properties of coumarin and some coumarin derivatives against CCl(4) (carbon tetrachloride)-induced hepatotoxicity. Coumarin (1,2-benzopyrone) and coumarin derivatives esculetin (6,7-dihydroxycoumarin), scoparone (6,7-dimethoxycoumarin) and 4-methylumbelliferone (7-hyroxy-4-methyl) were examined for their protective effect against CCl(4)-induced hepatotoxicity in Male Sprague-Dawley rats. A single toxic dose of CCl(4) (1.25 ml kg(-1), orally) produced liver damage in rats, seen histologically as centrilobular necrosis. Administration of CCl(4) increased serum enzyme levels of aspartate transaminase (AST), alanine transaminase (ALT), and alkaline phosphatase (ALP). Pre-treatment of rats with esculetin (31.15 mg kg(-1), orally) and scoparone (35 mg kg(-1), orally) significantly prevented CCl(4)-induced increase in serum enzymes, whereas 4-methylumbelliferone (35 mg kg(-1)) and coumarin (30 mg kg(-1)) had no effect against CCl(4)-induced rise in serum enzymes. Morphological findings were consistent with the plasma transaminase observations. Among the coumarin analogs, esculetin, which possesses orthodihydroxy coumarins, showed the strongest protective effect against CCl(4)-induced liver damage, followed by scoparone, 4-methylumbelliferone and coumarin, respectively. The results of this study indicate that the chemical structures of coumarins play an important role in the prevention of liver toxicity.

Coumarin derivatives protection against ROS production in cellular models of Aβtoxicities

The role of oxidative stress and free radicals in the development of Alzheimer's disease (AD) has been the focus of many recent studies. The role of hydrogen peroxide (H(2)O(2)) in AD is thought to be associated with Abeta (amyloid - beta) damage in cells. A number of coumarin derivatives were previously found to be potent anti-inflammatory and antioxidant agents. Herein, these coumarin derivatives were tested as H(2)O(2) scavengers with the DCF assay using two types of neuronal cells: (a) wild type (N2a) neuroblastoma cells and (b) APP/PS1 transgenic cell line expressing Abeta. Their scavenging activity was varied between the types of cell cultures and it was found to be concentration and time dependent in the mutant cells. Their protective role against cell death further supports this notion. These results suggest that these compounds could be used as a template in the design of new molecules with a possible role in AD.

FcepsilonRI- and Fcgamma receptor-mediated production of reactive oxygen species by mast cells is lipoxygenase- and cyclooxygenase-dependent and NADPH oxidase-independent

We investigated the enzymes responsible for FcepsilonRI-dependent production of reactive oxygen species (ROS) and the influence of ROS on mast cell secretory responses. 5-Lipoxygenase (5-LO) was the primary enzyme involved in ROS production by human mast cells (huMC) and mouse bone marrow-derived mast cells (mBMMC) following FcepsilonRI aggregation because incubation with 5-LO inhibitors (AA861, nordihydroguaiaretic acid, zileuton) but not a flavoenzyme inhibitor (diphenyleneiodonium) completely abrogated Ag-induced dichlorodihydrofluorescein (DCF) fluorescence. Furthermore, 5-LO-deficient mBMMC had greatly reduced FcepsilonRI-dependent DCF fluorescence compared with wild type mBMMC or those lacking a functional NADPH oxidase (i.e., gp91(phox)- or p47(phox)-deficient cells). A minor role for cyclooxygenase (COX)-1 in FcepsilonRI-dependent ROS production was demonstrated by inhibition of Ag-mediated DCF fluorescence by a COX-1 inhibitor (FR122047) and reduced DCF fluorescence in COX-1-deficient mBMMC. Complete abrogation of FcepsilonRI-dependent ROS production in mast cells had no effect on degranulation or cytokine secretion. In response to the NADPH oxidase-stimulating agents including PMA, mBMMC and huMC produced negligible ROS. IgG-coated latex beads did stimulate ROS production in huMC, and in this experiment 5-LO and COX again appeared to be the enzymatic sources of ROS. In contrast, IgG-coated latex bead-induced ROS production in human polymorphonuclear leukocytes occurred by the NADPH oxidase pathway. Thus mBMMC and huMC generate ROS by 5-LO and COX-1 in response to FcepsilonRI aggregation; huMC generate ROS upon exposure to IgG-coated latex beads by 5-LO and COX; and ROS appear to have no significant role in FcepsilonRI-dependent degranulation and cytokine production.

Role of oxylipins and other lipid mediators in fungal pathogenesis

Recently there has been a focused interest in the production of bioactive lipid metabolites from eukaryotic microbes, and in the roles that these molecules play in development and pathological processes. These metabolites have long been known in mammals to be potent modulators of various physiological processes, such as the regulation of inflammation. This area of research has been of particular interest in fungi, where oxylipin production has been correlated with pathogenicity. The aim of this review is to discuss recent findings that show how oxylipins and other lipid mediators affect fungal development, quorum sensing and effecter molecule production, which all amount to a global control by oxylipins of fungal pathogenesis.

Synthesis and Antiinflammatory Activity of Coumarin Derivatives,

The synthesis of several coumarin Mannich bases is described. The structures of the synthesized compounds were confirmed by spectral and elemental analysis. Their lipophilicity was determined experimentally by RPTLC method. All compounds were evaluated for their antiinflammatory and antioxidant activity and for their ability to inhibit in vitro lipoxygenase. The derivatives were found to present antioxidant and antiinflammatory activities. The tested derivatives inhibited carraggeenin-induced hind paw edema. They also significantly suppressed the arthritis induced by Freund's adjuvant. Compound 10, the most active in vivo, was found to possess protective properties against adjuvant-induced arthritis in rats. The biological in vitro activities were concentration dependent. Hydrophilicity, the presence of a free 7-OH, and steric requirements for the substituent at position 8 are the most important factors in terms of SAR. An attempt was made to correlate several physicochemical properties of the molecules with their in vivo/in vitro activity.

Dietary antioxidant compounds and liver health

Chronic liver damage is a widespread pathology characterized by a progressive evolution from steatosis to chronic hepatitis, fibrosis, cirrhosis, and hepatocellular carcinoma. As the oxidative stress plays a central role in liver diseases pathogenesis and progression, the use of antioxidants have been proposed as therapeutic agents, as well as drug coadjuvants, to counteract liver damage. In this work in vitro and in vivo studies, with emphasis on humans and animals experiments, have been considered and reviewed according to antioxidant typologies. Great differences emerge as far as ingested doses, bioavailability and liver ability to accumulate the various compounds. Results available up to now suggest that lycopene-rich foods could be proposed in therapeutic treatment of some liver pathologies. On the other hand contradictory results have been obtained with alpha-tocopherol, beta-carotene and trans-resveratrol. Quercetin, silymarin, esculetin and thyme and rosemary among phenolic compounds need further studies.

Leukotriene B4mediates p47phox phosphorylation and membrane translocation in polyunsaturated fatty acid-stimulated neutrophils

Polyunsaturated fatty acids (PUFAs) and leukotriene B(4) (LTB(4)) are involved in many inflammatory and physiological conditions. The role of arachidonic acid (AA) and linoleic acid (LA) in promoting the assembly of reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase subunits is well known, but the involvement of LTB(4) and other 5-lipoxygenase (5-LO) pathway metabolites of AA in hydrogen peroxide (H(2)O(2)) production by PUFA-stimulated polymorphonuclear leukocytes (PMNs) has not been investigated. We examined this question by determining H(2)O(2) production as well as phosphorylation and membrane translocation of the p47phox subunit of NADPH oxidase. Elicited peritoneal PMNs from rats and from 5-LO-deficient or wild-type mice were pretreated with or without inhibitors of LT biosynthesis and antagonists of the receptors for LTB(4) and cysteinyl LTs for 20 min before stimulation with AA (at 5 and 20 microM) or LA (at 20 microM). PUFAs elicited H(2)O(2) production in a dose-dependent manner, and pharmacologic or genetic inhibition of LT synthesis decreased H(2)O(2) production by approximately 40% when compared with untreated controls. LTB(4) was the moiety responsible for H(2)O(2) production, as revealed by studies using receptor antagonists and its exogenous addition. LTB(4) itself also promoted p47phox phosphorylation and translocation. These results identify a heretofore unrecognized role for activation of 5-LO and subsequent production of LTB(4) in stimulation of PMN NADPH oxidase activation by PUFAs.

Reduction in primary nonfunction of syngeneic islet transplants with nordihydroguaiaretic acid, a lipoxygenase inhibitor

To study the effectiveness of a lipoxygenase inhibitor, nordihydroguaiaretic acid (NDGA), in the reduction of primary nonfunction, an insufficient number of syngeneic islets were transplanted underneath the renal capsule with NDGA administered daily for 4 weeks. After transplantation of the 150 islets, the decrement of blood glucose levels was significantly faster in the mice that had received NDGA than in the mice that had received no drug at all or dimethyl sulfoxide (DMSO) (p < 0.005, p < 0.05). The mean duration of temporary posttransplant hyperglycemia was 22.3 +/- 3.2 (n = 10), 35.9 +/- 2.3 (n = 14), and 33.7 +/- 4.1 (n = 6) days for the respective groups. The diabetic mice that received 300 islets had their blood glucose levels decrease faster than those that received 150 islets (19.7 +/- 1.6 vs. 35.9 +/- 2.3 days, n = 14. p < 0.0001). There was no significant difference in the blood glucose reducing effect between the mice that received 150 islets with NDGA and the mice that received 300 islets [22.3 +/- 3.2 (n = 10) vs. 19.7 +/- 1.6 (n = 14) days, p > 0.05]. The insulin content of the graft from the mice treated with 150 islets and NDGA (3.02 +/- 0.24 microg, n = 4) was higher than that from the mice that received 150 islets but no treatment (1.10 +/- 0.26 microg, n = 15, p < 0.005) or that had been treated with DMSO (1.21 +/- 0.30 microg, n = 4, p <0.05). The insulin content of the pancreas remnant had no significant differences among the three groups. The net glucose-stimulated insulin secretion was 0.82 +/- 0.14 vs. 0.20 +/- 0.10 microIU/islet x 60 min (n = 8, p < 0.005) and 0.59 +/- 0.08 vs. 0.04 +/- 0.02 microIU/islet x 60 min (n = 8, p < 0.0001) for islets cultured without NDGA vs. with NDGA at 1 and 2 weeks, respectively. However, the insulin content of the cultured islets was similar between the two groups for up to 2 weeks of incubation (at 1 week: 0.71 +/- 0.01 vs. 0.67 +/- 0.04 ng/islet, n = 8, p > 0.05; at 2 weeks: 0.71 +/- 0.02 vs. 0.80 +/- 0.07 ng/islet, n = 8, p > 0.05). Serum leukotriene B4 (LTB4) concentrations before and between the fifth and seventh days after transplantation were determined. For diabetic mice that received 150 islets, serum LTB4 levels were 25,835 +/- 3,335 and 27,631 +/- 3,136 pg/ml (n = 4, p > 0.05). For diabetic mice that received 150 islets and NDGA, the corresponding figures were 22,401 +/- 2,706 pg/ml and 27,530 +/- 2,190 pg/ml (n = 8, p > 0.05). The graft histology revealed viable islet cells and networks of close vascular structures around the islets and did not reveal microscopic differences among the samples of all four groups. In conclusion, our data revealed that daily administration of NDGA for 4 weeks enhanced isoislet engraftment and preserved three times more mass of the islet beta cells in the isografts. This result indicates that NDGA reduces primary nonfunction of islet syngeneic grafts in diabetic mice.

Correlation between arachidonic acid oxygenation and luminol-induced chemiluminescence in neutrophils: inhibition by diethyldithiocarbamate

Neutrophils from allergic subjects were hypersensitive to stimulation by low calcium ionophore concentration (0.15 microM), resulting in an increased formation of leukotriene B4 (LTB4), 5S-hydroxy-6,8,11,14-(E,Z,Z,Z)-eicosatetraenoic acid (5-HETE), and other arachidonic acid metabolites through the 5-lipoxygenase pathway. In parallel, luminol-dependent chemiluminescence was also higher in neutrophils from allergic patients at the basal state and after stimulation by calcium ionophore, revealing an enhancement of radical oxygen species and peroxide production. The activity of glutathione peroxidase, the main enzyme responsible for hydroperoxide reduction, was lowered in these cells. Diethyl-dithiocarbamate (DTC) induced a concentration-dependent decrease in chemiluminescence and arachidonic acid metabolism after neutrophil stimulation. These data show that the elevation of arachidonic acid metabolism in neutrophils from allergic patients is strongly correlated with oxidative status. This elevation may be the consequence of an increased cellular hydroperoxide known to activate 5-lipoxygenase (5-LOX) activity and/or an increased arachidonic acid availability, due either to phospholipase A2 (PLA2) activation or inhibition of arachidonate reesterification into phospholipids. Lowering this oxidative status was associated with a concomitant decrease of this metabolism. Our results suggest that the effect of DTC may be the consequence of an inhibition of peroxyl radical and cellular lipid hydroperoxide production. Thus, DTC may modulate arachidonic acid metabolism in neutrophils by modulating the cellular hydroperoxide level.

The adenovirus E3-14.7K protein and the E3-10.4K/14.5K complex of proteins, which independently inhibit tumor necrosis factor (TNF)-induced apoptosis, also independently inhibit TNF-induced release of arachidonic acid

Tumor necrosis factor (TNF) is an inflammatory cytokine that inhibits the replication of many viruses in cultured cells. We have reported that adenovirus (Ad) infection of TNF-resistant mouse cells renders them susceptible to lysis by TNF and that two sets of proteins encoded by the E3 transcription unit block TNF cytolysis. The E3 protein sets are named E3-14.7K (14,700 kDa) and E3-10.4K/14.5K (a complex of two proteins of 10,400 and 14,500 kDa). TNF activation of the 85-kDa cytosolic phospholipase A2 (cPLA2) is thought to be essential for TNF cytolysis (i.e.,TNF-induced apoptosis). Here we provide evidence that cPLA2 is important in the response of Ad-infected cells to TNF and that the mechanism by which E3-14.7K and E3-10.4K/14.5K inhibit TNF cytolysis is by inhibiting TNF activation of cPLA2. cPLA2 cleaves arachidonic acid (AA) specifically from membrane phospholipids; therefore, cPLA2 activity was measured by the release of 3H-AA from cells prelabeled with 3H-AA. Uninfected cells or cells infected with wild-type Ad were not lysed and did not release 3H-AA in response to TNF. In contrast, TNF treatment induced cytolysis and 3H-AA release in uninfected cells sensitized to TNF by treatment with cycloheximide and also in infected cells sensitized to TNF by expression of E1A. In C127 cells, in which either E3-14.7K or E3-10.4K/14.5K inhibits TNF cytolysis, either set of proteins inhibited TNF-induced release of 3H-AA. In C3HA cells, in which E3-14.7K but not E3-10.4K/14.5K prevents TNF cytolysis, E3-14.7K but not E3-10.4K/14.5K prevented TNF-induced release of 3H-AA. When five virus mutants with lesions in E3-14.7K were examined, there was a perfect correlation between a mutant's ability to inhibit both TNF-induced cytolysis and release of 3H-AA. E3-14.7K expressed in two stably transfected C127 cell lines prevented both TNF-cycloheximide-induced cytolysis and release of 3H-AA. The E3 proteins also prevented TNF-induced cytolysis and release of 3H-AA in mouse L929 cells, which are spontaneously sensitive to TNF. TNF cytolysis was blocked by dexamethasone, an inhibitor of PLA2 activity, and by nordihydroquaiaretic acid, which inhibits the metabolism of AA to the leukotrienes. Indomethacin, which blocks the formation of prostaglandins from AA, did not inhibit TNF cytolysis. The leukotrienes and prostaglandins are amplifiers of the inflammatory response. We propose that E3-14.7K and E3-10.4K/14.5K function independently in Ad infection to inhibit both cytolysis and inflammation induced by TNF.

Effects of stilbenes isolated from medicinal plants on arachidonate metabolism and degranulation in human polymorphonuclear leukocytes

Studies were made on the effects of stilbene derivatives isolated from medicinal plants on arachidonate metabolism and degranulation in human polymorphonuclear leukocytes (PMN-L). Resveratrol (3,4',5-trihydroxystilbene) isolated from the roots of Reynoutria japonica was found to inhibit the 5-lipoxygenase products 5-hydroxy-6,8,11,14-eicosatetraenoic acid (5-HETE), 5,12-dihydroxy-6,8,10,14-eicosatetraenoic acid (5,12-diHETE) and leukotriene C4(LTC4); its concentrations for 50% inhibition (IC50) were 8.90 x 10(-6) M, 6.70 x 10(-6) M and 1.37 x 10(-6) M, respectively. The IC50 of 5-HETE, 5,12-diHETE and LTC4 formations of synthetic 3,3',4-trihydroxystilbene were 5.90 x 10(-6) M, 6.30 x 10(-7) M and 8.80 x 10(-7) M, respectively. Moreover, they inhibited the release of lysosomal enzyme such as lysozyme and beta-glucuronidase induced by calcium ionophore A 23187 from human PMN-L at 10(-3)-10(-4) M.

Superoxide scavenging activity in leukocytes and absence of cellular toxicity of a series of coumarins

Sixteen synthetic or plant-derived coumarins of dietary importance with different patterns of substitution were tested for their capacity to scavenge superoxide and for their cytotoxicity. Superoxide was generated by human polymorphonuclear leukocytes stimulated by phorbol myristate acetate and was measured using the reduction of ferricytochrome c or of nitrobule tetrazolium (NBT). Eleven of the coumarins, all lacking dihydroxy substitution, did not scavenge superoxide. Of the remaining five, the most potent scavenger was fraxetin (7,8-dihydroxy-6-methoxycoumarin) with an IC50 (concentration producing 50% inhibition) of 2.3 microM in the cytochrome assay and 5.8 microM using NBT. The other four coumarins (all containing ortho-dihydroxy catechol functions, and found previously to be pro-oxidant in cell-free systems by virtue of reduction of ferric to ferrous ions), themselves rapidly reduced cytochrome c. Therefore their effects on superoxide were measured using NBT, yielding IC50 values in the range 8.5 to 82.0 microM. Fraxetin and the other active and inactive coumarins were not directly cytotoxic at 100 microM to leukocytes or to erythrocytes, as shown by their failure to cause release of cytosolic lactate dehydrogenase or to cause haemolysis, respectively. However, all five dihydroxylated pro-oxidant coumarins were toxic to NS20Y neuroblastoma cells in 24 hr culture, whereas the other eleven coumarins were nontoxic. We conclude that 7,8-dihydroxylated coumarins such as fraxetin are agents which are not themselves directly cytotoxic and are capable of direct scavenging of superoxide anion radicals, an action which might be protective at sites of leukocyte activation during inflammation. However, in the presence of free ferric ions they may exert potentially damaging pro-oxidant actions, including cytotoxicity. This series of compounds provides a useful basis for structure-activity studies designed to achieve separation or combination of these properties.

Ca2+ ionophore A23187-stimulated secretion of azurophil granules in human polymorphonuclear leukocytes is largely mediated by endogenously formed leukotriene B4

The mode of action of the new leukotriene synthesis inhibitor BAY X1005 ((R)-2-[4-(quinolin-2-yl-methoxy)phenyl]-2-cyclopentyl acetic acid) and structurally-related quinoline derivatives is reflected by the binding to a high-affinity binding site presumably identical to FLAP (five lipoxygenase activating protein). In addition to FLAP, we have identified a second BAY X1005 (low-affinity) binding site localized in the granule fraction of human PMNL (polymorphonuclear leukocytes). Based on the hypothesis that the corresponding target protein might be involved in the regulation of granule release, the influence of the leukotriene synthesis inhibitors BAY X1005 and MK-886 and the direct 5-LOX (5-lipoxygenase, EC 1.13.11.34) inhibitor A-64077 on the A23187- and fMLP (N-formyl-methionyl-leucyl-phenylalanine)-stimulated release of beta-glucuronidase (as a marker for azurophil granules) and vitamin B12-binding protein (as a marker for specific granules) was investigated. In contrast to MK-886, neither BAY X1005 nor A-64077 significantly affected fMLP-stimulated granule release. This was also true for the A23187-stimulated release of specific granules; however, under the same conditions the A23187-stimulated release of azurophil granules was almost totally inhibited by all three compounds. No obvious relationship between the corresponding IC50 values and the ability of these compounds to compete for BAY X1005 binding at the low-affinity binding site existed. Instead, by extending these studies to additional inhibitors, a correlation between the IC50 values for inhibition of A23187-stimulated (i) beta-glucuronidase release and (ii) LTB4 (leukotriene B4) synthesis was found (r = 0.969, N = 7). This relationship was independent of the mode of action of the compounds, namely direct 5-LOX inhibition or indirect 5-LOX inhibition mediated via binding to FLAP. These results suggest that 5-LOX metabolites may be involved in A23187-stimulated azurophil granule release. Of the two main biologically active 5-LOX metabolites synthesized under these conditions (LTB4 and 5-hydroxyeicosatetraenoic acid), only LTB4 stimulated beta-glucuronidase release to nearly the same extent as A23187. In addition, this metabolite significantly enhanced A23187-stimulated beta-glucuronidase release, but only at A23187 concentrations (> or = 0.25 mumol/L) which by themselves were not sufficient to trigger LTB4 formation. Moreover, the inhibition of A23187-stimulated beta-glucuronidase release by BAY X1005 or A-64077 was totally reversed by the addition of LTB4.(ABSTRACT TRUNCATED AT 400 WORDS)

In-vitro evaluation of 5-lipoxygenase and cyclo-oxygenase inhibitors using bovine neutrophils and platelets and HPLC

Inhibition of 5-lipoxygenase has been determined by monitoring the formation of leukotriene B4 and 5-hydroxyeicosatetraenoic acid in bovine polymorphonuclear leucocytes. For evaluating the inhibition of cyclo-oxygenase two different test systems are presented: the first uses 12-hydroxyheptadecatrienoic acid produced by bovine platelets as an indicator of the cyclo-oxygenase activity; the second test system monitors the prostaglandin E2 formation by bovine platelets. All arachidonic acid metabolites are quantified by reverse-phase HPLC with UV-detection.

Interactions of a series of coumarins with reactive oxygen species. Scavenging of superoxide, hypochlorous acid and hydroxyl radicals

Sixteen plant-derived or synthetic coumarins with various hydroxyl and other substitutions were tested for their ability to inhibit lipid peroxidation and to scavenge hydroxyl radicals, superoxide radicals and hypochlorous acid. Seven unsubstituted or monosubstituted coumarins were essentially inactive in all tests except for ability to scavenge OH with rate constants approximately greater than 1 x 10(9) M-1. sec-1. Of the remaining nine, six containing dihydroxy substitutions were effective inhibitors of Fe3+-ascorbate-dependent microsomal lipid peroxidation (IC50 less than 20 microM), with ortho-dihydroxy + one additional substitution optimal (IC50 less than 10 microM). ortho-Dihydroxylated coumarins were pro-oxidant (enhanced OH generation) in the Fe3+-EDTA-H2O2 deoxyribose system but decreased OH' generation in the Fe3+-ascorbate-H2O2 deoxyribose system, indicating that these compounds can both chelate iron ions and also readily donate electrons for redox cycling of Fe3+. The meta-dihydroxycoumarin did not show this behaviour, but was an effective scavenger of hypochlorous acid, a property shared by only one other compound. Several other coumarins with one or more hydroxyl substituents were also capable of effectively removing superoxide anions (IC50 3.7-72 microM), although some could not be quantified due to direct rapid reduction of cytochrome c. We conclude that several compounds, notably 5,7-dihydroxy-4-methylcoumarin, possess beneficial biochemical profiles of interest in relation to pathophysiological processes dependent upon reactive oxygen species.

5-lipoxygenase inhibitors and their anti-inflammatory activities

A wide variety of agents have been reported as 5-LO inhibitors. The majority of the series appear to be lipophilic reducing agents, including phenols, partially saturated aromatics, and compounds containing heteroatom-heteroatom bonds. Many of these are not selective 5-LO inhibitors, but often affect CO and other LOs as well. In vivo systemic activity for many of these has been, in general, disappointing, probably because of poor bioavailability caused by lipophilicity and metabolic instability (oxidation, and conjugation of phenolic compounds). However, topically a number of agents have shown promise for skin inflammation, with Syntex's lonapalene the most advanced of these. Most results published to date appear more disappointing in the allergy/asthma field. More excitingly, a few structural types are selective 5-LO inhibitors which have shown systemic activity in vivo and in the clinic. Abbott's zileuton (136) appears to be one of the leading compounds in this category, along with other hydroxamates such as BW-A4C (129) from Burroughs-Wellcome. Recent selective non-reducing agents such as Wyeth-Ayerst's Wy-50,295 (143) and the similar ICI compounds such as ICI 216800 (145) also hold promise. The enantiospecific effects of (106) and (145) are especially interesting for the design of new inhibitors. If compounds like these validate the hypothesis that inhibition of 5-LO will have a significant anti-inflammatory effect, a redoubling of effort throughout the industry to find second- and third-generation selective agents may be expected. Part of the difficulty in interpreting and comparing the 5-LO literature is the plethora of test methods and activity criteria. As pointed out in the introduction, inhibition of product release from cells, often stimulated with A23187, has commonly been used to demonstrate 5-LO inhibition. However, this type of assay cannot be assumed to be diagnostic for 5-LO inhibition. Only if specificity for 5-LO product generation and (ideally) activity in cell-free enzymes is also shown should mechanistic interpretations be made. Recently, a new class of compounds was found at Merck which inhibited LT biosynthesis without inhibiting 5-LO, but apparently by a novel, specific mechanism. L-655,240 (169) and L-663,536 (MK-886) (170) were both active in human ISN, with IC50 values in the low micromolar range. Both also orally inhibited GPB (< 1 mg/kg). MK-886 was effective in Ascaris-induced asthma in squirrel monkeys, in rat carrageenan pleurisy, in rat Arthus pleurisy, and (topically) in guinea-pig ear oedema induced by A23187.(ABSTRACT TRUNCATED AT 400 WORDS)

Inhibition of 5-lipoxygenase product formation and polymorphonuclear cell degranulation by tenidap sodium in patients with rheumatoid arthritis

We studied the effect of tenidap sodium, a new antiinflammatory/antirheumatic drug (120 mg/day for 7 days), on eicosanoid production and neutrophil degranulation in patients with rheumatoid arthritis. Endogenous prostaglandin E2 levels and ex vivo production of leukotriene B4 (LTB4) were measured in synovial fluid samples obtained at baseline and 1 week later. We measured peripheral blood polymorphonuclear cell (PMN) degranulation following surface-bound IgG stimulation, a possible 5-lipoxygenase product-mediated event, by determining lactoferrin and elastase release into the culture fluid. We found decreased levels of endogenous prostaglandin E2 as measured by radioimmunoassay, and decreased ex vivo production of LTB4 by PMN as measured by high performance liquid chromatography, in synovial fluid samples from patients who took tenidap. Release of the granule proteins lactoferrin and elastase was decreased in PMN obtained from patients receiving tenidap, as well as in the PMN incubated in vitro with tenidap. Improvement in clinical measures paralleled the biochemical changes. The unique 5-lipoxygenase inhibitory property of tenidap, as measured by LTB4 production and degranulation, suggests that it may have clinical activity which differentiates it from nonsteroidal antiinflammatory drugs.

Inhibition of leukotriene biosynthesis and polymorphonuclear leukocyte functions by orally active quinolylmethoxyphenylamines

The N-substituted quinolylmethoxyphenylamines, ETH603, ETH615 and ETH647, inhibited the formation of LTB4 in rat peritoneal leukocytes, human peripheral polymorphonuclear leukocytes and canine whole blood. In rat and human cells, the compounds also inhibited the formation of 5-HETE and stimulated the synthesis of 15-HETE. In rat leukocytes, the compounds were 15-30 times more potent inhibitors of LTB4 synthesis than nordihydroguaiaretic acid, but in canine whole blood they were significantly less potent, possibly due to protein binding. However, after oral administration of the compounds to dogs a long-lasting inhibition of LTB4 production in peripheral blood was observed at serum concentrations much lower than those required in vitro. Furthermore, the compounds inhibited the LTB4-directed chemotaxis and the phagocytosis of C. albicans blastospores by canine polymorphonuclear leukocytes both in vitro and following oral administration. The calcium ionophore A23187-induced release of LTB4 in the peritoneal cavity of rats was also inhibited by systemic administration of the compounds. We therefore conclude that these novel quinolines are orally active 5-lipoxygenase inhibitors which may accumulate in inflammatory cells in vivo, leading to potent inhibition of leukotriene biosynthesis and cell function.

Antiinflammatory effects of various drugs on acetic acid induced colitis in the rat

The efficacy of various drugs used to treat ulcerative colitis, (sulfasalazine, 5-aminosalicylate, hydrocortisone) was investigated in a model of acetic acid-induced colitis in the rat. Subsequently, we tested the ability of antioxidant/5-lipoxygenase inhibitors (gossypol and nordihydroguiaretic acid [NDGA]) and a cyclooxygenase inhibitor (indomethacin) to attenuate the macroscopic colonic damage and/or neutrophil influx (myeloperoxidase activity [MPO]) associated with this model of colitis. Oral pretreatment with either sulfasalazine, gossypol, or NDGA significantly decreased colonic MPO activity induced by acetic acid. Intrarectal administration of such drugs resulted in an even larger reduction of the colonic inflammation, with gossypol being the most potent compound. Oral or intrarectal administration of corticosteroids (dexamethasone, hydrocortisone) also attenuated the parameters of acetic acid induced colitis. In contrast, pretreatment with indomethacin was ineffective, or when administered daily after colitis induction, indomethacin actually increased colonic neutrophil influx significantly. Our data suggest that both the route of drug administration and dosing regimen employed affect the antiinflammatory potency and/or efficacy of compounds on colitis induced by acetic acid in the rat. Drugs which were effective against this colitis may act by scavenging of oxygen derived free radicals.

Activation of the respiratory burst oxidase in neutrophils: on the role of membrane-derived second messengers, Ca++, and protein kinase C

A major bactericidal mechanism of neutrophils involves activation of the respiratory burst oxidase to generate superoxide (O2-). The oxidase is activated rapidly, often within a minute, in response to extracellular signals such as chemoattractants, inflammatory mediators, and invading microorganisms. Increasing evidence indicates that lipases also respond rapidly, releasing potent regulatory molecules from progenitor lipids. Released molecules include potential regulators of protein kinase C--diacylglycerol (DAG), arachidonate, and sphingosine--and levels of one of these, DAG, frequently correlate with O2- production. In this author's view, the available data implicate DAG and protein kinase C as key factors in the regulation of the respiratory burst. Herein, the array of activating agonists, the generation and function of some lipid-derived mediators, and evidence pertaining to the participation of protein kinase C are reviewed.

Effect of the 5-lipoxygenase inhibitor piriprost on superoxide production by human neutrophils

The effect of 6,9-deepoxy-6,9-(phenylimino)-delta 6,8-prostaglandin I1 (Piriprost) on the oxidative response was studied in human neutrophils stimulated by N-formyl-methionyl-leucyl-phenylalanine (fMLP), phorbol 12-myristate, 13-acetate (PMA) or opsonized zymosan. Piriprost inhibited the stimulatory effect of fMLP on superoxide anion (O2-) generation, at concentrations higher than those which depress leukotriene B4 (LTB4) formation. This inhibition was overcome by increasing the concentration of fMLP. Neither exogenous LTB4 nor indomethacin were able to reverse the inhibitory effect of piriprost on fMLP action. In contrast, piriprost did not inhibit the stimulation of O2- production induced by PMA or zymosan. Piriprost behaves thus as a specific and apparently competitive antagonist of fMLP: this action does not seem to involve lipoxygenase inhibition and might be exerted at the level of the fMLP receptor or its associated mechanisms of transduction.

Effect of recombinant DNA-produced tumor necrosis factor on various parameters of neutrophil function

The effect of recombinant DNA-produced human tumor necrosis factor (TNF) on various parameters of neutrophil function was evaluated. TNF was a weak direct activator of oxygen radical production. It released the specific granule contents to a limited extent, but the azurophilic granule contents were retained even in the presence of cytochalasin B. It had a chemotactic activity for neutrophils, as determined by the use of a modified Boyden's chamber. Pretreatment of neutrophils with TNF increased phagocytosis of opsonized particles and markedly potentiated in a dose-dependent manner oxygen radical production induced by opsonized zymosan. The inhibitors of lipoxygenase, but not those of cyclooxygenase, reduced the potentiating effect of TNF on phagocytosis, suggesting that the products of lipoxygenase play an important role in mediating the effect of TNF on neutrophils.

The suppression of granulocyte functions by lipophilic antioxidants

The effects of several antioxidants on the three major functions of human neutrophils--oxidative burst, secretion and leukotriene formation--were investigated with special emphasis on the lipophilicity. The most striking differences were obtained when ascorbate and the lipophilic ester ascorbyl palmitate were compared. As expected, the luminol- and lucigenin-dependent chemiluminescence was inhibited by all antioxidants to a different degree. Ascorbyl palmitate was able to block the biphasic luminol-dependent response completely with IC50 values of 10 and 25 microM for the first and second phase, respectively. In contrast, ascorbate only blocked efficiently the first phase of the response. The secretion of elastase was inhibited by ascorbyl palmitate dose-dependently with an IC50 value of around 200 microM, whereas ascorbate was completely inactive. Electron microscopy supported the assumption that inhibition was due to a block in degranulation and not to enzyme inactivation. This was further supported by a parallel, although somewhat lower, inhibition of other secretory enzymes like myeloperoxidase, beta-glucuronidase or lysozyme. Cells treated with the Ca2+-ionophore A23187 responded by LTB4-synthesis which was also inhibited by ascorbyl palmitate. A very efficient inhibition was observed in cell homogenates with an IC50 value of 1.5 microM. No inhibition by ascorbate was detected in both systems. Concomitant with the inhibition of 5-lipoxygenase the activity of 15-lipoxygenase increased. We conclude that cellular reductants may control neutrophil functions and that the inhibition by ascorbyl palmitate of the three processes relevant for inflammatory responses could be of therapeutic importance.

Injury to endothelial cells by phagocytosing polymorphonuclear leukocytes and modulatory role of lipoxygenase products

Phagocytosis of microorganisms by polymorphonuclear leukocytes (PMN) is accompanied by inadvertent extracellular release of microbicidal products; this could result in tissue damage. We investigated whether PMN damages endothelial cells when phagocytosis of Staphylococcus aureus occurs on the endothelial surface and how this damage might be modulated. Damage was assayed by the measurement of cell detachment or cell lysis of cultured endothelial cells that were radiolabeled with 51Cr. Uptake of bacteria was accompanied by nonlytic detachment of endothelial cells from the monolayer. This effect was inhibited by alpha-1-antitrypsin but remained unaffected by scavengers of toxic oxygen species. During phagocytosis, PMN adhered to the endothelial cells. Adherence could be prevented by inhibition of the lipoxygenase pathway of arachidonic acid metabolism of the PMN with nordihydroguaiaretic acid. This inhibition also resulted in a marked decrease of the detaching activity of the PMN. The addition of exogenous leukotriene B4 during phagocytosis greatly enhanced the damage to the endothelial monolayer. These results indicate that phagocytosis of staphylococci by PMN is accompanied by injury to endothelial cell monolayers due to released lysosomal proteases and that products of the lipoxygenase pathway of PMN play a modulatory role in this injury.