5-lipoxygenase inhibitors and their anti-inflammatory activities

Dehydrodieugenol B and hexane extract from Endlicheria paniculata regulate inflammation, angiogenesis, and collagen deposition induced by a murine sponge model

The present study reports the evaluation of hexane extract from Endlicheria paniculata and its main metabolite dehydrodieugenol B in the inflammatory response induced by a murine implant sponge model. As a result, a reduction in the inflammatory markers (myeloperoxidase and N-acetyl-β-D-glucosaminidase) and number of mast cells were observed in comparison to the control group. All doses were also able to reduce angiogenic parameters evaluated in fibrovascular tissue. In implants treated with dehydrodieugenol B a reduction in total collagen deposition and types I and III collagen fibers were observed, while an increased in total collagen deposition and types I and III collagen fibers were observed in the treatment with hexane extract. Docking studies into cyclooxygenase-2 active site revealed that the dehydrodieugenol B had binding modes and energies comparable with celecoxib, diclofenac and ibuprofen. Therefore, dehydrodieugenol B was able to alter key components of chronic inflammation, resulting in a reduced inflammatory response and also presenting antifibrogenic and antiangiogenic effects. However, treatment with hexane extract resulted in a reduced inflammatory response with antiangiogenic effects, but caused fibrogenic effects.

Current Advances in the Synthesis and Biological Evaluation of Pharmacologically Relevant 1,2,4,5-Tetrasubstituted-1H-Imidazole Derivatives

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In recent years, the synthesis and evaluation of the biological properties of 1,2,4,5-tetrasubstituted-1H-imidazole derivatives have been the subject of a large number of studies by academia and industry. In these studies it has been shown that this large and highly differentiated class of heteroarene derivatives includes high valuable compounds having important biological and pharmacological properties such as antibacterial, antifungal, anthelmintic, anti-inflammatory, anticancer, antiviral, antihypertensive, cholesterol-lowering, antifibrotic, antiuricemic, antidiabetic, antileishmanial and antiulcer activities.

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The present review with 411 references, in which we focused on the literature data published mainly from 2011 to 2017, aims to update the readers on the recent developments on the synthesis and biological evaluation of pharmacologically relevant 1,2,4,5-tetrasubstituted-1H-imidazole derivatives with an emphasis on their different molecular targets and their potential use as drugs to treat various types of diseases. Reference was also made to substantial literature data acquired before 2011 in this burgeoning research area.

Inhibition of 5-lipoxygenase triggers apoptosis in pancreatic cancer cells

The 5-lipoxygenase (5-LOX) pathway has been associated with a variety of inflammatory diseases including asthma, atherosclerosis, rheumatoid arthritis, cancer and liver fibrosis. Several classes of 5-LOX inhibitors have been identified, but only one drug, zileuton, a redox inhibitor of 5-LOX, has been approved for clinical use. In the present study, 5-LOX was found to be overexpressed not only in pancreatic cancer cell lines but also in tissue samples of patients suffering from pancreatic adenocarcinoma. There was a close correlation between the tumor expression levels of 5-LOX mRNA and protein and the clinicopathological patient characteristics including lymph node metastasis and TNM stage. Zileuton suppressed the proliferation of SW1990 cells in a concentration- and time‑dependent manner. In addition, zileuton induced SW1990 cells to undergo apoptosis and significantly decreased 5-LOX expression. The number of apoptotic cells, estimated by flow cytometry, Annexin V/PI assay, TUNEL staining and sub‑diploid population was significantly higher than that of the control. These results suggest that the level of 5-LOX expression was increased in pancreatic cancer tissues and may be related to lymph node metastasis and TNM stage.

Aryl-acetic and cinnamic acids as lipoxygenase inhibitors with antioxidant, anti-inflammatory, and anticancer activity

Cinnamic acids have been identified as interesting compounds with cytotoxic, anti-inflammatory, and antioxidant properties. Lipoxygenase pathway, catalyzing the first two steps of the transformation of arachidonic acid into leukotrienes is implicated in several processes such as cell differentiation, inflammation and carcinogenesis. Development of drugs that interfere with the formation or effects of these metabolites would be important for the treatment of various diseases like asthma, psoriasis, ulcerative colitis, rheumatoid arthritis, atherosclerosis, cancer, and blood vessel disorders. Till now, asthma consists of the only pathological case in which improvement has been shown by lipoxygenase LO inhibitors. Thus, the research has been directed towards the development of drugs that interfere with the formation of leukotrienes. In order to explore the anti-inflammatory and cytotoxic effects of antioxidant acrylic/cinnamic acids a series of derivatives bearing the appropriate moieties have been synthesized via the Knoevenagel condensation and evaluated for their biological activities. The compounds have shown important antioxidant activity, anti-inflammatory activity and very good inhibition of soybean lipoxygenase while some of them were tested for their anticancer activity.

Role of cysteinyl-leukotrienes for portal pressure regulation and liver damage in cholestatic rat livers

Kupffer cells (KCs) have a major role in liver injury, and cysteinyl-leukotrienes (Cys-LTs) are known to be involved as well. The KC-mediated pathways for the production and secretion of Cys-LT in cholestatic liver injury have not yet been elucidated. Here, we hypothesized that KC activation by Toll-like receptor ligands results in Cys-LT-mediated microcirculatory alterations and liver injury in acute cholestasis. We hypothesized further that this situation is associated with changes in the secretion and production of Cys-LT. One week after bile duct ligation (BDL), livers showed typical histological signs of cholestatic liver injury. Associated microcirculatory disturbances caused increased basal and maximal portal pressure following KC activation. These differences were determined in BDL livers compared with sham-operated livers in vivo (KC activation by LPS 4 mg/kg b.w.) and in isolated perfused organs (KC activation by Zymosan A, 150 μg/ml). Treatment with the 5-lipoxygenase inhibitor MK-886 alone did not alter portal perfusion pressure, lactate dehydrogenase (LDH) efflux, or bile duct proliferation in BDL animals. Following KC activation, portal perfusion pressure increased. The degree of cell injury was attenuated by MK-886 (3 μM) treatment as estimated by LDH efflux. In normal rats, a large amount of Cys-LT efflux was found in the bile. Only a minor amount was found in the effluent perfusate. In BDL livers, the KC-mediated Cys-LT efflux into the sinusoidal system increased, although the absolute Cys-LT level was still grossly lower than the biliary excretion in sham-operated livers. In conclusion, our results indicate that treatment with Cys-LT inhibitors might be a relevant target for attenuating cholestatic liver damage.

Inhibition of Experimental Systemic Inflammation (Septic Inflammation) and Chronic Bronchitis by New Phytoformula BL Containing Broussonetia papyrifera and Lonicera japonica

Broussonetia papyrifera and Lonicera japonica have long been used in the treatment of inflammatory disorders in Chinese medicine, especially respiratory inflammation. Previously, a new phytoformula (BL) containing B. papyrifera and L. japonica was found to exert strong anti-inflammatory activity against several animal models of inflammation, especially against an animal model of acute bronchitis. In the present investigation, the effects of BL on animal models of septic inflammation and chronic bronchitis are examined. Against lipopolysaccharide (LPS)-induced septic inflammation in mice, BL (200-400 mg/kg) reduced the induction of some important proinflammatory cytokines. At 1 h after LPS treatment, BL was found to considerably inhibit TNF-α production when measured by cytokine array. At 3 h after LPS treatment, BL inhibited the induction of several proinflammatory cytokines, including IFN-γ and IL-1β, although dexamethasone, which was used as a reference, showed a higher inhibitory action on these biomarkers. Against chronic bronchitis induced by LPS/elastase instillation in rats for 4 weeks, BL (200-400 mg/kg/day) significantly inhibited cell recruitment in bronchoalveolar lavage fluid. Furthermore, BL considerably reduced lung injury, as revealed by histological observation. Taken together, these results indicate that BL may have a potential to treat systemic septic inflammation as well as chronic bronchitis.

Regulation of leukotriene and 5oxoETE synthesis and the effect of 5-lipoxygenase inhibitors: a mathematical modeling approach

BACKGROUND

5-lipoxygenase (5-LO) is a key enzyme in the synthesis of leukotrienes and 5-Oxo-6E,8Z,11Z,14Z-eicosatetraenoic acid (oxoETE). These inflammatory signaling molecules play a role in the pathology of asthma and so 5-LO inhibition is a promising target for asthma therapy. The 5-LO redox inhibitor zileuton (Zyflo IR/CR(®)) is currently marketed for the treatment of asthma in adults and children, but widespread use of zileuton is limited by its efficacy/safety profile, potentially related to its redox characteristics. Thus, a quantitative, mechanistic description of its functioning may be useful for development of improved anti-inflammatory targeting this mechanism.

RESULTS

A mathematical model describing the operation of 5-LO, phospholipase A2, glutathione peroxidase and 5-hydroxyeicosanoid dehydrogenase was developed. The catalytic cycles of the enzymes were reconstructed and kinetic parameters estimated on the basis of available experimental data. The final model describes each stage of cys-leukotriene biosynthesis and the reactions involved in oxoETE production. Regulation of these processes by substrates (phospholipid concentration) and intracellular redox state (concentrations of reduced glutathione, glutathione (GSH), and lipid peroxide) were taken into account. The model enabled us to reveal differences between redox and non-redox 5-LO inhibitors under conditions of oxidative stress. Despite both redox and non-redox inhibitors suppressing leukotriene A4 (LTA4) synthesis, redox inhibitors are predicted to increase oxoETE production, thus compromising efficacy. This phenomena can be explained in terms of the pseudo-peroxidase activity of 5-LO and the ability of lipid peroxides to transform 5-LO into its active form even in the presence of redox inhibitors.

CONCLUSIONS

The mathematical model developed described quantitatively different mechanisms of 5-LO inhibition and simulations revealed differences between the potential therapeutic outcomes for these mechanisms.

Is there a role for leukotriene antagonists in the prevention of recurrent nasal polyps?

PURPOSE OF REVIEW

The aim of this review is to provide the current available data for leukotriene receptor antagonists in the treatment of nasal polyps, the use in the postoperative therapy single or as an add-on to standard treatments.

RECENT FINDINGS

Surgical treatment of nasal polyps was refined in the last 30 years by the introduction of functional endoscopic sinus surgery and nasal endoscopy for monitoring nasal polyp patients. As the relapse is the main challenge and as nasal steroids only delay it, a more efficient treatment is needed. Leukotriene antagonists have effects on asthma and allergic rhinitis; preliminary data show some benefits in nasal polyps.

SUMMARY

In the surgery of nasal polyps, recurrence is the main problem. Steroids are the current standard therapy, but the limitations are obvious. The role of leukotrienes in the disorder of nasal polyps is well established now, and with the antagonists available, interest rose in treating nasal polyps. A total of 356 patients took part in several studies involving leukotriene antagonists in the nasal polyp population. Some studies have minor levels of evidence; the data show positive effects for patients in preoperative and postoperative studies and medical treatments. There were benefits as an add-on to steroids and data from allergic rhinitis studies also show possible synergism with antihistamines. There are hints for a positive effect on eosinophil inflammation, clinical symptom scores, nasal airflow, sneezing and postnasal drip. Although some effects are shown, more controlled studies are necessary for reliable data.

Lipoxygenase inhibitors: a comparative QSAR study review and evaluation of new QSARs

This paper contains a quantitative structure activity relationship (QSAR) study for lipoxygenase (LO) inhibitors. It reveals that in almost all cases, the clog P parameter plays an important part in the QSARs (linear or bilinear model). In some cases the steric factors such as the overall molar refractivity (CMR) or the substituents molar refractivity (MR) (linear or parabola) are important. Electronic effects are comparatively unimportant. The study shows that log P as calculated from the Clog P program is suitable for this form of QSAR study.

Action of cyclooxygenase inhibitors and a leukotriene biosynthesis inhibitor on cisplatin-induced acute and delayed emesis in the ferret

Cisplatin at 5 mg/kg, i.p. induced an acute (day 1) and delayed (days 2 and 3) emetic response in the ferret that was used to investigate the anti-emetic activity of the non-selective cyclooxygenase inhibitor indomethacin (3 - 30 mg/kg, i.p., three times per day) and two cyclooxygenase-2 inhibitors, DFU [5,5-dimethyl-3-(3-fluorophenyl)-4-(4-methylsulphonyl)phenyl-2(5H)-furanone; 1 - 10 mg/kg, i.p. administered at 40 and 48 h] and L-745,337 [5-methanesulphonamido-6-(2,4-diflurothiophenyl)-1-indanone; 10 mg/kg, i.p., administered at 40 and 48 h]. Only indomethacin potentiated significantly cisplatin-induced retching + vomiting (P<0.05); DFU antagonized delayed emesis (P<0.05) but the action was not dose-related and L-745,337 was inactive (P>0.05). However, indomethacin alone (30 mg/kg) also induced emesis (P<0.05). The leukotriene biosynthesis inhibitor, MK-886 {3-[1-(p-chlorobenzyl)-5-(isopropyl)-3-tert-butylthioindol-2-yl]-2,2-dimethylpropanoic acid; 1 - 10 mg/kg, i.p., three times per day} had no action to modify cisplatin-induced emesis (P>0.05). The combination treatment of indomethacin (10 mg/kg, i.p., three times per day) with MK-886 (10 mg/kg, i.p., three times per day) did not antagonize cisplatin-induced acute delayed retching + vomiting and had a different profile compared to the action of dexamethasone (1 mg/kg, i.p., three times per day; P<0.05). Inhibition of the cyclooxygenase and lipoxygenase pathways does not account for the anti-emetic of dexamethasone.

The emerging role of leukotriene modifiers in allergic rhinitis

Leukotriene modifiers have been shown to be efficacious in the treatment of asthma. Because of this success, and the fact that leukotrienes can be recovered not only from bronchoalveolar lavage fluid but also nasal lavage fluid, some researchers have suggested that these medications may also be useful for treating allergic rhinitis. Because the upper and lower airways are linked physically, there has been an assumption that therapy for upper and lower airway disease should be similar. This critical appraisal examines available data both supporting and refuting the emerging role of leukotriene modifiers in the treatment of allergic rhinitis. Although many studies have shown an improvement in nasal symptoms when comparing a leukotriene modifier with placebo, few studies have conclusively shown that a leukotriene modifier is any more effective in treating allergic rhinitis than an antihistamine. Results from several reported studies suggest that the addition of a leukotriene antagonist to an antihistamine is no more efficacious than antihistamine alone. However, many of these studies were small and/or primarily designed to examine the asthmatic response, with nasal symptoms being a lesser endpoint. To better understand how, where, and when leukotriene modifiers should be used in the armamentarium of therapies for allergic rhinitis, larger clinical investigations designed specifically to study allergic rhinitis need to be undertaken. We conclude that currently, the data do not support widespread use of a leukotriene modifier with or without an antihistamine in place of an intranasal corticosteroid with or without an antihistamine in the treatment of allergic rhinitis.

The role of leukotriene inhibitors in patients with paranasal sinus disease

Leukotrienes are inflammatory mediators that are known as the slow-reacting substance of anaphylaxis produced by a number of cell types including mast cells, eosinophils, basophils, macrophages, and monocytes. Synthesis of these mediators results from the cleavage of arachidonic acid in cell membranes, and they exert their biologic effects by binding and activating specific adaptors. This occurs in a series of events that lead to contraction of the human airway smooth muscle, chemotaxis, and increased vascular permeability. These effects have led to their important role in the diseases of asthma, allergic rhinitis, and possible paranasal sinusitis with the formation of nasal polyps. Because these agents lead to the production of symptoms in patients that are asthmatic, the use of leukotriene enzyme inhibitors, particularly montelukast, and zafirlukasts seem appropriate. These classes of drugs can block the binding of leukotrienes to CysLT(1) receptors. Zileuton is a 5-lipoxygenase inhibitor that prevents the formation of leukotrienes and can also result in the prevention of leukotriene activity. Demonstrated efficacy in these patients in a number of studies has also suggested their role in inhibiting nasal symptoms in asthmatic patients. In addition, it has been suggested by serendipitous observations that many of the aspirin-intolerant patients have nasal polyps and that treatment with the leukotriene inhibitors has resulted in improvement and resolution of the polyps. Therefore, these agents may also play a role in patients afflicted with chronic sinusitis with concomitant nasal polyposis. These papers are discussed in detail because this form of therapy may represent a novel way to treat patients with this malady in addition to or in lieu of surgical treatment and steroid therapy.

Update on the role of leukotrienes in the pathogenesis of atopy: a comparative review

The pathogenesis of atopic disease (AD) is controversial in humans and dogs. In humans, leukotrienes (LT) are thought to play an important role in this disease and LT inhibitors are commonly used as treatment for AD. Leukotrienes are a heterogeneous group of biologically active compounds that mediate many aspects of inflammatory and allergic reactions. This paper will review the role of LT in atopic disease in a comparative manner. Leukotriene inhibitors and their therapeutic use in the management of atopic disease in humans and dogs are discussed.

Anti-inflammatory profile of N-phenylpyrazole arylhydrazone derivatives in rats

A series of synthetic N-phenylpyrazole arylhydrazone compounds, rationally designed as mixed-hybrid isosteres of two known inhibitors of prostaglandin synthase and 5-lipoxygenase enzymes, BW-755c and CBS-1108, has been investigated for anti-inflammatory activity in the carrageenan-induced pleurisy model in rats. The compounds have different oxygenated substituent groups in the aryl group of the hydrazone framework to ensure a different range of redox properties. A new arylhydrazone derivative, 2,6-di-tert-butyl-4-(4-nitro-3-methyl-N-phenylpyrazol-5-yl-hydr azonomethyl)phenol, was also synthesized and tested for anti-inflammatory activity. Although all the compounds significantly inhibited (by 30-90%) neutrophil accumulation in the pleural cavity, there was great variability in the anti-oedematogenic effect of the compounds (3-96%). 5-(4'-Hydroxy-3'-methoxybenzylidene)hydrazone-3-methyl-4-nitrop henylpyrazole was the most active compound in this series; it had a remarkable antiinflammatory profile, almost blocking both assays. In contrast, the compound with a 2,6-di-tert-butylated hydroxybenzene ring on the hydrazone group inhibited neutrophil migration only. These results will be useful for further structure-activity relationship studies devoted to improving the dual prostaglandin synthase-5-lipoxygenase activity of these derivatives and determining the minimum structural requirements necessary for this activity.

Pharmacokinetics and pharmacodynamics of single and multiple oral doses of a novel 5-lipoxygenase inhibitor (ABT-761) in healthy volunteers

OBJECTIVE

This study evaluated the safety, pharmacokinetics and pharmacodynamics of ABT-761 [R(+)-N-[3-[5-(4-fluorophenylmethyl)-2-thienyl]-1- methyl-2-propynyl]-N-hydroxyurea], a new N-hydroxyurea analog.

METHODS

This was a randomized, double-blind, placebo-controlled, single- and multiple-dose (15-day) study of ABT-761 (50 to 200 mg/day) in healthy, nonsmoking adult male volunteers. The pharmacokinetics were evaluated by investigation of the time- and dose-dependent effects of ABT-761, and the pharmacologic selectivity of ABT-761 was evaluated based on calcium ionophore-stimulated leukotriene B4 (LTB4) and thromboxane B2 (TXB2) biosynthesis ex vivo in whole blood.

RESULTS

After single and multiple doses, mean observed time to reach maximum concentration values of ABT-761 ranged from 4.0 to 7.5 hours. Mean values for maximum concentration and area under the plasma concentration-time curve from 0 to 24 hours increased approximately linearly with dose. Mean terminal half-life and apparent volume of distribution during the terminal elimination phase of ABT-761 ranged from 15.4 to 17.8 hours and 69.5 to 78.9 L, respectively, and was dose independent. Steady state was reached on day 11 after multiple dosing. Less than 0.05% of unchanged ABT-761 was recovered in urine within the 24-hour period after day 15 dosing. Population ABT-761 plasma concentration at which 50% of the maximum possible inhibition was observed for LTB4 inhibition was 0.24 microgram/ml. No differences in mean TXB2 inhibition were observed between the subjects receiving ABT-761 and placebo.

CONCLUSIONS

These results indicate that ABT-761 is a potent and selective inhibitor of 5-lipoxygenase and the pharmacokinetics of ABT-761 are time and dose independent between 50 and 200 mg/day after single and multiple dosing.

Evaluation of the diurnal variation in the pharmacokinetics of zileuton in healthy volunteers

The diurnal variation in the pharmacokinetic parameters of zileuton were evaluated in 12 healthy male volunteers in a three-period study. Periods I and II constituted a balanced, randomized, crossover study in which a participant received a single dose of 600-mg zileuton either at 7 AM or 11 PM. In period III all participants received 600-mg doses four times daily for 5 days. The differences between the pharmacokinetics of single doses of zileuton administered at 7 AM and 11 PM were not statistically significant. Plasma concentration-time profiles of zileuton during the four daily dose intervals at steady state were also similar. Values for the pharmacokinetic parameters of zileuton after multiple doses were similar to those after single doses, with a minimal accumulation of the drug after multiple doses. Overall, there was little or no diurnal variation in the pharmacokinetic parameters of zileuton after single and multiple doses.

Eicosanoids and inflammatory bowel disease

IBD is a disease of unknown cause that involves an amplification of the inflammatory response in the intestinal mucosa. Although not the only offending agents leading to the disease, eicosanoids, the collective group of AA metabolites, may a significant role in the pathogenesis of IBD. This article reviewed the biochemical pathways of eicosanoid formation and the clinical relevance of eicosanoids to IBD. Potential strategies designed to interfere with various aspects of AA metabolism were also outlined. Further clinical trials of newer compounds may soon prove them effective in the management of IBD.

Growth control of lung cancer by interruption of 5-lipoxygenase-mediated growth factor signaling

Signal transduction pathways shared by different autocrine growth factors may provide an efficient approach to accomplish clinically significant control of lung cancer growth. In this study, we demonstrate that two autocrine growth factors activate 5-lipoxygenase action of the arachidonic acid metabolic pathway in lung cancer cell lines. Both growth factors increased the production of 5(S)-hydrooxyeicosa-6E,8Z,11Z,14Z-tetraeno ic acid (5-HETE), a major early 5-lipoxygenase metabolic product. Exogenously added 5-HETE stimulated lung cancer cell growth in vitro. Inhibition of 5-lipoxygenase metabolism by selective antagonists resulted in significant growth reduction for a number of lung cancer cell lines. Primary clinical specimens and lung cancer cell lines express the message for the 5-lipoxygenase enzymes responsible for the generation of active metabolites. In vivo evaluation demonstrated that interruption of 5-lipoxygenase signaling resulted in enhanced levels of programmed cell death. These findings demonstrate that 5-lipoxygenase activation is involved with growth factor-mediated growth stimulation for lung cancer cell lines. Pharmacological intervention with lipoxygenase inhibitors may be an important new clinical strategy to regulate growth factor-dependent stages of lung carcinogenesis.

Hydroxylamine analogs of 2,6-di-t-butylphenols: dual inhibitors of cyclooxygenase and 5-lipoxygenase or selective 5-lipoxygenase inhibitors

The preparation of hydroxylamine analogs of 2,6-di-tert-butylphenols (DTBP) and the inhibition of cyclooxygenase (CO) and 5-lipoxygenase (5-LO) by these compounds is discussed.

The pharmacokinetics of single oral doses of zileuton 200 to 800mg, its enantiomers, and its metabolites, in normal healthy volunteers

The pharmacokinetics of single oral doses of zileuton 200 to 800mg, its R(+) and S(-) enantiomers, and its N-dehydroxylated and glucuronide metabolites have been investigated in a randomised study in 16 normal male healthy volunteers. Zileuton was 93.4% bound to plasma proteins. The overall dispositional pharmacokinetics of zileuton racemate appeared to be linear. The mean dose-normalised area under the concentration-time curve from zero to infinity (AUC0-infinity) remained constant, while the mean dose-normalised peak plasma concentration (Cmax) decreased with the increase in dose, possibly because of dissolution rate-limited absorption at the higher doses. The R(+) and S(-) enantiomers of zileuton may have similar absorption profiles, although the apparent total plasma clearance of the S(-) enantiomer was 49 to 76% higher than the corresponding values for the R(+) enantiomer. The AUC0-infinity of each enantiomer increased proportionately with dose. The pharmacokinetics of the N-dehydroxylated metabolite of zileuton were highly variable, with a more than dose-proportional increase in the mean dose-normalised Cmax and area under the concentration-time curve from zero to 24 hours. The elimination of the glucuronide metabolites of the R(+) and S(-) enantiomers of zileuton was formation rate-limited. The mean percentage of the administered zileuton dose recovered in urine as glucuronide metabolites ranged from 73.1 to 76.5% and showed no dose-related differences. The renal clearance of the glucuronide metabolites of zileuton exceeded the normal glomerular filtration rate, suggesting that these metabolites may be excreted through renal tubular secretion in addition to filtration.

Pharmacodynamic and stereoselective pharmacokinetic interactions between zileuton and warfarin in humans

A double-blind parallel randomised study was conducted to assess the effects of multiple oral doses of zileuton (600mg every 6 hours) or matching placebo on the steady-state pharmacokinetics and pharmacodynamics of warfarin titrated to a prothrombin time of 14 to 18 seconds in 24 healthy adult male volunteers. Serial blood samples were collected for assessment of prothrombin times and R- and S-warfarin plasma concentrations. Coadministration of zileuton and warfarin had no effect on S-warfarin pharmacokinetics but statistically significantly increased mean R-warfarin plasma concentrations and decreased mean R-warfarin total oral plasma clearance compared with warfarin alone (by 15%). This stereoselective interaction was accompanied by an increase in mean morning (predose) and evening (12-hour postdose) prothrombin times from 17.5 to 19.8 seconds and 17.1 to 19.1 seconds, respectively; the corresponding changes in the placebo group were from 18.1 to 18.8 seconds and 17.3 to 17.5 seconds. Thus, multiple dose administration of zileuton appears to significantly alter steady-state R-warfarin pharmacokinetics and pharmacodynamics. Careful monitoring of prothrombin times with appropriate dose titration of warfarin is recommended with concurrent therapy of zileuton and warfarin.

Lack of pharmacokinetic interaction between zileuton and phenytoin in humans

A randomised double-blind crossover study was undertaken in 20 healthy adult male volunteers to assess the effects of multiple oral dose administration of zileuton (600mg every 6 hours for 8 days) on the single dose pharmacokinetics of phenytoin 300mg. Serial blood samples were collected up to 72 hours after phenytoin administration and plasma concentrations were determined by high performance liquid chromatography. Pharmacokinetic data were analysed utilising noncompartmental and Michaelis-Menten-based population pharmacokinetic analysis. Zileuton did not significantly alter the peak plasma concentration, time to peak plasma concentration, and area under the plasma concentration-time curve of phenytoin. Moreover, population analysis revealed no significant effect of zileuton on the Michaelis-Menten parameters of phenytoin. Thus, coadministration of multiple doses of zileuton (2.4 g/day) did not significantly affect the single dose pharmacokinetics of phenytoin.

Regulation of leukotriene biosynthesis

Leukotrienes are products of arachidonic acid metabolism derived through the action of the 5-lipoxygenase enzyme pathway. Leukotriene B4 has been implicated as a mediator of inflammation through induction of leukocyte and lymphocyte activation. The cysteinyl leukotrienes are important mediators of immediate hypersensitivity reactions and initiate smooth muscle contraction. Regulation of the production of leukotrienes can be achieved either through the action of direct 5-lipoxygenase inhibitors or indirect leukotriene biosynthesis inhibitors which bind to 5-lipoxygenase activating protein. Leukotriene C4 synthase and leukotriene A4 hydrolase represent alternative enzymic targets within the biosynthetic cascade. Leukotriene receptor antagonists also have important therapeutic possibilities and in particular, leukotriene D4 receptor antagonists have shown utility in the treatment of human bronchial asthma.

Inhibition of soybean lipoxygenase-1 by a diaryl-N-hydroxyurea by reduction of the ferric enzyme

It has been proposed that catechols and other antioxidants inhibit lipoxygenase activity by reducing the active Fe3+ form of the enzyme [Kemal et al. (1987) Biochemistry 26, 7064-7072]. In this model, reductively inactivated lipoxygenase can be reactivated by reaction with the hydroperoxide product in a pseudoperoxidase reaction. The contribution of enzyme reduction in the inhibition of the activity of soybean lipoxygenase-1 by the reducing inhibitor N-(4-chlorophenyl)-N-hydroxy-N'-(3-chlorophenyl)-urea (CPHU) has been evaluated quantitatively. The inhibition by CPHU of the oxygenation of linoleic acid to 13-hydroperoxy-9,11-octadecadienoic acid (13-HpODE) was accompanied by an initial lag phase which could be eliminated by the presence of exogenous 13-HpODE at the initiation of the reaction. In addition, both 13-HpODE and CPHU were found to be consumed during the lipoxygenase reaction, indicating occurrence of both oxygenase and pseudoperoxidase reactions. When analyzed individually, both the oxygenase reaction at different linoleic acid and O2 concentrations and the pseudoperoxidase reaction at different 13-HpODE and CPHU concentrations were found to follow ping-pong kinetics. A rate equation for the lipoxygenase-catalyzed reaction in the presence of reducing agent was derived considering that the inhibition of the oxygenase reaction is the combined result of 13-HpODE consumption and formation of inactive Fe2+ enzyme due to occurrence of the pseudoperoxidase reaction. By comparing the experimental data with those predicted by the rate equation, it is concluded that the inactivation of the enzyme by reduction can quantitatively account for the inhibition caused by CPHU.

Effect of a 5-lipoxygenase inhibitor, ZM 230487, on cutaneous allergic inflammation in the guinea-pig

1. Leukotrienes have potent biological effects in vitro and in vivo and are found in tissue and in biological fluids in various pathological conditions including allergic diseases. Leukotriene B4 (LTB4) is a potent stimulus for eosinophil accumulation and activation and there is much interest in determining its importance in mediating the accumulation of eosinophils at sites of allergic inflammation in vivo. In this study, we investigated the effects of a potent 5-lipoxygenase inhibitor, ZM 230487, on the accumulation of eosinophils and on local oedema formation in cutaneous inflammation in the guinea-pig. 2. The i.d. injection of increasing concentrations of arachidonic acid (AA) led to a dose-dependent accumulation of 111In-eosinophils but oedema formation was only significant at the top dose of AA tested (3 x 10(-8) mol per site). Co-injection of ZM 230487 with AA inhibited 111In-eosinophil accumulation up to 99% but the small oedema response to AA was only partially inhibited. AA-induced oedema formation was only effectively inhibited when a combination of a PAF antagonist, an antihistamine and ZM 230487 was used. 3. Local administration of the cyclo-oxygenase inhibitor, ibuprofen, partially inhibited AA-induced oedema formation suggesting that vasodilator prostaglandins may be released following i.d. injection of AA. AA-induced 111In-eosinophil accumulation was also partially inhibited by ibuprofen. 4. PAF-induced 111In-eosinophil accumulation was partially suppressed by local administration of ZM 230487. In contrast, LTB4-induced 111In-eosinophil accumulation was enhanced by ZM 230487. These data suggest that locally-released leukotrienes may modulate mediator-induced eosinophil accumulation. ZM 230487 had no effect on PAF- or LTB4-induced oedema formation. 5. ZM230487 significantly inhibited the accumulation of 111 In-eosinophils, but did not affect local oedema formation, in a passive cutaneous anaphylaxis (PCA) reaction. However, the PAF antagonist WEB 2086 either alone or in combination with ZM 230487 had no effect on "'In-eosinophil accumulation or oedema formation in the PCA reaction.6. In conclusion, it appears that a product of 5-lipoxygenase, probably LTB4, is important for the accumulation of "'In-eosinophils, but not local oedema formation, in the PCA reaction in guinea-pigskin. These data support a major role for LTB4 in allergic inflammation in the guinea-pig and make this animal (and the PCA model) suitable for studying the effects of inhibitors of leukotriene synthesis or action in vivo.

WY-50,295 tromethamine, a novel, orally active 5-lipoxygenase inhibitor: biochemical characterization and antiallergic activity

WY-50,295 tromethamine demonstrates significant 5-lipoxygenase inhibitory activity with IC50 values ranging from 0.055 microM in rat peritoneal exudate cells, to 0.16 microM in mouse macrophages, 1.2 microM in human peripheral neutrophils and 8.1 microM in rat blood leukocytes. This activity appeared selective for 5-lipoxygenase as concentrations up to 10 microM in rat peritoneal exudate cells, and 1 microM in mouse macrophages did not effect prostaglandin generation. In non-cellular enzyme assays, WY-50,295 tromethamine displayed inhibitory activity against a soluble 5-lipoxygenase from guinea pig peritoneal exudate cells (IC50 = 5.7 microM), while it was essentially inactive against 12-lipoxygenase, 15-lipoxygenase, or prostaglandin H synthetase at concentrations up to 500 microM, or against human phospholipase A2 at concentrations up to 50 microM. In purified human blood neutrophils the inhibitory activity was reversible but did not appear dependent upon substrate concentration. IN contrast, in the guinea pig cell-free 5-lipoxygenase assay changing the arachidonic acid substrate concentration from 5 to 500 microM produced a concentration-dependent reduction in inhibitory activity. WY-50,295 tromethamine inhibited the release of peptidoleukotrienes from fragmented guinea pig lung with an IC50 of 0.63 microM. When administered p.o. with a 4 h pretreatment time, WY-50,295 tromethamine inhibited ex vivo leukotriene B4 production in rat blood leukocytes with an ED50 of 19.6 mg/kg. Against an ovalbumin-induced leukotriene dependent bronchoconstriction in anesthetized sensitized guinea pigs, WY-50,295 tromethamine inhibited the ovalbumin-induced bronchoconstriction with an i.v. ED50 of 2.5 mg/kg (5 min pretreatment) and a p.o. ED50 of 7.3 mg/kg (4 h pretreatment). Significant activity was also evident with an 18 h pretreatment. Thus WY-50,295 tromethamine is an potent and selective 5-lipoxygenase inhibitor in a number of in vitro systems. Additionally the compound is orally efficacious and has a long duration of action in an allergic bronchoconstriction model. This data suggests that WY-50,295 tromethamine may have utility in the treatment of asthma and other leukotriene-dependent pathologies.