Studies on 5-lipoxygenase inhibitors. I. Synthesis and 5-lipoxygenase-inhibitory activity of novel hydroxamic acid derivatives

A series of novel hydroxamates has been prepared and tested for inhibitory activity towards rat polymorphonuclear leukocyte (PMN) 5-lipoxygenase (5-LO) in vitro and towards neutrophil migration in the rat air pouch model of inflammation in vivo. Many 3,4-dihydronaphthyl compounds were potent inhibitors of 5-LO, and several compounds were potent inhibitors of neutrophil migration. The most potent 3,4-dihydronaphthyl compound, N-[[(3,4-dihydro-5-phenoxy)-2-naphthyl]methyl]-N-hydroxy-N'-ethylurea (FR122788, 18) had an IC50 of 25 nM in the 5-LO assay, and strongly reduced neutrophil migration in the rat air pouch model at 1 mg/kg (p.o.). FR122788 also had an ameliorating effect in a rat hepatitis model induced by D-galactosamine, with an ED50 values of 14.6 mg/kg (p.o.) for glutamate oxaloacetate transaminase (GOT) and 16.8 mg/kg (p.o.) for glutamate pyruvate transaminase (GPT).

Effect of the 5-lipoxygenase inhibitor, fenleuton, on antigen-induced neutrophil accumulation and lung function changes in horses with chronic obstructive pulmonary disease

The leukotrienes (LT) LTD4 and LTB4 have been shown to cause bronchoconstriction and neutrophil accumulation, respectively, in horse lungs. Such changes are characteristic of the equine allergic respiratory disease, chronic obstructive pulmonary disease (COPD). To further investigate the role of these putative mediators in the pathogenesis of equine COPD the effect of a 5-lipoxygenase inhibitor, fenleuton, on antigen-induced changes in horses with this condition has been examined. Six horses with COPD underwent a series of four antigen challenges, one month apart, with placebo pre-treatment on three occasions and fenleuton (4 days oral dosing 5 mg/kg) pre-treatment on one occasion. Three horses received fenleuton prior to the second challenge and three horses received the drug prior to the fourth antigen challenge. Changes in radiolabelled neutrophil distribution, lung function and peripheral leucocyte counts were monitored on each occasion for 7 h following the start of antigen challenge. Antigen challenge caused an increase in radioactive counts over the lungs and a decrease in peripheral leucocyte count. Neither response was affected by fenleuton pre-treatment. Mean maximal changes in pleural pressure (delta Pplmax) and respiratory rate were also unaffected by fenleuton pre-treatment. However, in the two horses which responded to antigen-challenge with a particularly marked increase in delta Pplmax (> 15 cm H2O), prior administration of fenleuton reduced the response by 64 and 63%. These results suggest that 5-lipoxygenase inhibitors warrant further investigation as bronchodilators in equine COPD.

A practical guide to the management of distal ulcerative colitis

This article reviews the role of corticosteroids, sulfasalazine and mesalazine (5-aminosalicylic acid, mesalamine), immunosuppressive agents and alternative novel drugs for the treatment of distal ulcerative colitis. Short cycles of traditional, rectally administered corticosteroids (methylprednisolone, betamethasone, hydrocortisone) are effective for the treatment of mild to moderately active distal ulcerative colitis. In this context, their systemic administration is limited to patients who are refractory to either oral 5-amino-salicylates, topical mesalazine or topical corticosteroids. Of no value in maintaining remission, the long term use of either or topical corticosteroids may be hazardous. A new class of topically acting corticosteroids [budesonide, fluticasone, beclomethasone dipropionate, prednisolone-21-methasulphobenzoate, tixocortol (tixocortol pivalate)] represents a valid alternative for the treatment of active ulcerative colitis, and may be useful in the treatment of refractory distal ulcerative colitis. Although there is controversy concerning dosage or duration of therapy, oral and topical mesalazine is effective in the treatment of mild to moderately active distal ulcerative colitis. Sulfasalazine and mesalazine remain the first-choice drugs for the maintenance therapy of distal ulcerative colitis. Evidence exists showing a trend to a higher remission rate with higher doses of oral mesalazine. Topical mesalazine (suppositories or enemas) also is effective in maintenance treatment. For patients with chronically active or corticosteroid-dependent disease, azathioprine and mercaptopurine are effective in reducing either the need for corticosteroids or clinical relapses. Moreover, they are effective for long term maintenance remission. Cyclosporin may be useful in inducing remission in patients with acutely severe disease who do not achieve remission with an intensive intravenous regimen. Existing data suggest that azathioprine and mercaptopurine may be effective in prolonging remission in these patients. The role of alternative drugs for the treatment of distal ulcerative colitis and its different forms is reviewed. In particular data are reported concerning the effectiveness of 5-lipoxygenase inhibitors, topical use of short chain fatty acids, nicotine, local anaesthetics, bismuth subsalicylate enema, sucralfate, clonidine, free radical scavengers, heparin and hydroxychloroquine.

Benefits from adding the 5-lipoxygenase inhibitor zileuton to conventional therapy in aspirin-intolerant asthmatics

From bronchoprovocation studies and investigations of the acute effects of drugs that inhibit leukotrienes (LT), the hypothesis has emerged that leukotrienes are important mediators of airway obstruction and other symptoms in aspirin-intolerant asthma (AIA). However, it has yet not been shown if subjects with AIA respond favorably to clinical treatment with leukotriene inhibitors. Therefore, in a double-blind placebo-controlled crossover study, we examined the effects of 6 wk of treatment with the leukotriene-pathway inhibitor zileuton (600 mg, four times daily) in 40 patients with well-characterized AIA. The treatment was added to existing therapy, which included medium to high doses of inhaled (average daily dose 1,030 microg of beclomethasone or budesonide) or oral glucocorticosteroids (4 to 25 mg/d) for all but one of the patients. On top of this treated baseline, there were no significant effects of adding placebo, indicating that their asthma was kept relatively stable. However, there was an acute and chronic improvement in pulmonary function after treatment with zileuton, expressed both as increased FEV1 from baseline compared with placebo, and higher morning and evening peak expiratory flow rate (PEFR) values on zileuton treatment compared with placebo. The improvements occurred despite lower use of rescue bronchodilator with zileuton. Zileuton also diminished nasal dysfunction, which is one of the cardinal signs of AIA. There was a remarkable return of smell, less rhinorrhea, and a trend for less stuffiness and higher nasal inspiratory flow during treatment with zileuton. Zileuton caused a small but distinct reduction of bronchial hyperresponsiveness to histamine and inhibited aspirin-induced bronchoconstriction. Zileuton inhibited urinary excretion of LTE4 but did not change airway reactivity to inhaled LTD4, supporting that zileuton specifically inhibited leukotriene biosynthesis. The findings indicate that leukotrienes are important mediators of persistent airway obstruction and chronic nasal dysfunction in AIA. The study also suggests that addition of a leukotriene pathway inhibitor such as zileuton may bring about greater control of asthma than what is achieved by treatment with medium to high doses of glucocorticosteroids alone.

Pharmacokinetics and pharmacodynamics of fenleuton, a 5-lipoxygenase inhibitor, in ponies

Leukotrienes, products of the 5-lipoxygenase pathway of arachidonic acid metabolism, possess properties consistent with their involvement in a range of inflammatory diseases. In this study the pharmacokinetics and pharmacodynamics of the selective 5-lipoxygenase inhibitor, fenleuton, have been examined in the horse. Orally administered fenleuton (four 5 mg kg(-1) doses, given once daily) was absorbed from the gastrointestinal tract, and penetrated readily into tissue cage exudate, the ratio of the plasma:exudate AUC0-48h being 0.90+/-0.02 (n=6). Ionophore-stimulated leukotriene (LT) B4 synthesis, measured ex vivo in whole blood as immunoreactive LTB4, was significantly (P<0.05) inhibited throughout the 48 hour sampling period. Low levels of immunoreactive LTB4 were detected in transudate and these did not increase following addition of carrageenan to the tissue cages. Fenleuton had no significant inhibitory effect on exudate LTB4 concentrations. A reduction in carrageenan-induced skin swelling occurred, although this did not achieve statistical significance. The results obtained in this study suggest that fenleuton could be used to examine the role of LTs in inflammatory diseases of the horse.

Inhibition of cancer cell proliferation by disruption of interdigitated/concatenated hierarchies of metabolic control/implementation processes: a proposal

With a combination of inhibitors at less than their individual 'therapeutic' concentrations directed against dissimilar cellular hierarchical developmental controls and 'downstream' metabolic pathways, it may be possible to modulate the biologic behavior of malignantly transformed cells synergistically. Ideally the cumulative systemic toxicity of such a 'polytherapy' would be reduced.

Effects of single-dose zileuton on bronchial hyperresponsiveness in asthmatic patients treated with inhaled corticosteroids

The aim of the study was to determine whether zileuton, an inhibitor of 5-lipoxygenase, attenuated bronchial hyperresponsiveness (BHR) in asthmatic subjects who had marked BHR during maintenance treatment with inhaled corticosteroids (ICS). In a randomized, double-blind, placebo-controlled, cross-over study, a challenge test with histamine (provocative concentration of histamine producing a 20% fall in forced expiratory volume in one second (FEV1) (PC20,Hist)) and with ultrasonically nebulized distilled water (UNDW) (provocative dose of UNDW producing a 20% fall in FEV1 (PD20,UNDW)) was performed in seven patients with asthma after intake of either 400 mg zileuton or placebo. All patients (mean age 33 yrs, mean FEV1 111% of predicted) had marked BHR, as indicated by a mean PD20,UNDW of 4.74 mL under treatment for at least 6 months with up to 800 microg ICS (mean 536 microg daily). On four different occasions, separated by at least 5 days, two UNDW and two histamine challenge tests were performed in random order 3 h after a morning dose of either zileuton or placebo. Neither zileuton nor placebo changed baseline airway calibre prior to provocation. Zileuton increased PC20,Hist from 0.99 to 5.64 mg x mL(-1) (2.1 doubling doses; p<0.03 compared to placebo), and increased PD20,UNDW from 3.10 to 9.31 mL (1.3 doubling doses; p<0.05 compared to placebo). In conclusion, a single dose of 400 mg zileuton attenuates bronchial hyperresponsiveness to histamine and ultrasonically nebulized distilled water in asthmatic patients with marked bronchial hyperresponsiveness during treatment with inhaled corticosteroids.

Dietary fish oil or lofrin, a 5-lipoxygenase inhibitor, decrease the growth-suppressing effects of coccidiosis in broiler chicks

Broiler chicks were fed a diet containing 4% of either corn oil or fish oil from 3 to 14 d of age. From Days 15 to 23, half of the chicks in each dietary treatment were fed Lofrin (an experimental 5-lipoxygenase inhibitor) at 33 micrograms/kg feed. The remaining chicks within each dietary treatment were the untreated controls. At 24 d of age, half of the chicks within each diet-Lofrin treatment group were each infected with 4.6 x 10(4) sporulated Eimeria tenella oocysts, resulting in a 2 x 2 x 2 factorial arrangement of treatments. Body weight gain, feed consumption, and feed conversion efficiency were determined throughout the study. At 27 d of age, blood, liver, and ceca were sampled. Plasma tumor necrosis factor and hemopexin, hepatic fatty acid composition, and cecal inflammatory cell infiltration were determined. Liver fatty acid composition tended to reflect that of the diet. Chicks fed fish oil had livers that were enriched in (n-3) polyunsaturated fatty acids (PUFA) at the expense of (n-6) PUFA. Chicks fed fish oil gained body weight more rapidly than those fed corn oil. Infection of chicks with Eimeria decreased body weight gain of chicks fed corn oil, but not of chicks fed fish oil. The addition of Lofrin to the corn oil diets abrogated the growth-suppressing effects of infection, although there was no Lofrin effect among chicks fed fish oil. There was a diet by Lofrin interaction in which Lofrin treatment of birds fed corn oil decreased feed consumption and increased feed conversion efficiency, but had no effect on chicks fed diets containing fish oil. Plasma hemopexin was greater, but tumor necrosis factor was lower, in chicks fed fish oil than in chicks fed corn oil. Eimeria infection significantly increased cecal inflammatory cell infiltration across all dietary treatments. There were no clear relationships between growth rate or efficiency and the severity of the inflammatory response to Eimeria infection, as indicated by hemopexin levels and cecal inflammatory scores. These results indicate that Lofrin or fish oil, both of which modify eicosanoid metabolism, attenuate the growth-depressing effects of an Eimeria tenella infection.

Neither platelet activating factor nor leukotrienes are critical mediators of liver injury after lipopolysaccharide administration

The intravenous administration of lipopolysaccharide (LPS) to rats results in liver lesions characterized by the infiltration of both platelets and neutrophils into the liver and by midzonal hepatocellular necrosis. The liver injury is dependent on neutrophils, platelets and the coagulation system, as removal or inhibition of any of these components inhibits the development of hepatocellular necrosis. Platelet activating factor (PAF) and the cysteinyl leukotrienes (LTs) are potent inflammatory lipids that are critical for the development of some LPS-mediated alterations. To test the hypothesis that PAF, alone or in combination with LTs, contributes to the development of liver injury during LPS exposure, we conducted studies with the PAF receptor antagonist, WEB 2086, and the 5-lipoxygenase inhibitor, Zileuton. Female, Sprague-Dawley rats were pretreated with WEB 2086 (10 mg/kg, i.p.) alone or with Zileuton (40 mg/kg, p.o.) 1 h before the administration of LPS (4 mg/kg, i.v.) or its saline vehicle. Treatment with WEB 2086, alone or in combination with Zileuton, did not inhibit LPS-mediated hepatic neutrophil infiltration or liver injury, as assessed by histologic evaluation and increases in plasma alanine aminotransferase activity. Pretreatment with these agents also had no effect on the activation of the coagulation system or on the thrombocytopenia induced by LPS. These results suggest that PAF, alone or in combination with 5-lipoxygenase products, is not a critical mediator of LPS-induced hepatocellular injury in this model.

Pharmacology of the 5-lipoxygenase inhibitors BAY Y 1015 and BAY X 1005 in the horse

Calcium ionophore A23187 induced time and concentration dependent production of immunoreactive leukotriene (LT) B4 by equine heparinized whole blood in vitro. Time dependent production of immunoreactive LTB4 by equine neutrophils and immunoreactive LTC4 by equine eosinophils in vitro was also demonstrated. The 5-lipoxygenase activating protein (FLAP) inhibitors, BAY X 1005 and BAY Y 1015, produced concentration dependent inhibition of ionophore-induced LTB4 synthesis by equine whole blood (mean +/- SEM IC50s n = 5; 6.14 +/- 0.28 microM vs. 12.30 +/- 0.75 microM for BAY Y 1015 and BAY X 1005, respectively) and neutrophils (mean +/- SEM IC50s n = 5; 0.003 +/- 0.001 microM vs. 0.045 +/- 0.021 microM for BAY Y 1015 and BAY X 1005, respectively) and LTC4 synthesis by equine eosinophils (mean +/- SEM IC50s n = 5; 0.0036 +/- 0.0002 microM and 0.108 +/- 0.023 microM for BAY Y 1015 and BAY X 1005, respectively) in vitro. In all three assays, BAY Y 1015 was more potent than BAY X 1005, and for both compounds much higher concentrations were required to inhibit LT synthesis by whole blood compared to isolated neutrophils and eosinophils. Plasma concentration-time relationships and pharmacokinetic parameters for BAY Y 1015 administered intravenously and orally to six horses at a dosage of 10 mg/kg in a two period cross-over study were established. The study also evaluated the anti-inflammatory properties of BAY Y 1015 and its ability to inhibit ex vivo whole blood LTB4 synthesis and in vivo LTB4 synthesis in a tissue cage model of acute inflammation. At this dosage, BAY Y 1015 failed to significantly inhibit immunoreactive LTB4 synthesis or the oedema produced by intradermal injection of the mild irritant, carrageenan.

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.

Pharmacokinetics of zileuton and its metabolites in patients with renal impairment

The pharmacokinetics of zileuton and its conjugated metabolites were evaluated in patients with chronic renal impairment. Five healthy volunteers (creatinine clearance > 90 mL/min), five patients with renal failure requiring hemodialysis, six with mild (creatinine clearance, 60-90 mL/min), eight with moderate (creatinine clearance, 30-59 mL/min), and six with severe (creatinine clearance < 30 mL/min) renal impairment participated in the study. Zileuton was well tolerated by all participants including those with severe renal impairment and those receiving hemodialysis. The pharmacokinetics of zileuton were similar in healthy volunteers; in patients with mild, moderate and severe renal impairment; and in patients with renal failure requiring hemodialysis. The mean metabolite/parent-area ratios for the pharmacologically inactive zileuton glucuronides progressively increased with the decline in renal function. A very small percentage of the administered zileuton dose (< 0.5%) was removed by hemodialysis. Therefore, adjustment in the dose regimen of zileuton does not appear to be necessary for patients with various degrees of renal impairment and patients with renal failure requiring hemodialysis.

5-Lipoxygenase and endotoxin-induced microvascular albumin exchanges and leucocyte recruitment in guinea-pig lungs

The interference of the 5-lipoxygenase inhibitor, BW B70C ((E)-N-(3-[3-(4-fluorophenoxy)phenyl]-1(R,S)-methyl prop-2-enyl)-N-hydroxyurea), with Escherichia coli lipopolysaccharide (endotoxin)-induced lung leucocyte sequestration and microvascular albumin exchanges was evaluated in the anaesthetised guinea-pig using radioactive tracers, in parallel to the effects on cell counts in the broncho-alveolar lavage fluid, blood tumour necrosis factor (TNF-alpha) content, secretion of phospholipase A2 and synthesis of leukotriene C4 by alveolar macrophages. Intravenous injections of 0.1 or 1 mg/kg endotoxin induced lung leucocyte sequestration but only the higher dose induced an increase in albumin microvascular exchanges and the infiltration of leucocytes towards the airway lumen. Leukotriene B4, a potential mediator of the 5-lipoxygenase-dependent endotoxin effects, induced a rapid and transient lung leucocyte sequestration and leucopenia associated with a more progressive increase in microvascular exchanges. The 5-lipoxygenase inhibitor, BW B70C, injected i.p. (30 mg/kg) prevented leukotriene C4 synthesis by alveolar macrophages and reduced leucocyte migration to the airways lumen as well as albumin microvascular leakage but did not affect the endotoxin-induced increase in the blood level of TNF-alpha and of secreted phospholipase A2. However, BW B70C failed to modify vascular leucocyte margination induced by 1 mg/kg endotoxin, suggesting that, apart from a role of 5-lipoxygenase, alternative pathways operate in response to endotoxin in guinea-pig.

New ulcerative colitis model induced by sulfhydryl blockers in rats and the effects of antiinflammatory drugs on the colitis

We tried to produce a new ulcerative colitis model in rats by topical administration of sulfhydryl blockers. After male SD rats were fasted for 24 hr, 100 microliters of 3% N-ethylmaleimide (NEM) or iodoacetamide (IA) was introduced into the colon via a Nelaton's catheter. Both NEM and IA caused severe diarrhea with rectal bleeding and decreased body weight for about 7 days. At autopsy, adhesions and dilatation of the colon and severe mucosal lesions were observed. Both the weight and myeloperoxidase activity of the colon increased markedly. Maximum changes were observed within 1-3 days followed by gradual recovery, but even on day 21, some abnormalities were still observed. The ulceration and inflammation of the colon were confirmed by histological studies. Antiinflammatory drugs such as indomethacin inhibited the inflammation of the colon by NEM, but aggravated the ulceration. These results revealed that sulfhydryl blockers instilled into the colon caused ulcerative colitis in the rat. This model may be useful in studies on the pathogenesis of ulcerative colitis and the evaluation of drugs for therapy. Furthermore, it was suggested that antiinflammatory drugs may delay the healing of colonic ulcers.

Randomized trial of zileuton in patients with moderate asthma: effect of reduced dosing frequency and amounts on pulmonary function and asthma symptoms. Zileuton Study Group

This 6-month, randomized, multicenter study was designed to determine whether patients who had been treated with the leukotriene pathway inhibitor zileuton 600 mg four times daily (QID) for 2 months could be maintained at the same level of pulmonary function, symptom control, and beta-agonist use with less frequent dosing--first 600 or 800 mg three times daily (TID) and then twice daily (BID). A total of 278 patients with chronic asthma, ages 16 to 70, participated at 25 US centers. All had a 1-second forced expiratory volume (FEV1) of 35%-75%, reversible airway disease, and a nonsmoking history of 1 year. An 8-week open-label period (zileuton 600 mg QID) was followed by a 16-week double-blind period, in which patients who responded to the QID treatment were randomized to receive zileuton 600 or 800 mg TID for 8 weeks and then rerandomized to receive zileuton 600 or 800 mg BID for another 8 weeks. Primary outcomes were FEV1 and asthma symptom scores; secondary outcomes were peak expiratory flow rate, beta-agonist use, and asthma exacerbations requiring steroid rescue. Patients who showed improvements in lung function when treated with zileuton 600 mg QID demonstrated minimal decreases in FEV1 and comparable peak expiratory flow rates, symptom control, beta-agonist use, and systemic corticosteroid rescue when being treated with lower doses and/or less frequent doses of zileuton. Patients who demonstrate improved asthma control with zileuton 600 mg QID may be able to reduce their daily dosage and/or frequency while still maintaining the same level of symptom control.

Acute and chronic effects of a 5-lipoxygenase inhibitor in asthma: a 6-month randomized multicenter trial. Zileuton Study Group

BACKGROUND

Leukotrienes produced by the 5-lipoxygenase pathway of arachidonic acid metabolism may mediate bronchoconstriction and inflammatory changes important in the pathophysiology of asthma. Leukotriene inhibition may be effective in asthma management.

OBJECTIVE

This clinical trial was performed to assess the long-term efficacy and safety of zileuton, an inhibitor of 5-lipoxygenase.

METHODS

In this multicenter, double-blind, parallel-group, placebo-controlled trial, 600 mg of zileuton, 400 mg of zileuton, or placebo was given orally, each four times daily for 6 months. Patients with mild to moderate asthma (n = 373), 18 to 62 years of age, being managed with regularly inhaled beta-agonist alone, were randomized to the zileuton or placebo groups (n = 122 to 126). Outcome measures included serial spirometry, daily peak expiratory flow rates, daytime and nocturnal symptoms, frequency of beta-agonist use, and number of asthma exacerbations treated with systemic corticosteroids.

RESULTS

An acute bronchodilatory effect was observed 2 to 5 hours after the initial dose of medication in both 400 mg zileuton and 600 mg zileuton groups compared to the placebo group. Both zileuton groups had significantly greater improvements in FEV1 than did the placebo group by day 8. On day 36, FEV1 improved 16% and 12% from baseline for patients treated with 600 mg zileuton and 400 mg zileuton, respectively, compared with an improvement of 6% for the placebo-treated group (p < 0.01, zileuton 600 mg vs placebo). Blood eosinophil levels were significantly reduced in both zileuton-treated groups compared with the placebo group. In the group receiving 600 mg zileuton, morning peak expiratory flow rate improved by 7% to 10%; daytime and nocturnal symptoms decreased by 37% and 31%, respectively; beta-agonist use decreased by 31%; and the proportion of patients requiring steroid rescue medication during the study was reduced by 62% (p < 0.05 for all comparisons of zileuton, 600 mg, vs placebo). Improvements were sustained over 6 months. Adverse events were similar in the three groups with no apparent, dose-related side effects.

CONCLUSION

Zileuton produces objective and subjective improvements in patients with mild to moderate asthma and is well tolerated.

Evaluation of anti-inflammatory potential of fixed oil of Ocimum sanctum (Holybasil) and its possible mechanism of action

The fixed oil of Ocimum sanctum (Labiatae) was found to possess significant anti-inflammatory activity against carrageenan- and different other mediator-induced paw edema in rats. Significant inhibitory effect was also observed in castor oil-induced diarrhoea in rats. It also inhibited arachidonic acid and leukotriene-induced paw edema. The results of anti-inflammatory activity of Ocimum sanctum support the dual inhibition of arachidonate metabolism as indicated by its activity in inflammation models that are insensitive to selective cyclooxygenase inhibitors. On the basis of the findings it may be inferred that Ocimum sanctum may be a useful anti-inflammatory agent which blocks both the pathways, i.e. cyclooxygenase and lipoxygenase, or arachidonic acid metabolism.

Inhibitory effect of TMK688 on skin tumor initiation caused by 7,12-dimethylbenz[a]anthracene in relation to inhibition of aryl hydrocarbon hydroxylase activity and Cyp1a1 mRNA induction

Oral administration of TMK688 (1-([5'-(3"-methoxy-4"-ethoxycarbonyloxyphenyl)-2',4'-pentadien oyl] aminoethyl)-4-diphenylmethoxypiperidine: 30 mg/kg) at 6 h and 30 min prior to and at 30 min after a single topical application of 7,12-dimethylbenz[a]anthracene (DMBA) to dorsal skins of mice reduced both tumor incidence and number of tumors per mouse in the DMBA-initiated and 12-O-tetradecanoylphorbol-13-acetate (TPA)-promoted two-stage mouse skin carcinogenesis. TMK688 and its active metabolite TMK777 (1-([5'-(3"-methoxy-4"- hydroxyphenyl)-2',4'-pentadienoyl]-aminoethyl)-4-diphenylmethox y piperidine) inhibited 3-methylchol-anthrene (MC)-induced epidermal aryl hydrocarbon hydroxylase (AHH) activity in a concentration-dependent manner. IC50 of TMK688 and TMK777 was 0.18 and 0.01 mumol/l, respectively. Oral administration of TMK688 (30 mg/kg) almost completely suppressed Cyp1a1 mRNA levels in mouse epidermis induced by a topical application of MC (40 mg/kg) or benzo[a]pyrene (200 nmol) to mouse skin. Oral administration of TMK688 (30 mg/kg) also almost completely inhibited induction of epidermal AHH activity caused by a topical application of MC. These results indicate that oral administration of TMK688 inhibited DMBA-caused skin tumor initiation at least in part by inhibiting Cyp1a1 mRNA induction and epidermal AHH activity.

No pharmacokinetic or pharmacodynamic interaction between theophylline and the leukotriene biosynthesis inhibitor BAY x 1005

An open, randomized, three-period crossover study was conducted to compare the steady-state pharmacokinetics, pharmacodynamics, and tolerability of concomitant administration of BAY x 1005 and theophylline in 12 healthy volunteers. BAY x 1005 (250 mg twice daily; treatment A) and theophylline (400 mg twice daily; treatment B), were administered alone and concomitantly (treatment C) for 6 days with a final morning dose on day 7. The treatments were separated by washout periods of at least 5 days. Pharmacokinetic parameters were derived from concentrations of BAY x 1005 and theophylline as measured by high-performance liquid chromatography in plasma collected before the morning dose on days 5 and 6 and at various times on day 7 of each period until 24 hours after drug administration. Adverse events, vital signs, electrocardiograms, and clinical laboratory studies were monitored as safety parameters. Levels of leukotriene B4 (LTB4) were assessed in plasma collected on days 1 and 7. The treatments were well tolerated by all participants. The ratios of maximum concentration (Cmax) and area under the concentration-time curve for one 12-hour dosing interval (AUC tau) for treatment C versus B for theophylline on day 7 was 98% for both parameters. For BAY x 1005, the ratios of treatment C versus treatment A were 94% for Cmax and 101% for AUC tau. Plasma LTB4 remained virtually unchanged during either treatment. Steady-state concentrations of theophylline were not affected by concomitant BAY x 1005 intake, and addition of theophylline had no clinically relevant effect on steady-state plasma concentrations of BAY x 1005. The combination of theophylline and BAY x 1005 did not lead to a change in nature, intensity, or frequency of adverse events.

Intracolonic administration of zileuton, a selective 5-lipoxygenase inhibitor, accelerates healing in a rat model of chronic colitis

BACKGROUND

5-Lipoxygenase products play a part in inflammatory response.

AIMS

The effect of intracolonic administration of zileuton (a 5-lipoxygenase inhibitor) on colonic damage and eicosanoid local release was assessed in a rat model of colitis.

METHODS

Ninety rats with trinitrobenzenesulphonic acid induced colitis were randomised to receive placebo, 5-aminosalicylic acid (50 mg/kg), or zileuton (50 mg/kg) intracolonically for four weeks. Local eicosanoid release was monitored by intracolonic dialysis throughout the study. The colon was removed for macroscopic and histological assessment at weeks 1, 2, and 4 after colitis induction in 10 rats of each group.

RESULTS

Zileuton significantly reduced macroscopic damage score after four weeks of treatment in comparison with the other two groups (p = 0.034). In addition, zileuton administration significantly increased the intracolonic release of both thromboxane B2 at week 1 (p = 0.05) and prostaglandin E2 at weeks 2 and 4 (p < 0.05). Zileuton and 5-aminosalicylic acid decreased leukotriene B4 release by 90% at day 3.

CONCLUSIONS

Intracolonic zileuton, compared with 5-aminosalicylic acid and placebo, seems to improve the course of the disease in a model of chronic colitis. This effect may be related to an increased and maintained production of prostaglandin E2 together with inhibition of leukotriene B4 synthesis.

Involvement of leukotrienes in allergic pleurisy in actively sensitized rats: inhibition by the lipoxygenase inhibitor T-0757 of the increase in vascular permeability and leukotriene E4 production

The relative contributions of inflammatory mediators to the increase in vascular permeability in antigen-induced pleurisy were examined in rats actively sensitized with ovalbumin. The effects of various inhibitors were assessed on the exudate volume and plasma exudation rate in the pleural cavity. Two peaks were observed in plasma exudation rate at 0.5 and 3 h after antigen challenge. At 0.5 h, there was a marked decrease in the histamine content of the pleural cells and also a sharp increase in the LTE4 level in the exudate, which was inhibited dose-dependently by the lipoxygenase inhibitor T-0757. Indomethacin and cyproheptadine both depressed exudate volume and exudation rate, whereas T-0757 only reduced the exudation rate. At 3 h, a substantial LTE4 concentration was still detected in the exudate, and the exudation rate was depressed by T-0757 and indomethacin, but not by cyproheptadine. These results suggest that histamine is involved mainly in the early phase, and leukotrienes predominantly contribute to the later phase of exudation. Prostaglandins appear to be involved in both phases. Allergic pleurisy of rats, therefore, may be a suitable model to examine the roles of these inflammatory mediators.

Effect of treatment with zileuton, a 5-lipoxygenase inhibitor, in patients with asthma. A randomized controlled trial. Zileuton Clinical Trial Group

OBJECTIVE

To study the effect of 3 months of treatment with zileuton, an inhibitor of the enzymatic pathway (5-lipoxygenase) leading to leukotriene formation, on disease control in patients with mild to moderate asthma.

DESIGN

Randomized, double-blind, parallel-group study in 401 patients. A 10-day placebo lead-in was followed by a double-blind treatment period of 13 weeks.

SETTING

Asthma study clinics in university hospitals and private practices.

PATIENTS OR OTHER PARTICIPANTS

Patients with mild to moderate asthma (forced expiratory volume in the first second [FEV1], 40% to 80% of predicted) whose only treatment was inhaled beta-agonists.

INTERVENTIONS

Treatment with 600 mg or 400 mg of zileuton or placebo (each taken four times daily.)

MAIN OUTCOME MEASURES

Frequency of asthma exacerbation requiring treatment with corticosteroids, use of inhaled beta-agonists, pulmonary function tests, asthma symptom assessment, and quality-of-life evaluation. Safety was evaluated by monitoring adverse events.

RESULTS

Only eight (6.1%) of 132 patients receiving 600 mg of zileuton four times a day required corticosteroid treatment for asthma vs 21 (15.6%) of 135 patients receiving placebo (P=.02), giving a relative risk of 2.6. At the time of expected peak drug concentration, the average FEV1 improved 15.7% in the 600-mg zileuton group vs 7.7% in the placebo group (P=.006). Quality-of-life assessments significantly improved in the 600-mg zileuton group and not in the placebo group (P=.007 for the overall score). Elevations in liver function tests (more than three times normal), all of which reversed with drug withdrawal, occurred in five patients (P=.03 vs placebo), three patients (P=.12 vs placebo), and no patients treated with 600 mg of zileuton, 400 mg of zileuton, or placebo, respectively.

CONCLUSIONS

Three months of 5-lipoxygenase inhibition produced a significant improvement in asthma control. These data indicate that 5-lipoxygenase products of arachidonic acid metabolism are mediators of inflammation with an important role in the biology of asthma.

Effect of sodium nitroprusside and diethylcarbamazine on hypoxic pulmonary vasoconstriction and regional distribution of pulmonary blood flow in experimental pneumonia

The interaction between the effects of indomethacin and sodium nitroprusside or diethylcarbamazine infusion on the efficacy of hypoxic pulmonary vasoconstriction (HPV) and regional distribution of lung blood flow was studied in 15 pentobarbital-anesthetized dogs with acute pneumonia caused by Pseudomonas aeruginosa. After induction of pneumonia central hemodynamics, gas exchange, and regional distribution of lung blood flow (radionuclide-labeled microsphere method) were measured during ventilation of both lungs with oxygen and again with one lung ventilated with nitrogen. The dogs were then randomly assigned to one of three treatment groups: Group I (n = 5) received indomethacin alone (2 mg/kg); Group I-D received indomethacin and diethylcarbamazine (50 mg/kg over 20 min followed by 1 mg/kg/min for the rest of the experiment); Group I-N (n = 5) received indomethacin with sodium nitroprusside to achieve a 20- to 30-mm Hg reduction in mean blood pressure. All measurements were then repeated during both oxygen ventilation and one-lung nitrogen ventilation. In all three groups there was no effect of nitrogen inhalation on distribution of lung blood flow prior to drug treatment, indicating absence of HPV. After treatment, in Group I, perfusion of the pneumonic lung fell from 0.27 +/- 0.08 to 0.10 +/- 0.03 (p < 0.05) of total lung blood flow, and nitrogen ventilation of the left lung reduced perfusion to that region from 0.23 +/- 0.02 to 0.13 +/- 0.02 (p < 0.05), indicating restoration of HPV. In Groups I-D and I-N, HPV was persistently absent or markedly attenuated after treatment, but the percentage of the cardiac output perfusing the pneumonia region fell by an amount similar to that in Group I (0.26 +/- 0.07 to 0.11 +/- 0.04 in Group I-D and 0.35 +/- 0.03 to 0.21 +/- 0.06 in Group I-N, both p < 0.05). Because these two chemically unrelated pulmonary vasodilators effectively blocked HPV restoration but had no effect on vasoconstriction in the pneumonia region after indomethacin, it is concluded that regional lung blood flow redistribution in pneumonia is mediated by a mechanism other than HPV.

Reducing ischemia-reperfusion injury in rat island groin flaps by dexamethasone and BW755C

Despite the known effectiveness of anti-inflammatory therapy in reducing reperfusion injury, no studies to date involve the use of anti-inflammatory therapy in reducing ischemia-reperfusion injury in fasciocutaneous flaps. Dexamethasone (a phospholipase A2 inhibitor) and specific cyclooxygenase and lipoxygenase inhibitors (indomethacin and BW755C) were administered to rats with ischemic island groin (fasciocutaneous) flaps. Significant improvement in ischemic flap survival was found with dexamethasone and BW755C. The mode of action of dexamethasone was not specifically investigated in our study; however, it may suppress neutrophil function and reduce ischemia-reperfusion injury in its shared ability with BW755C to reduce the formation of leukotrienes. Dexamethasone could be applied in the clinical setting to reduce ischemic flap loss by attenuating the systemic inflammatory response to reperfused ischemic-damaged tissue.

Selective blockade of leukotriene production by a single dose of the FPL 64170XX 0.5% enema in active ulcerative colitis

5-Lipoxygenase products of arachidonic acid metabolism are thought to play a central role in the secondary amplification of the inflammatory response of several inflammatory diseases, including ulcerative colitis. FPL 64170XX is a selective inhibitor of the enzyme 5-lipoxygenase. Concentrations of leukotriene B4 and prostaglanding E2 in rectal dialysis fluid from 23 males with clinically and sigmoidoscopically active, distally located ulcerative colitis were measured by radioimmunoassays in a double-blind, placebo-controlled, parallel design study before and after rectal administration of an enema containing 0.5% of FPL 64170XX. Repeated measures analysis of leukotriene B4, after adjusting for baseline, showed a significant treatment effect (P = 0.0014). The concentration of leukotriene B4 from rectal dialysates in patients receiving the active drug dropped to 15% (95% confidence interval 5-40%) of the placebo level in the second dialysis following administration of FPL 64170XX 0.5%. By contrast, prostaglanding E2 concentrations doubled (P = 0.0068) in patients receiving FPL 64170XX 0.5% with no change in the placebo group. These findings demonstrate that a single dose of FPL 64170XX 0.5% enema selectively blocks the generation of the 5-lipoxygenase product, leukotriene B4, to a mean of 85% in the target tissue of inflammation. Topical administration of this new leukotriene synthesis inhibitor may prove to be a clinically useful approach to the treatment of active, distally located ulcerative colitis.