Search PubMed⌕ Search

Biomedical subjects

R L Bell

Publications and source records attributed to R L Bell.

At least 37 records · Page 2Linked to original sources
PubMed1998

The role of tissue mast cells in polyacrylamide gel-induced inflammation in mice.

OBJECTIVE AND DESIGN: In the present study, we investigated the role of mast cells in a model of polyacrylamide gel (PAG)-induced inflammation in mice. SUBJECTS: Balb/c mice and two strains of mast cell deficient mice (WBB6F1/J-W/Wv, WCB6F1/J-S1/S1d). TREATMENT: Various quantities of polyacrylamide gel (Bio-Gel P4) were injected subcutaneously in the backs of mice. METHODS: Five hours after the injection of PAG the animals were euthanized, the injection sites lavaged and levels of LTB4, PGE2, TNF alpha and cells were determined. RESULTS: Subcutaneous injection of PAG caused a time-dependent response characterized by the accumulation of inflammatory cells peaking at 10 h and the formation of LTB4, PGE2 and TNF alpha, peaking at 5 h. PAG injection into W/Wv or SL/SLd mice (mice lacking mast cells) resulted in an attenuated response, i.e. LTB4 levels were reduced by 60% and minimal cell influx was seen. The lack of mast cells caused about a 30% reduction in the levels of TNF alpha found. CONCLUSIONS: These data suggest that mast cells play a prominent role in the PMN influx, TNF alpha production and eicosanoid formation in the PAG-induced inflammatory response.

Acrylic Resins↗
PubMed1998

Reduction of stress-induced analgesia following ethanol exposure in mice.

In the present study, we examined the effects of ethanol treatment on the subsequent expression of opioid and nonopioid forms of swim stress-induced analgesia (SSIA). In Experiment 1, mice were injected with ethanol (2.5 g/kg, i.p.) or an equal volume of saline once a day for two days. Animals received no treatment on day 3. On day 4, the animals were tested for opioid (3-min swim in water maintained at 32 degrees C) or nonopioid (3-min swim in water maintained at 20 degrees C) SSIA in the hotplate test (52 degrees C). Mice pretreated with ethanol injections showed a decrease in nonopioid SSIA, but not in opioid SSIA. In Experiment 2, mice were given an ethanol solution (10%) or tap water to drink for 15 days. On day 16, all animals were given tap water to drink. On day 17, the animals were tested for opioid or nonopioid SSIA. Neither form of SSIA was modified in mice that drank the ethanol solution. These results show that ethanol pretreatment can modify nonopioid endogenous analgesic responses in mice. Further, the route of administration influences the effects of ethanol pretreatment on SSIA.

Analgesia↗
PubMed1998

Tolerance to ethanol analgesia is not accompanied by cross-tolerance to morphine analgesia in rats.

In the present study, we examined the development of environment-independent and environment-dependent tolerance to ethanol-induced analgesia (EIA) and cross-tolerance with morphine-induced analgesia (MIA). To examine the development of environment-independent tolerance, male Long-Evans rats were given increasing amounts of ethanol (5 days each of 5% (v/v), 10% (v/v), and 15% (v/v)) added to their drinking water over a 15-day period. A control group was given plain tap water to drink. On day 16, all rats were given plain tap water to drink. On day 17, the animals were tested for EIA (2.5 g/kg, I.P.) or MIA (10 mg/kg, I.P.) in the hot plate test. To examine the development of environment-dependent tolerance, animals were injected with ethanol (2.5 g/kg, I.P.) or an equal volume of saline once a day for 2 days. On day 3, the animals received no treatment. On day 4, the animals were tested for either EIA (2.5 g/kg, I.P.) or MIA (10 mg/kg, I.P.) in the hot plate test. It was found that rats pretreated with ethanol (both self-administration and I.P. injections) displayed tolerance to EIA, which was not accompanied by cross-tolerance to MIA.

Analgesia↗
PubMed1997

Stimulus dependence of non-steroidal antiinflammatory drug potency in a cellular assay of prostaglandin H synthase-2.

The prostaglandin H synthase-2 selective non-steroidal antiinflammatory drugs nimesulide, NS-398 (N-(2-cyclohexyloxy-4-nitrophenyl)methanesulfonamide), flosulide and SC 58125 (5-(4-fluorophenyl)-1-[4-(methylsulfonyl)phenyl]-3-(trifluoromethyl)-1H- pyrazole) as well as the non-selective non-steroidal antiinflammatory drugs indomethacin, meclofenamate and ibuprofen were compared in a WISH (human amnionic epithelial cell) cellular assay of prostaglandin H synthase-2 activity. Varying amounts of prostaglandin E2 were induced in WISH cells using either interleukin-1beta, tumor necrosis factor-alpha or phorbol 12-myristate 13-acetate, alone or in combination, or with okadaic acid as stimulants. The results from these studies demonstrated that under conditions which generate greater amounts of prostaglandin E2, the potency of both prostaglandin H synthase-2 selective and non-selective non-steroidal antiinflammatory drugs may be reduced. Dexamethasone, a transcriptional inhibitor of prostaglandin H synthase-2, also became progressively less effective in cells activated by combinations of stimuli or with okadaic acid. We conclude that decreases in potency under conditions of high levels of prostaglandin H synthase-2 expression and prostaglandin E2 production are observed equally with prostaglandin H synthase-2 selective and non-selective inhibitors.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed1997

Structure-activity relationships of N-hydroxyurea 5-lipoxygenase inhibitors.

The discovery of second generation N-hydroxyurea 5-lipoxygenase inhibitors was accomplished through the development of a broad structure-activity relationship (SAR) study. This study identified requirements for improving potency and also extending duration by limiting metabolism. Potency could be maintained by the incorporation of heterocyclic templates substituted with selected lipophilic substituents. Duration of inhibition after oral administration was optimized by identification of structural features in the proximity of the N-hydroxyurea which correlated to low in vitro glucuronidation rates. Furthermore, the rate of in vitro glucuronidation was shown to be stereoselective for certain analogs. (R)-N-[3-[5-(4-Fluorophenoxy)-2-furyl]-1-methyl-2-propynyl]-N-hydroxyure a (17c) was identified and selected for clinical development.

Animals↗
PubMed1997

Effect of mast cell deficiency and leukotriene inhibition on the influx of eosinophils induced by eotaxin.

Eosinophils are believed to be important cells in the pathogenesis of asthma and allergic disease. Mast cells and leukotrienes may play a role in eosinophil recruitment. Eotaxin was recently described as a specific chemoattractant for eosinophils. Therefore we examined the effects of eotaxin on eosinophil flux in the mast cell-deficient WBB6F1/J-KitW/ KitW-v (W/Wv) mice and in mice treated with zileuton or ABT-761, specific 5-lipoxygenase inhibitors. Mice were injected intraperitoneally with eotaxin and at various times later the peritoneal cavities were lavaged and cell populations determined. Murine recombinant eotaxin induced a dose-dependent increase in eosinophils, which reached a maximum at 1-2 h and subsided at 4 h in both BALB/c and W/WV littermate control mice (no other cell population was altered). However, in eotaxin-injected W/Wv mice, the peak of eosinophil influx was delayed, peaking at 2 h, and a lower number of eosinophils was seen. The specific lipoxygenase inhibitors zileuton and ABT-761 given 30 min before eotaxin caused a 63-79% reduction in the level of eosinophils seen in the lavage fluid. These data suggest that eotaxin may either be activating eosinophils to release leukotrienes or making them more responsive to leukotrienes. In addition, mast cells may be playing a role in the amplification of the eotaxin effect.

Animals↗
PubMed1997

Synthesis of indolylalkoxyiminoalkylcarboxylates as leukotriene biosynthesis inhibitors.

A series of substituted indolylalkoxyiminoalkylcarboxylates were found to be potent leukotriene biosynthesis inhibitors. The structure-activity relationships were investigated. Representative potent inhibitors identified were the quinolyl 3a (A-86885) and pyridyl 3b (A-86886) congeners with in vitro IC50s of 21 and 9 nM and in vivo leukotriene inhibition in the rat with oral ED50s of 0.9 and 1.7 mg/kg, respectively.

5-Lipoxygenase-Activating Proteins↗
PubMed1997

Induction of prostaglandin H synthase-2 and tumor necrosis factor-alpha in human amnionic WISH cells by various stimuli occurs through distinct intracellular mechanisms.

These studies examined the signal transduction mechanisms by which prostaglandin (PG) E2 production can occur in human amnionic WISH cells in response to the stimuli okadaic acid, interleukin (IL)-1beta, tumor necrosis factor (TNF)-alpha, phorbol-12-myristate-13-acetate (PMA) or combinations of PMA with IL-1beta or TNF-alpha. We also investigated whether WISH cells are capable of producing TNF-alpha or IL-1beta in response to stimulation, because these cytokines can be produced in an autocrine fashion to perpetuate an inflammatory response. Our data indicate that the magnitude of PGE2 production induced by a given stimulus correlated temporally with the level of PGH synthase-2 (PGHS-2) protein. PMA or IL-1beta induced PGE2 production 2 to 4 hr after treatment, whereas the combination of these agents produced the most rapid induction 2 hr after treatment. Only okadaic acid induced the production of both PGE2 and TNF-alpha, after a lag of 12 to 18 hr. PGE2 production by all stimuli was inhibited by dexamethasone, the IL-1 receptor antagonist (IL-1ra), the specific PGHS-2 inhibitor NS-398 and the protein kinase inhibitor staurosporin. In contrast, TNF-alpha production in response to okadaic acid was inhibited by the TNF-converting enzyme inhibitor GI 129471 and staurosporin but was unaffected by either IL-1ra, dexamethasone or NS-398. We conclude that WISH cells are capable of producing bioactive proinflammatory mediators such as TNF-alpha and PGE2 through separable intracellular signal transduction mechanisms. The ability of IL-1ra to reduce PGE2 production caused by all stimuli used suggests an autocrine role for IL-1 in PGHS-2 induction in these cells.

Amnion↗
PubMed1997

ABT-761 attenuates bronchoconstriction and pulmonary inflammation in rodents.

Our primary goal has been to discover leukotriene biosynthesis inhibitors with characteristics that are appropriate for use as clinical agents. The success of the use of zileuton in the treatment of asthma led us to explore further the use of the N-hydroxyurea class of 5-lipoxygenase inhibitors as longer-acting compounds with good lung penetration. A variety of in vitro and in vivo methods were used to evaluate a large number of compounds, from which ABT-761 [(R)-N-(3-(5-(4-fluorophenylmethyl)thien-2-yl)-1-methyl-2-pr opynyl)-N-hydroxyurea] was selected for study. ABT-761 exhibited potent and selective inhibition of leukotriene formation both in vitro and in vivo. More importantly, the compound potently inhibited antigen-induced bronchospasm in guinea pigs when given either prophylactically or therapeutically. In addition, ABT-761 was a potent inhibitor of eosinophil influx into the lungs of Brown Norway rats. These data provide added support for the role of leukotrienes in both bronchospasm and eosinophilic inflammation and characterize ABT-761 as a particularly potent inhibitor of leukotrienes formed in pulmonary tissues. These data combined with the excellent pharmacokinetic characteristics of the compound indicate its potential use in the treatment of leukotriene-dependent human disease.

Animals↗
PubMed1997

Improving the in vivo duration of 5-lipoxygenase inhibitors: application of an in vitro glucuronosyltransferase assay.

An in vitro glucuronidation assay was used to optimize a series of N-hydroxyurea-containing 5-lipoxygenase inhibitors for metabolic stability. The glucuronidation of these compounds in cynomolgus monkey microsomes followed Michaelis-Menten kinetics allowing calculation of V(max) and K(M). The V(max) values ranged from 0.02 to 7.9 nmol/min/mg microsomal protein, a 400-fold difference, whereas K(M) ranged from 204 to 2500 microM, only a 12-fold difference. In vitro intrinsic clearance values (CL(int) were calculated for 18 compounds tested in the kinetic assay and compared with the in vivo plasma clearance (CL(p)) calculated from intravenous studies done in cynomolgus monkeys. These initial results suggested a relationship between the in vitro CL(int) and in vivo duration as defined by CL(p). A more rapid in vitro assay was developed in a 96-well format using a single concentration of substrate (100 microM) from which a glucuronidation rate was calculated. The results from this assay for 40 compounds correlated with in vivo plasma clearance (r = 0.57). This more efficient assay was used to test more than 100 compounds and develop structure-metabolism relationships based on metabolic stability and improved duration. The culmination of this effort contributed to the discovery of ABT-761, a 5-lipoxygenase inhibitor with in vivo duration in monkey improved 40-fold over thefirst generation inhibitor. Further studies performed in human liver microsomes demonstrated a similar trend that was corroborated by the 8-fold increase in duration after oral dosing in humans observed with ABT-761.

Animals↗
PubMed1996

Pharmacological modulation of eosinophil influx into the lungs of Brown Norway rats.

A model of lung inflammation was developed in Brown Norway rats. Intense lung eosinophilia was induced by a single intravenous injection of Sephadex G-200 particles. The eosinophilia observed was preceded by an increase in cysteinyl leukotrienes found in lung lavage fluids. Theophylline and albuterol were tested in the model and found to be inactive, while dexamethasone was effective. Zileuton, a specific leukotriene inhibitor, was found to effectively inhibit leukotriene formation and the influx of eosinophils into the lungs of these Sephadex-treated animals. Studies with specific leukotriene D4 antagonists of the cysLT1 type receptor indicate that this leukotriene receptor is probably not involved directly in the eosinophilic inflammation. This model appears to be useful in characterizing potential anti-inflammatory effects of inhibitors by evaluating their ability to prevent eosinophil influx into the lung.

Animals↗
PubMed1996

5-Lipoxygenase inhibitors: synthesis and structure-activity relationships of a series of 1-aryl-2H,4H-tetrahydro-1,2,4-triazin-3-ones.

Synthetic routes were developed to access a variety of novel 1-aryl-2H,4H-tetrahydro-1,2,4-triazin-3-one analogs which were evaluated as 5-lipoxygenase (5-LO) inhibitors. The parent structure, 1-phenylperhydro-1,2,4-triazin-3-one (4), was found to be a selective inhibitor of 5-LO in broken cell, intact cell, and human blood assays with IC50 values of 5-21 microM. In a rat anaphylaxis model, 4 blocked leukotriene formation with an ED50 = 7 mg/kg when administered orally. Compound 4 exhibited selectivity for inhibition of 5-LO with little activity against related enzymes: 12-LO from human platelets, 15-LO from soybean, and cyclooxygenase (COX) from sheep seminal vesicle. In pilot subacute toxicity testing, 4 did not produce methemoglobinemia in rats (400 mg/kg po daily for 9 days) or in dogs (200 mg/kg po daily for 28 days). These results indicated that the triazinone structure provided a 5-LO inhibitor template devoid of the toxicity problems observed in the related phenidone (1) and pyridazinone (3) classes of 5-LO inhibitors. The parent compound 4 is a selective, orally bioavailable 5-LO inhibitor which can serve as a useful reference standard for in vivo pharmacological studies involving leukotriene-mediated phenonmena.

Animals↗
PubMed1996

Leukotrienes do not regulate nitric oxide production in RAW 264.7 macrophages.

RAW 264.7 macrophages respond to lipopolysaccharide (LPS) and interferon-gamma (IFN-gamma) by producing large amounts of nitric oxide (NO) and prostaglandin E2 (PGE2), with maximal production 18-24 h after treatment. Following stimulation with the calcium inophore A23187, cultures of RAW cells also produce modest amounts of leukotrienes. However, the capacity of these cells to produce leukotrienes is transient, beginning 2 h after vehicle or LPS/IFN-gamma treatment, peaking by 4-6 h and absent by 8 h. A-79175, (R(+) N-[3-[5-(4-Fluorophenoxy)-2-furanyl]-1-methyl-2-propynyl]-N-hydroxyurea) a specific inhibitor of 5-lipoxygenase (5-LO), abolished leukotriene production by RAW cells in a dose-dependent, non-cytotoxic fashion while having no effect on PGE2 or NO production. By contrast, nordihydroguaiaretic acid (NDGA) inhibited production of leukotrienes, PGE2 and NO only at doses that were cytotoxic to the RAW cells. Exogenous leukotriene B4 (LTB4) had no effect on either NO or PGE2 production. An inhibitor of NO production, L-N-5-(1-iminoethyl) ornithine HCl (NIO) also did not affect leukotriene or PGE2 production, while dexamethasone blocked PGE2 and NO production, but did not affect leukotriene production in these cells. Taken collectively, these results indicate that there is no interaction between the pathways for leukotriene and nitric oxide production in RAW 264.7 macrophages.

Animals↗
PubMed1995

Clinical activity of leukotriene inhibitors.

Data from the emerging clinical trials with compounds such as zileuton, ICI 204,219, Bay X1005, MK571, MK679, and MK591 are demonstrating the importance of the leukotrienes as mediators of asthma and possibly other diseases such as rheumatoid arthritis, psoriasis, and inflammatory bowel disease. One of the major questions facing the asthma community is how much improvement in the FEV1 is needed to improve the quality of life of the asthmatic patient. Comparing the various approaches to asthma treatment, there is typically 15-20% improvement in the lung function with inhaled steroids. Leukotriene interventions apparently will improve lung function to similar levels as with inhaled steroids, and thus may offer an alternative to steroids. Like the steroids, zileuton appears to also reduce the inflammatory cell influx into the antigen-challenged site, which may have the long-term effect of reversing some of the tissue alterations that occur as a result of the inflammation seen with asthma. Importantly, the reported experience to date has shown that the leukotriene modulators do not have the same side-effects as the current therapies, and thus offer the hope that both safe and effective treatment may be derived from this approach. The clinical data reported do not yet define a preferred approach to the modulation of leukotriene pathology. As more studies are published in other diseases the broad spectrum use of these inhibitors will become known.

Anti-Inflammatory Agents↗
PubMed1995

Optimization of the potency and duration of action of N-hydroxyurea 5-lipoxygenase inhibitors.

As in vitro glucuronidation assay and several biochemical assays were utilized to discover potent new N-hydroxyurea-containing 5-lipoxygenase inhibitors with long durations of action. The best of these, A-78773, is a racemic mixture of two enantiomers. These enantiomers were purified and the R(+)-enantiomer A-79175 was found to be superior to the S(-)-enantiomer with respect to in vitro metabolism and duration of action in the monkey. A-79175 was a potent selective inhibitor of 5-hydroxyeicosatetraenoic acid formation in rat basophilic leukemic homogenates (IC50 = 54 nM) and of calcium ionophore-induced leukotriene B4 (LTB4) formation in purified human polymorphonuclear leukocytes (IC50 = 25 nM) and human whole blood (IC50 = 80 nM). The compound inhibited LT formation in the rat with oral ED50s of 1 to 2 mg/kg. It also was a potent inhibitor of edema and inflammatory cell influx in rats and mice. A-79175 was resistant to glucuronidation and had an elimination half-life of nearly 9 hr in cynomolgus monkeys. A-79175 inhibited ex vivo LTB4 formation by monkeys for extended periods. A single 0.5-mg/kg oral dose gave > 50% inhibition of calcium ionophore-induced LTB4 formation ex vivo for 12 hr. A good correlation was found between the elimination half-life for A-78773 and its enantiomers in cynomolgus monkeys and humans. These data indicate that A-79175 is a promising long-acting agent that should be useful to delineate the importance of LTs in animal and human studies.

Animals↗