PubMed Health⌕ Search

Biomedical subjects

A Ford-Hutchinson

Publications and source records attributed to A Ford-Hutchinson.

14 recordsLinked to original sources
PubMed2000

Membrane-associated proteins in eicosanoid and glutathione metabolism (MAPEG). A widespread protein superfamily.

The members of the MAPEG superfamily have been aligned and found to be distantly related, with a common pattern of hydropathy. Figure 2A shows the multiple sequence alignments of the human members and Figure 2B the corresponding superimposed hydropathy profiles. The alignment in Figure 2A demonstrates a total of six strictly conserved residues. The Arg-51 in LTC4 synthase has been suggested to function as proton donor for the opening of the LTA4 epoxide. This arginine is found in all but the FLAP sequences in accordance with the observation that FLAP has no known enzyme activity. Also the Tyr-93 in LTC4 synthase has been suggested to function as a base for the formation of the thiolate anion of glutathione. This tyrosine is not conserved in MGST1 or MGST1-L1. Table 1 summarizes some other properties of the individual human proteins. They are all of the same size, ranging from 147 to 161 amino acids. Only FLAP differs in that its isoelectric point is more neutral than that of the other, more basic proteins. The genes encoding these proteins all reside on different chromosomes (when known) (Table 1). In addition to the human proteins, MAPEG members have been identified in plants, fungi, and bacteria. It is clearly a challenge to elucidate their role in these different phyla in relation to their defined physiological functions in humans.

Amino Acid Sequence↗
PubMed1999

Common structural features of MAPEG -- a widespread superfamily of membrane associated proteins with highly divergent functions in eicosanoid and glutathione metabolism.

A novel superfamily designated MAPEG (Membrane Associated Proteins in Eicosanoid and Glutathione metabolism), including members of widespread origin with diversified biological functions is defined according to enzymatic activities, sequence motifs, and structural properties. Two of the members are crucial for leukotriene biosynthesis, and three are cytoprotective exhibiting glutathione S-transferase and peroxidase activities. Expression of the most recently recognized member is strongly induced by p53, and may therefore play a role in apoptosis or cancer development. In spite of the different biological functions, all six proteins demonstrate common structural characteristics typical of membrane proteins. In addition, homologues are identified in plants, fungi, and bacteria, demonstrating this superfamily to be generally occurring.

Amino Acid Sequence↗
PubMed1995

Inhibition of leukotriene biosynthesis improves renal function in experimental glomerulonephritis.

The development of renal dysfunction in experimental glomerulonephritis (GN) is mediated in part by enhanced leukotriene (LT) formation. In our studies the pathophysiological role of LTs was investigated through pharmacological inhibition of LT biosynthesis in a rat model of nephrotoxic serum nephritis. MK-0591, an indirect inhibitor of 5-lipoxygenase activity, was co-administered to rats injected with nephrotoxic rabbit serum, followed by assessment of renal function, morphology and microsomal LTC4 synthase activity on day 7. A significant improvement in glomerular function was noted (p < 0.05), together with a 50% reduction in proteinuria (p < 0.01) in animals receiving MK-0591 (60 mg kg-1 day-1). In addition, the fall in renal LTC4 synthase activity which occurred in nephritic rats (to 74% of control values, p < 0.01) was prevented in drug-treated animals. Based on these results, it appears that inhibition of LT biosynthesis protects against both renal impairment and alterations in LTC4 synthase activity during the development of experimental GN, and may provide a useful therapeutic adjunct in the treatment of this disease.

5-Lipoxygenase-Activating Proteins↗
PubMed1995

Levels of peptidoleukotriene E4 are elevated in active Crohn's disease.

Proinflammatory mediators, including leukotriene (LT) B4, are elevated in the intestinal mucosa in active chronic inflammatory bowel diseases (IBD). LTE4 is the major peptidoleukotriene metabolite and it is stable in urine. The aim of this study was to measure LTE4 levels in the urine of 27 children with Crohn's disease and 27 control subjects including 12 children with functional recurrent abdominal pain and 15 unaffected siblings of IBD patients. LTE4 levels were measured in urine using high-performance liquid chromatography separation and radioimmunoassay with specific antibody. The Pediatric Crohn's Disease Activity Index and physician global assessment were used to categorize patient groups. C-reactive protein, orosomucoid, and erythrocyte sedimentation rate were employed as laboratory markers of mucosal inflammation. Urinary LTE4 levels were elevated in the 13 children with active Crohn's disease (160.5 +/- 59.4 pg/ml; mean +/- SEM) compared with both levels in the 14 patients with inactive disease (67.1 +/- 18.1 pg/ml; p < 0.05) and controls (45.0 +/- 10.9 pg/ml; p < 0.05). We conclude that measurement of urinary LTE4 is a useful test for monitoring the activation of peptidoleukotrienes in patients with Crohn's disease. It provides a noninvasive, objective adjunct for assessment of disease activity and could be employed in future trials examining the role of the leukotriene inhibitors in the medical therapy of IBD.

Acute Disease↗
PubMed1994

Effect of FLAP antagonist MK-0591 on leukotriene production and ozone-induced airway responses in dogs.

We used the 5-lipoxygenase-activating protein (FLAP) antagonist MK-0591 to investigate the importance of leukotrienes (LT) in causing ozone-induced bronchoconstriction, airway inflammation, and airway hyperresponsiveness in dogs. Six random source dogs were studied. On one day, dogs were treated with MK-0591 (2 mg/kg iv) followed by a continuous intravenous infusion of 8 micrograms.kg-1.min-1. On the other day, the diluent was infused. Acetylcholine airway responsiveness was measured before and 1 h after ozone inhalation (3 ppm for 30 min). On each day, whole blood and bronchoalveolar lavage (BAL) cells were challenged with calcium ionophore to stimulate LTB4 production. Urinary LTE4 levels were measured before and after ozone. MK-0591 inhibited LTB4 production in whole blood by 96% (P = 0.001) and that from BAL cells by 91% (P = 0.001). By contrast, MK-0591 had no effect on ozone-induced bronchoconstriction, airway hyperresponsiveness, or influx of neutrophils into BAL. The mean log difference of the pre- to post-acetylcholine provocative concentration was 0.64 +/- 0.40 during MK-0591 treatment and 0.68 +/- 0.40 during diluent treatment (P = 0.71). These results indicate that peptidoleukotrienes are produced during ozone inhalation and that MK-0591 inhibits LT production in dogs. However, LTs do not play a role in ozone-induced bronchoconstriction, airway inflammation, or airway hyperresponsiveness in dogs.

5-Lipoxygenase-Activating Proteins↗
PubMed1993

Assessment of the in vivo biochemical efficacy of orally active leukotriene biosynthesis inhibitors.

In man, the therapeutic effectiveness of specific inhibitors of leukotriene (LT) biosynthesis against allergen-induced bronchoconstriction appears to be related to the in vivo biochemical efficacy of these compounds, as measured by inhibition of whole blood LTB4 generation (upon A23187 stimulus) and, particularly, urinary LTE4 excretion. Accordingly, we have assessed the ability of two clinically documented LT biosynthesis inhibitors, zileuton and MK-886, and the structurally novel 5-lipoxygenase activating protein antagonist, MK-0591, to inhibit the production of these inflammatory arachidonic acid metabolites in laboratory dogs. Zileuton (2 mg/kg) was extremely bioavailable in dogs (> 10 microM plasma concentrations), and inhibited the A23187-induced ex vivo production of LTB4 by venous blood by > 90%, in concordance with its potency in canine blood in vitro (IC50 = 1.1 microM). Despite this degree of inhibition in whole blood, urinary LTE4 excretion was reduced by only 52%, a profile of activity similar to that seen in clinical studies. MK-886 was less well absorbed, with plasma concentrations of 3 microM being achieved only at 25 mg/kg. These levels resulted in < 45% inhibition of LTB4 production, but a significant (p < 0.05) 47% inhibition of urinary LTE4 excretion. MK-0591 was similarly bioavailable (compared with MK-886), but 10-fold more active in vivo as a 2 mg/kg dose resulted in 41-62% inhibition of urinary LTE4 excretion (p < 0.05 vs controls; n = 4, 28). Significant inhibition of ex vivo LTB4 synthesis was also observed at this dose (49%), in accord with peak plasma concentrations of 0.5 microM and an in vitro potency of 0.2-0.4 microM (IC50) in whole blood from these animals. At higher dose (10 mg/kg), MK-0591 inhibited LTE4 excretion by 69%, with 88% inhibition of the LT biosynthetic capacity of whole blood. These data demonstrate that the biochemical efficacy of structurally diverse leukotriene biosynthesis inhibitors can be assessed in vivo in normal laboratory dogs. Such measurements, combined with bioavailability data from other species, may be useful for predicting biochemical activity in man.

Animals↗
PubMed1993

Leukotriene generation and metabolism in dogs: inhibition of biosynthesis by MK-0591.

Peptidoleukotriene metabolism in dogs was investigated to determine the suitability of this species for the development of in vivo biochemical models of asthma and inflammation. Circulatory metabolism of [3H]leukotriene (LT)C4 (0.5 microCi/kg, i.v.) to [3H]LTE4 and subsequent clearance was rapid (T1/2 = 100 sec). After 3 h, the major urinary metabolite was [3H]16-carboxydihydrotetranor LTE4 (identified by radiochromatography), with [3H]LTE4 accruing to a significant 1.7 +/- 0.9% (n = 3) of the original [3H]LTC4 dose. Immunoreactive LTE4 was excreted into canine urine at 1.85 +/- 0.35 to 2.35 +/- 0.57 ng/h (n = 4) over a 6-h period, suggesting that this metabolite may be an index of acute in vivo 5-lipoxygenase activity. MK-0591, a high-affinity ligand for the canine homolog of the human 5-lipoxygenase activating protein, dose-dependently inhibited the systemic generation of peptidoleukotrienes as measured by urinary LTE4 excretion (ED50 1 microgram/kg/min), the time course of disappearance of LTE4 from the urine being similar to that of the clearance of [3H]LTE4. Because the therapeutic improvements in human allergic asthmatics treated with LT synthesis inhibitors and challenged with antigen appear to be related to the degree of in vivo inhibition of LT biosynthesis (measured by urinary LTE4), the dog may be an appropriate species for preclinical assessment of LT inhibitors.

5-Lipoxygenase-Activating Proteins↗
PubMed1990

Eosinophil-eicosanoid interactions: inhibition of eosinophil chemotaxis in vivo by a LTD4-receptor antagonist.

Chemotaxis of guinea-pig eosinophils in vivo has been studied in the guinea-pig conjunctiva. Guinea-pig eosinophils were labelled with 111In oxine and injected i.v. into recipient animals. Circulating radioactivity remained constant over a period of 4 h but dropped transiently in response to a bolus injection (1 nmol) of platelet activating factor (PAF), suggesting that the 111In-labelled eosinophils had retained their responsiveness to PAF. Leukotriene D4 (LTD4, 1 nmol/eye) and PAF (10 nmol/eye), but not histamine (5 nmol/eye), induced a significant 2.5-fold increase in conjunctival radioactivity, a measure of eosinophil chemotaxis in vivo, after 17 h. Antigen challenge (250 micrograms/eye) in ovalbumin-sensitized animals produced larger responses (8-fold increases) at the same time point. A specific LTD4 receptor antagonist MK-571 (10 micrograms/eye) completely inhibited in vivo chemotactic responses to LTD4, and partially inhibited (54%) the responses to ovalbumin (observations subsequently confirmed by histological studies). As eosinophils may play an important role in allergic diseases, the results with MK-571 indicate that selective and potent LTD4 receptor antagonists may provide a novel therapy for allergic conjunctivitis, rhinitis and asthma.

Animals↗
PubMed1990

Application of reversed phase high performance liquid chromatography to the analysis of sulphidopeptide leukotrienes in pig bile.

Reversed phase HPLC methodology has been developed for separation of peptide leukotrienes and indomethacin in porcine bile. Reproducible recoveries were obtained using radioactive leukotrienes ([3H]LTC4, 57.1 +/- 2.5%; [3H]LTE4, 62.7 +/- 1.9%; [3H]LTD4, 54.3 +/- 2.7%). Radioimmunoassay of column eluant demonstrated that as little as 300 pg of exogenous leukotrienes could be measured in bile fluids, with similar recoveries. Analysis of bile sampled 60-90 min after initiation of experimental endotoxic shock in indomethacin treated pigs revealed a leukotriene concentration of 5.24 +/- 1.16 ng/mL(LTD4). This was significantly greater (p less than 0.05, n = 3) than that observed in samples collected prior to endotoxin (0.42 +/- 0.23 ng/mL), or from untreated animals (0.85 +/- 0.51 ng/mL). This method is thus applicable to investigation of the role of 5-lipoxygenase products in porcine models of human disease, including shock conditions such as endotoxaemia, during cyclooxygenase inhibition by indomethacin.

Animals↗
PubMed1986

Biological actions of leukotrienes. State of the art lecture.

Leukotrienes are novel mediators derived from arachidonic acid through the 5-lipoxygenase enzyme system. Leukotriene B4 has potent effects on leukocyte function and in vivo induces leukocyte accumulation and changes in vascular permeability and modulates pain responses. Peptido-lipid leukotrienes are potent smooth muscle--contracting agents. They may have important cardiovascular actions through mechanisms involving either vasoconstriction or indirect vasodilatation. Evidence for leukotriene production has been found in subjects with allergic conditions and psoriasis, indicating a putative role for these substances in human disease.

Animals↗
PubMed1985

Potentiation of the inhibitory effect of a thromboxane A2 antagonist (L-640,035) on arterial thrombosis formation in rabbit by the angiotensin converting enzyme inhibitor enalapril.

The angiotensin converting enzyme inhibitor enalapril (0.5 mg/kg i.v.) potentiated significantly the inhibitory effect of the thromboxane A2 antagonist L-640,035 (1 mg/kg i.v.) on electrically induced platelet accumulation in the rabbit in vivo. Enalapril had no effect upon platelet accumulation when given alone. The hypotensive effects of enalapril did not account for the potentiation because a combination of hexamethonium (5 mg/kg i.v.) and hydralazine (1 mg/kg i.v.), which decreased blood pressure similarly to enalapril, did not augment the effect of L-640,035. Determination by radioimmunoassay of plasma levels of immunoreactive 6-keto-PGF1 alpha, suggested that increases in PGI2 levels after combined administration of enalapril and L-640,035 could explain the observed potentiation.

6-Ketoprostaglandin F1 alpha↗
PubMed1985

Effects of synthetic leukotrienes on local blood flow and vascular permeability in porcine skin.

The local effects of synthetic leukotrienes (LT) were examined in the skin of the anesthetized pig. Blood flow was measured noninvasively with the use of a laser-Doppler flow meter and changes in vascular permeability were measured using technetium-labeled human serum albumin as a marker for extravasation. LTB4 and the peptidolipid leukotrienes, LTC4, LTD4, LTE4, LTF4, induced vasodilator responses when injected intradermally at a dose of 1 ng. The vasodilator effects of LTB4 and LTF4 were comparable in magnitude to those of prostaglandin E2 (PGE2) and histamine and persisted over a wide dose range. Vascular permeability was induced by histamine, PGE2, and LTB4 but not by the other leukotrienes. The effects of LTB4 were significantly increased in the presence of PGE2. Leukotrienes appear not to produce their effects through the generation of prostaglandins as neither the vasodilator nor the permeability-enhancing effects were affected by treatment with indomethacin. The present investigation demonstrates that the pig is the first animal model to be described which reflects the potent vasodilator actions of leukotrienes in human skin. The porcine skin may thus be a useful model in the study of human skin diseases.

Animals↗
PubMed1978

Radioisotope scanning using a gamma camera.

Sixteen outpatients with rheumatoid arthritis took part in a placebo controlled double-blind crossover study. In addition to conventional measurements, a radioactive index was measured using a gamma camera that indicated a radioactive count over the measured joints and a comparable area of normal adjacent bone. This index showed poor correlation with other conventional measurements of change in the clinical trial.

Arthritis, Rheumatoid↗