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R Hyland

Publications and source records attributed to R Hyland.

At least 19 recordsLinked to original sources
PubMed2003

Evaluation of the role of the asialoglycoprotein receptor in the clearance of UK-279,276 (recombinant neutrophil inhibitory factor).

1. UK-279,276 or recombinant neutrophil inhibitory factor (rNIF) is a glycoprotein that has been investigated as an intravenous treatment for stroke. Previous data indicate that the asialoglycoprotein receptor (ASGPR) in the liver might have a role in the uptake and clearance of UK-279,276 from plasma in rats and dogs. 2. Biliary elimination of sialo UK-279,276 can be inhibited by the co-administration of asialo fetuin, a known substrate for ASGPR. These data are in keeping with sialo UK-279,276 being cleared by ASGPR. 3. In vitro experiments have demonstrated that asialo UK-279,276 (Sialo UK-279,276 treated to remove the sialic acid residues present on the glycans) shows a significantly greater uptake in rat, dog and human precision-cut liver slices than the sialylated protein. The addition of asialo fetuin to precision-cut liver slice incubations (rat, dog and man) containing asialo UK-279,276 reduced the uptake to levels similar to those seen for the sialylated protein. These data support the potential role of the ASGPR in the clearance of UK-279,276 in rat, dog and man.

Animals↗
PubMed2003

Identification of the cytochrome P450 enzymes involved in the N-oxidation of voriconazole.

Voriconazole is a triazole antifungal agent with potent activity against a broad spectrum of clinically significant pathogens. In vivo and in vitro studies have demonstrated that voriconazole is extensively metabolized, with the major circulating metabolite resulting from N-oxidation. In the present study, we report on the human cytochrome P450 enzymes responsible for the generation of this metabolite. In human liver microsomes voriconazole N-oxidation exhibited biphasic kinetics with K(m1) of 8.1 microM, and K(m2) of 835 microM. Studies at 2500 microM voriconazole identified CYP3A4 as the low-affinity component, with activity correlating strongly with CYP3A4 activity in a bank of human liver microsomes (r = 0.90) and inhibited by ketoconazole. At 25 microM, voriconazole N-oxidation showed strong correlation with CYP2C19 and CYP3A4 activity (r = 0.77 and 0.74, respectively) and was inhibited by both sulfaphenazole and ketoconazole. Incubations with recombinant enzymes suggested both CYP2C9 and CYP2C19 as high-affinity enzymes (K(m) values of 20 and 3.5 microM, respectively). Further studies used chemical inhibitors in human liver microsomes prepared from individual donors, including two CYP2C19 poor metabolizers. No inhibition was observed with sulfaphenazole, indicating a minor role for CYP2C9 in human liver, but inhibition by ketoconazole was most potent in the CYP2C19 poor metabolizer livers, suggesting an increased role for CYP3A4 in individuals lacking CYP2C19. These data indicate that voriconazole is a substrate for CYP2C9, CYP2C19, and CYP3A4, with CYP2C9 involvement being minimal in human liver microsomes. Genotype status for CYP2C19 and/or coadministration of drugs that modulate CYP2C19 or CYP3A4 activities could effect voriconazole plasma levels.

Antifungal Agents↗
PubMed2001

Identification of the cytochrome P450 enzymes involved in the N-demethylation of sildenafil.

AIMS: To characterize the cytochrome P450 (CYP) enzymes responsible for the N-demethylation of sildenafil to its main metabolite, UK-103 320, to investigate the potential inhibitory effects of sildenafil on CYP enzymes and to evaluate the potential of selected drugs to affect sildenafil metabolism. METHODS: The metabolic pathways of sildenafil N-demethylation were studied using human liver microsomes, as well as microsomes expressing individual human CYP enzymes. Further studies to identify the individual enzymes were performed at 2.5 and 250 microM sildenafil, and employed a combination of chemical inhibition, correlation analysis, and metabolism by expressed recombinant CYP enzymes. In addition, the effect of sildenafil on the activity of the six major drug metabolizing enzymes was investigated. RESULTS: Sildenafil conversion was found to be mediated by at least two CYP enzymes, for which the mean kinetic parameters were Km1 = 6(+/-3 microM), Km2 = 81(+/-45 microM), Vmax1 = 22(+/-9 pmol) and Vmax2 = 138(+/-77 pmol) UK-103 320 formed min(-1) mg(-1). At 250 microM sildenafil, N-demethylation was primarily mediated through the low-affinity, high-Km enzyme (approximately 83%), whilst at 2.5 microM there was a greater role for the high-affinity, low-Km enzyme (approximately 61%). Ketoconazole strongly inhibited metabolism at both sildenafil concentrations and was the only significant inhibitor at 250 microM sildenafil. At the lower sildenafil concentration, sulphaphenazole and quinidine also inhibited formation of UK-103 320. Overall, 75% or more of the N-demethylation of sildenafil at any concentration is probably attributable to CYP3A4. These results were supported by experiments using expressed human CYP enzymes, in which only CYP3A4 and CYP2C9 exhibited substantial sildenafil N-demethylase activity (respective Km values of 221 microM and 27 microM). Sildenafil metabolism was inhibited by potent CYP3A4 inhibitors which are used clinically, but was found to be only a weak inhibitor of drug metabolizing enzymes itself, the strongest inhibition occurring against CYP2C9 (Ki = 80 microM). CONCLUSIONS: Evidence is provided for CYP3A4 and to a lesser extent CYP2C9-mediated metabolism of sildenafil. There is the possibility that elevated plasma concentrations of sildenafil could occur with coadministration of known inhibitors of CYP2C9 or CYP3A4. Since peak plasma concentrations of clinical doses of sildenafil are only 200 ng ml(-1) ( approximately 0.4 microM) it is very unlikely that sildenafil will significantly alter the plasma concentration of other compounds metabolized by cytochrome P450 enzymes.

Aryl Hydrocarbon Hydroxylases↗
PubMed2000

The initiator element of the Drosophila beta2 tubulin gene core promoter contributes to gene expression in vivo but is not required for male germ-cell specific expression.

The tissue-specific expression of the Drosophila beta 2 tubulin gene ( B2t ) is accomplished by the action of a 14-bp activator element (beta2UE1) in combination with certain regulatory elements of the TATA-less, Inr-containing B2t core promoter. We performed an in vivo analysis of the Inr element function in the B2t core promoter using a transgenic approach. Our experiments demonstrate that the Inr element acts as a functional cis -regulatory element in vivo and quantitatively regulates tissue-specific reporter expression in transgenic animals. However, our mutational analysis of the Inr element demonstrates no essential role of the Inr in mediating tissue specificity of the B2t promoter. In addition, a downstream element seems to affect promoter activity in combination with the Inr. In summary, our data show for the first time the functionality of the Inr element in an in vivo background situation in Drosophila.

Animals↗
PubMed2000

Human hepatocytes in primary culture predict lack of cytochrome P-450 3A4 induction by eletriptan in vivo.

Eletriptan (Relpax) is a novel 5-hydroxytryptamine (serotonin)(1D/1B) agonist currently in development for the acute treatment of migraine. The aim of this work was to evaluate the relative induction potency of eletriptan in vitro compared with well characterized cytochrome P-450 (CYP) inducers with primary cultures of human hepatocytes and to relate this to the situation in vivo. Eletriptan was a weak inducer of CYP3A4 protein and cyclosporin A oxidation in four of the six cultures used, whereas rifampicin was a potent inducer in all cultures. Induction was concentration dependent and not detectable at eletriptan concentrations of 5 microM and lower. The amplitude of the increase in CYP3A4 protein and activity by 25 microM eletriptan was significantly lower, with a mean of 19 (P =.0015) and 26% (P =.0002), respectively, of that observed in response to 25 microM rifampicin. CYP2A6, a protein with minor pharmacological implication, also was induced by eletriptan and rifampicin in two cultures but was not detected in the others. The levels of other CYP proteins, including CYP1A2, CYP2C9, CYP2C19, CYP2D6, and CYP2E1, were not affected by eletriptan. Because the maximum blood concentration of eletriptan in humans after a therapeutic dose (maximum 80 mg) is 0.5 microM, the in vitro model would predict no clinically significant induction of CYP3A4 protein in vivo. This has been confirmed subsequently in a clinical study, with 6beta-hydroxycortisol/cortisol ratios as marker of CYP3A4 activity. Eletriptan is therefore not an inducer of CYP3A4 at clinical doses.

Adult↗
PubMed1998

Interaction of terfenadine and its primary metabolites with cytochrome P450 2D6.

The substrate structure-activity relationships described for the major human drug-metabolizing cytochrome P450 (P450 or CYP) enzymes suggest that the H1 receptor antagonist terfenadine could interact with CYP2D6 either as a substrate or as an inhibitor, in addition to its known ability to act as a substrate for CYP3A4. Based on this substrate structure-activity relationship, computer modeling studies were undertaken to explore the likely interactions of terfenadine with CYP2D6. An overlay of terfenadine and dextromethorphan, a known substrate of CYP2D6, showed that it was possible to superimpose the site of hydroxylation (t-butyl group) and the nitrogen atom of terfenadine with similar regions in dextromethorphan. These observations were substantiated by the ease of docking of terfenadine into a protein model of CYP2D6. Experimentally, terfenadine inhibited CYP2D6 activity in human liver microsomes with an IC50 of 14-27 microM, depending on the CYP2D6 substrate used. The inhibition of CYP2D6 was further defined by determining the Ki for terfenadine against bufuralol 1'-hydroxylase activity in four human livers. Terfenadine inhibited bufuralol 1'-hydroxylase activity with a Ki of approximately 3.6 microM. The formation of the hydroxylated metabolite (hydroxyterfenadine) in microsomes prepared from human liver and specific P450 cDNA-transfected B lymphoblastoid cells indicated that only CYP2D6 and CYP3A4 were involved in this transformation. As expected, the rate of formation was greatest with CYP3A4 (Vmax = 1257 pmol/min/nmol of P450), with CYP2D6 forming the metabolite at a 6-fold lower rate (Vmax = 206 pmol/min/nmol of P450). The two enzymes had similar KM values (9 and 13 microM, respectively). These data indicate that, as predicted from modeling studies, terfenadine has the structural features necessary for interaction with CYP2D6.

Chromatography, High Pressure Liquid↗
PubMed1996

Perindopril treatment prevents the loss of endothelial nitric oxide function and development of neo-intima in rabbits.

An atheroma-like neo-intima was produced by positioning a flexible collar around the common carotid arteries of normocholesterolaemic rabbits. Vessel segments taken from the mid-region of the collared and control region of the same artery were studied 7 days after surgery. Placebo rabbits were provided ab libitum with regular tap water, and treated animals were supplied with water containing perindopril (0.3 mg/kg/day) for 14 days. Perindopril treatment reduced plasma angiotensin converting enzyme (ACE) activity by 88%, but did not significantly alter arterial blood pressure or heart rate. In control rings from placebo rabbits perindoprilat in vitro (0.1-1.0 microM) reduced the sensitivity to angiotension I up to 20-fold but did not affect that of angiotensin II. In placebo rabbits, the collared arterial segments were approximately five-fold more sensitive to the vasoconstrictor action of 5-HT (P < 0.05) than the corresponding control segments. Perindopril treatment did not prevent the supersensitivity of the collared vessels to 5-HT. Development of the lesion in placebo or perindopril-treated rabbits did not alter the vascular sensitivity to either angiotensin I (10(-9)-10(-5)M) or angiotensin II (10(-10)-10(-6)M). The vasorelaxant action of sodium nitroprusside was similar in collared and control rings, whereas the maximum endothelium-dependent vasorelaxant response to acetylcholine was reduced from 68 +/- 5% in control rings, to 44 +/- 8% (mean +/- S.E.M., n = 9, P < 0.05) in collared rings of placebo-treated rabbits. In the perindopril-treated animals, this impairment of relaxation was restored in collared vessels and was no longer significantly different from the control sections. In contrast, perindoprilat in vitro (1.0 microM) did not alter the vasorelaxant response to acetylcholine in control or collared rings in a separate series of placebo rabbits. Morphologically, vessel segments taken from the centre of the collared artery of all placebo rabbits showed a thickened intima filled with cells that had the appearance of synthetic-state smooth muscle. The intimal/medial cross-sectional area ratio was reduced from 0.11 +/- 0.02 (n = 10) in placebo rabbits to 0.05 +/- 0.01 (n = 9) in perindopril-treated rabbits, whereas cross-sectional area of media of the collared vessels was similar in the two groups. Thus ACE may have important roles in the initiation and progression of atheroma-like lesions. Inhibition of ACE with perindopril reduces intimal thickening and restores the defective vasodilatation induced by the endothelial-dependent vasodilator, acetylcholine.

Angiotensin II↗
PubMed1996

Significance of metabolism in the disposition and action of the antidysrhythmic drug, dofetilide. In vitro studies and correlation with in vivo data.

Dofetilide, a class III antidysrhythmic agent, undergoes both renal and metabolic clearance. Characterization of the metabolism in vitro allows explanation of species differences, whereas identification of the human enzymes involved permits assessment of potential drug interaction. In liver microsomes, the rate of oxidative metabolism of dofetilide is in the order: male rat > female rat > dog > humans, which correlates with the metabolic clearance seen in vivo. In vitro products of oxidative metabolism, formed by N-dealkylation, are the same as those formed in vivo, with the N-desmethyl being the major product. This route of dofetilide metabolism is mediated by cytochrome P450 (CYP). In humans, N-demethylation has a high KM of 657 +/- 116 microM, indicating low affinity for the enzyme's active site. In a number of human liver microsomal preparations, this rate correlated (r = 0.903) with the activity of CYP3A4. There was no correlation with the activities of other isozymes. Specific isozyme inhibitors also indicated the involvement of CYP3A4, with partial inhibition being observed with ketoconazole and troleandeomycin, whereas the activator, alpha-naphthaflavone, caused increased turnover. No inhibition was observed with specific inhibitors or competing substrates for other isozymes. Dofetilide did not significantly inhibit CYP2C9, CYP2D6, or CYP3A4 at concentrations up to 100 microM in vitro. In contrast, amiodarone (IC50, 25 microM) and flecainide (49 microM) inhibited CYP2C9 and quinidine (0.26 microM), and flecainide (0.44 microM) inhibited CYP2D6. Many antidysrhythmic drugs have active, circulating metabolites, complicating the relationship of dose and clinical response. In vitro pharmacology studies allow assessment of the potential contribution to the pharmacological profile by metabolites. Potency of dofetilide and metabolites has been compared for class III (K+ channel blockade) and class I (Na+ channel blockade) antidysrhythmic activities. Three of the metabolites of dofetilide displayed class III activity, but at concentrations at least 20-fold higher than dofetilide. Dofetilide N-oxide showed class I activity, but only at high concentration. Neither resting membrane potential or action potential amplitude were affected by any metabolite. This lack of biologically relevant activity is in accord with the close correlation between plasma concentrations of dofetilide and pharmacological response.

Action Potentials↗
PubMed1995

Angiotensin-converting enzyme inhibitors reduce neointimal thickening and maintain endothelial nitric oxide function in rabbit carotid arteries.

Application of periarterial collars induced atheroma-like lesions in the carotid arteries of normocholesterolemic rabbits. Vessel segments taken from the mid-region of the collar (cuffed region) and control regions of the same artery were studied at 7 days after surgery. A group of placebo rabbits was provided ad libitum with regular tap water, and treated animals were supplied for 14 days (beginning 7 days before collar application) with water containing perindopril (daily intake of approximately 0.3 mg/kg). Perindopril treatment reduced plasma angiotensin-converting enzyme (ACE) activity by 88% but did not significantly alter arterial blood pressure or heart rate. The sensitivity of arterial rings to angiotensins I and II did not differ between control and cuffed arteries in either placebo or perindopril-treated rabbits, but in rings from both groups of rabbits the sensitivity to the vasoconstrictor action of serotonin was higher in the cuffed segments, as in previous studies. In addition, in placebo rabbits the endothelium-dependent vasorelaxant response to acetylcholine (which results from the release of nitric oxide) was weaker in cuffed arteries than in controls, whereas in the perindopril-treated animals, this impairment of relaxation was restored to the extent that, in cuffed vessels, it was no longer significantly different from the controls. Similar results were obtained in rabbits treated with another ACE inhibitor (ramipril). In contrast, acute treatment with the metabolite, perindoprilat, in vitro (1.0 microM) did not alter the response to acetylcholine in control or cuffed rings from placebo rabbits. Morphologically, vessel segments taken from the center of the cuffed artery of placebo rabbits showed a thickened intima with marked smooth muscle cell proliferation.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1994

International comparison of cave radon concentrations identifying the potential alpha radiation risks to British cave users.

Elevated concentrations of 222Rn have been recorded in many limestone caves throughout the world. As prolonged exposure to high radon concentrations has been linked to cancer and tumors, particularly of the lung (National Academy of Science 1988; Eatough and Henshaw 1990), a national survey of radon in British caves was undertaken. Passive radon detectors were exposed at 250 sites in 47 caves over four 7-d sampling periods. Mean concentrations ranging from 454-8,868 Bq m-3 were recorded. In one system, in the Peak District, radon concentrations of 155,000 Bq m-3 were recorded. The results indicate that the potential radiation dose from a single 4-h trip could exceed the national average annual background radiation dose (for the UK) from radon of 1.25 mSv.

Air↗
PubMed1992

Metabolic oxidation and toxification of N-methylformamide catalyzed by the cytochrome P450 isoenzyme CYP2E1.

Alkylformamides, for example N-methylformamide, are hepatotoxic in rodents and humans. The mechanism by which N-methylformamide exerts its hepatotoxicity involves metabolic oxidation at the formyl moiety to yield a short-lived intermediate, perhaps methyl isocyanate, which reacts with glutathione to afford S-(N-methylcarbamoyl)glutathione. The hypothesis that the cytochrome P450 isozyme CYP2E1 catalyzes the metabolic toxification of N-methylformamide was tested. Hepatocytes obtained from mice that had received acetone, an inducer of CYP2E1, were incubated for up to 4 hr with N-methylformamide (5 and 10 mM). Whereas N-methylformamide caused cytotoxicity in these cells, as measured by release from the cells of lactate dehydrogenase, it was barely toxic, under these conditions, to cells from untreated mice. Coincubation of N-methylformamide with dimethylsulfoxide (10 mM), a CYP2E1 inhibitor, for 4 or 6 hr abolished the hepatocytotoxicity of N-methylformamide. Metabolism of N-methylformamide to S-(N-methylcarbamoyl) glutathione was measured in incubates with liver microsomes from rats, mice, or humans in the presence of glutathione. Pretreatment of rodents with acetone or ethanol induced the rate of metabolism of N-methylformamide and of p-nitrophenol, a known CYP2E1 substrate, but it did not increase aminopyrine N-demethylation. Metabolism of N-methylformamide and p-nitrophenol was elevated in microsomes from animals that had received acetone (1%) in their drinking water for 1 week to 230% and 200%, respectively, of control values in mouse microsomes and to 310% and 240%, respectively, of control values in rat microsomes. Pretreatment of animals with 4-methylpyrazole (200 mg/kg intraperitoneally, once daily for 3 days) increased metabolism of N-methylformamide to 410% of control values in rat liver microsomes but was without effect on murine microsomal metabolism of N-methylformamide. The metabolism of this compound was strongly inhibited by the CYP2E1 substrates or inhibitors dimethylsulfoxide (1-100 mM), p-nitrophenol (100 microM), and diethyldithiocarbamate (100 microM), which did not affect aminopyrine N-demethylation. A polyclonal antibody against rat CYP2E1 (10 mg of IgG/nmol of cytochrome P450) inhibited N-methylformamide metabolism in liver microsomes from rats and from a human by 75% and 80%, respectively. The rate of metabolism of N-methylformamide to S-(N-methylcarbamoyl) glutathione was determined in liver microsomes from six humans and correlated with extent of metabolic hydroxylation of chlorzoxazone, a CYP2E1 probe, and with amount of immunodetectable enzyme using an anti-rat CYP2E1 antibody (r = 0.81 and 0.80, respectively). The results suggest that CYP2E1 is the predominant, if not sole, cytochrome P450 isozyme responsible for the metabolic toxification of hepatotoxic N-alkylformamides.

Acetone↗
PubMed1992

The long-term effects of aerosol pentamidine on pulmonary function. The Toronto Aerosolized Pentamidine Study (TAPS) Group.

Aerosolized pentamidine (AP) has been widely used for prophylaxis of pneumocystis carinii pneumonia (PCP) since 1988. The objective of this study was to evaluate the long-term effects of AP on pulmonary function. Of 36 patients with AIDS who were receiving AP for secondary prophylaxis of PCP, 13 patients had been using AP continuously for more than 52 weeks. AP was given using a Fisoneb ultrasonic nebulizer with five loading doses of 60 mg over two weeks, followed by one dose of 60 mg every two weeks. Baseline PFT were TLC 92 +/- 14% pred, FVC 90 +/- 11% pred, FEV1 91 +/- 11% pred, FEF25-75 95 +/- 17% pred, and DLCO (corrected for hemoglobin) 70 +/- 22% pred. No significant change in TLC, FVC, FEV1, or DLCO was seen after 56 weeks of AP. There was a 20% fall in FEF25-75 seen after 56 weeks, which was statistically significant. However, the clinical significance of a fall of this magnitude in the FEF25-75 is uncertain. Similar results were seen in a smaller subset of patients who received AP for at least 76 weeks. Although the small sample size must be considered, this data suggests that there is no clinically significant change in pulmonary function associated with the use of AP for up to 76 weeks.

Acquired Immunodeficiency Syndrome↗
PubMed1991

Positive end-expiratory pressure vs T-piece. Extubation after mechanical ventilation.

Because T-piece breathing may impair oxygenation, the best airway pressure from which to extubate ventilated patients is controversial. We compared the effects of extubation after 1 h of either CPAP 5 and T-piece/ZEEP. Once weaned from mechanical ventilation and breathing spontaneously, 106 patients were randomized to 1 h CPAP or 1 h T-piece/ZEEP, following which patients were extubated and mask O2 administered. No significant difference existed between groups in age, sex, HR, BP, FIO2, PaCO2 or PaO2. However, P(A-a)O2 was significantly greater at 120 min in the CPAP group. Within the CPAP group, P(A-a)O2 was also significantly worse at 120 vs 0 min. Nineteen T-piece patients showed improved P(A-a)O2 at 120 min compared with only ten CPAP patients. Three CPAP and two T-piece patients subsequently required reintubation. This study demonstrates that use of a T-piece dose not impair arterial oxygenation and may in fact be superior to direct extubation from CPAP 5.

Humans↗
PubMed1991

Pneumothorax resulting from acupuncture.

The authors report two cases of pneumothorax secondary to lung puncture, which was caused by acupuncture needles. Radiologists should be alert to this possible cause of pneumothorax, particularly when needle fragments can be seen in radiographs of the soft tissues.

Acupuncture Analgesia↗
PubMed1990

Legionella lung cavitation.

Pneumonia due to Legionella has been identified in a small percentage of patients suffering from acquired immune deficiency syndrome (AIDS), with and without coexisting Pneumocystis carinii pneumonia. On chest radiographs Legionella typically produces focal parenchymal opacities and confluent lobar consolidation. The authors describe a case of cavitating Legionella pneumonia, which occurred in a 38-year-old man who had AIDS. The main differential diagnoses are an unusual presentation of P. carinii pneumonia and fungal infection. The authors also emphasize the increasing recognition of bacterial pneumonia with atypical radiologic features in AIDS patients.

Acquired Immunodeficiency Syndrome↗
PubMed1985

Longitudinal study of grain elevator and control workers with demonstration of healthy worker effect.

Changes in the respiratory symptoms and pulmonary function of 441 grain elevator workers and a control group of 180 civic workers during a three-year period were compared. The grain handlers who left their jobs during the interval between the first and second surveys were found to have shown a significantly higher prevalence of cough and shortness of breath at the beginning of the study period than those who remained employed; this difference was not observed among the civic workers. The grain and civic workers who were examined on both occasions showed similar longitudinal changes in their symptoms and pulmonary function. Nevertheless, the results of this study are biased by the healthy worker effect among the grain handlers.

Age Factors↗