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S Naylor

Publications and source records attributed to S Naylor.

At least 109 records · Page 6Linked to original sources
PubMed1995

Characterization of 2-amino-1-benzylbenzimidazole and its metabolites using tandem mass spectrometry.

We have investigated the in vitro hamster hepatic microsomal metabolism of the amino-azaheterocycle, 2-amino-1-benzylbenzimidazole (ABB). Three major metabolites were isolated and structurally characterized, using a combination of off-line HPLC, in conjunction with both electron ionization and fast atom bombardment ionization tandem mass spectrometry. ABB was shown to be debenzylated to afford 2-aminobenzimidazole (AB), as well as N- and C-oxidized to give 1-benzyl-N2-hydroxyaminobenzimidazole (BHB) and 2-amino-1-benzyl-hydroxybenzimidazole, respectively. The possible reasons for formation of the exocyclic hydroxylamine BHB are discussed. Furthermore, ABB is proposed as a suitable model compound for investigating parameters that control formation of toxic hydroxylamines derived from amino-azaheterocycles.

Animals↗
PubMed1995

Microcell mediated chromosome transfer maps the Fanconi anaemia group D gene to chromosome 3p.

Fanconi anaemia (FA) is an autosomal recessive disorder characterized by progressive pancytopenia, short stature, radial ray defects, skin hyperpigmentation and a predisposition to cancer. Cells from FA patients are hypersensitive to cell killing and chromosome breakage induced by DNA cross-linking agents such as mitomycin C (MMC) and diepoxybutane (DEB). Consequently, the defect in FA is thought to be in DNA crosslink repair. Additional cellular phenotypes of FA include oxygen sensitivity, poor cell growth and a G2 cell cycle delay. At least 5 complementation groups for Fanconi anaemia exist, termed A through E. One of the five FA genes, FA(C), has been identified by cDNA complementation, but no other FA genes have been mapped or cloned until now. The strategy of cDNA complementation, which was successful for identifying the FA(C) gene has not yet been successful for cloning additional FA genes. The alternative approach of linkage analysis, followed by positional cloning, is hindered in FA by genetic heterogeneity and the lack of a simple assay for determining complementation groups. In contrast to genetic linkage studies, microcell mediated chromosome transfer utilizes functional complementation to identify the disease bearing chromosome. Here we report the successful use of this technique to map the gene for the rare FA complementation group D (FA(D)).

Cell Line↗
PubMed1994

Photolysis of sulfiram: a mechanism for its disulfiram-like reaction.

Sulfiram, a drug applied topically to treat scabies, produces effects similar to those of disulfiram after subsequent ingestion of ethanol. Disulfiram, used in aversion therapy in the treatment of alcoholism, inhibits hepatic aldehyde dehydrogenase (ALDH) causing an accumulation of acetaldehyde after ethanol ingestion. The increased tissue levels of acetaldehyde cause a spectrum of undesirable side-effects including flushing, nausea, vomiting, and tachycardia, which are referred to as the disulfiram reaction. Previous studies have shown that in vitro sulfiram is a very weak inhibitor of ALDH, but solutions of sulfiram markedly increase in potency with time. In the present study, fresh solutions of sulfiram were exposed to fluorescent room light under ambient conditions and analyzed at timed intervals by HPLC. At least eight products, including disulfiram, were formed in the light-exposed sulfiram solutions, but not in solutions kept in the dark. Structural characterization of two of the photolysis products was obtained by on-line microbore HPLC-mass spectrometry (mu LC-MS) and on-line microbore HPLC-tandem mass spectrometry (mu LC-MS/MS) using continuous flow-liquid secondary ion mass spectrometry (CF-LSIMS) as the primary ionization method. Sulfiram was converted to disulfiram at an initial rate of 0.7%/hr, and the formation of disulfiram correlated with the increase in ALDH inhibition in vitro. The results of this investigation show that while sulfiram is a weak inhibitor of ALDH in vitro, it is readily photoconverted to disulfiram, a very potent inhibitor of ALDH, which may explain the adverse reaction to ethanol after sulfiram therapy.

Aldehyde Dehydrogenase↗
PubMed1994

Investigation of the in vitro metabolism of the H2-antagonist mifentidine by on-line capillary electrophoresis-mass spectrometry using non-aqueous separation conditions.

The in vitro metabolism of mifentidine, a prototype second-generation histamine H2-antagonist, is investigated using on-line capillary electrophoresis-mass spectrometry (CE-MS) by analysis of hepatic microsomal incubates. Consideration of the hydrophobicity of this drug and putative metabolites led to the development of a non-aqueous CE separation medium consisting of 5 mM NH4OAc in methanol containing 100 mM acetic acid. Benefits of non-aqueous media in CE-MS studies of small hydrophobic molecules are discussed. In addition, we elucidate both chemical transformations and the in vitro metabolism of mifentidine using guinea pig hepatic microsomes.

Animals↗
PubMed1994

Investigation of drug metabolism using capillary electrophoresis with photodiode array detection and online mass spectrometry equipped with an array detector.

The application of capillary electrophoresis (CE) with photodiode array detection (DAD) and on-line CE-mass spectrometry (CE-MS) equipped with a position and time resolved (PATRIC) focal plane detector for analysis of both in vitro and in vivo drug metabolism is demonstrated. Separation of metabolites derived from the neuroleptic drug haloperidol, by CE, using a simple, volatile run buffer containing 50 mM ammonium acetate with 10% methanol and 1% acetic acid is reported. The potential utility of CE-DAD for screening drug metabolite mixtures derived from hepatic microsomal incubations is demonstrated for haloperidol (HAL). Also the potential problems associated with using this technology to screen human urine samples for HAL metabolites is discussed. Furthermore, the usefulness of CE-MS and CE-electrospray ionization skimmer collision induced dissociation-MS (CE-ESI-CID-MS) in identification and structure elucidation of HAL metabolites derived from both a guinea pig hepatic microsomal incubation and urine from a patient treated with 0.5 mg/day of HAL is shown. The utility of such an approach in the general area of clinical pharmacology is also discussed.

Animals↗
PubMed1994

The highly efficient production of full-length and mutant rat brain calcium-binding proteins (calbindins-D28K) in a bacterial expression system.

We expressed gram amounts of full-length and mutant rat brain calcium-binding proteins (calbindins-D28K) lacking one or two "EF-hand" motifs in a bacterial expression system. The cDNA for the full-length rat calcium-binding protein was cloned into the NdeI and BamHI sites of the pET3a vector. Additionally, constructs of the rat brain calcium-binding protein lacking EF-hand 2 (delta 2 mutant), EF-hand 6 (delta 6 mutant), and EF-hands 2 and 6 (delta 2, 6 mutant) were constructed using the same vector. These chimeric plasmids were used to transfect BL21 (DE3) pLysS Escherichia coli cells. Following transformation, the cells were grown in the presence of isopropylthiogalactoside in order to induce bacterial T7 polymerase, which resulted in the production of large amounts of the proteins of interest in the bacterial cytosol. Expressed full-length and delta 2 and delta 2,6 mutant proteins represented 50% or more of total bacterial protein. The delta 6 protein was not expressed. Cell lysis followed by purification of the proteins on DEAE-cellulose routinely resulted in gram yields of the proteins. The purified proteins displayed the appropriate amino acid composition and amino-terminal amino acid sequence. When analyzed by matrix-assisted laser desorption mass spectrometry the proteins were found to have the appropriate molecular weights (within the accuracy limits of the instrument). The expressed proteins bound to a polyclonal antiserum raised against chick intestinal calcium-binding protein. In addition, the full-length, delta 2, and delta 2,6 mutants bound calcium as assessed by a 45Ca blotting procedure. The production of large amounts of readily purified vitamin D-dependent calcium-binding proteins should be useful in biophysical studies of the proteins.

Amino Acid Sequence↗
PubMed1994

Chromosomal localization of the parathyroid hormone/parathyroid hormone-related protein receptor gene to human chromosome 3p21.1-p24.2.

The human PTH/PTH-related peptide (PTH/PTHrP) receptor could be involved in hereditary disorders of PTH or PTHrP action. Knowledge of the gene's chromosomal location would allow studies linking it to specific disease traits. Therefore, we mapped the human PTH/PTHrP receptor gene by polymerase chain reaction of human/rodent somatic cell hybrid panels using oligonucleotide primers designed to amplify a portion of the gene from genomic DNA. The PTH/PTHrP gene was unambiguously assigned to the short arm of human chromosome 3, in the region designated 3p21.1-p24.2. Analysis of a second chromosome 3-specific mapping panel suggests that the gene is located near the 3p21.2-p21.3 boundary. The availability of highly polymorphic markers located in this region will permit exploration of the PTH/PTHrP receptor locus in genetic linkage searches for the causes of bone, calcium, and other potential disorders.

Animals↗
PubMed1993

Investigation of the metabolic fate of the neuroleptic drug haloperidol by capillary electrophoresis-electrospray ionization mass spectrometry.

Combined capillary electrophoresis-mass spectrometry (CE-MS) is a powerful analytical tool for the characterization of components of complex mixtures. Furthermore, when interfaced with an electrospray ionization (ESI) source, skimmer induced fragmentation can yield structural information that aids compound identification. We show that these techniques can be used to probe the metabolic fate of drugs by investigation of the phase I metabolism of the widely used neuroleptic drug haloperidol. In addition, we demonstrate differences of in vitro metabolism of haloperidol by mouse and guinea pig hepatic microsomes.

Animals↗
PubMed1993

Investigation of the metabolism of the neuroleptic drug haloperidol by capillary electrophoresis.

Free solution capillary electrophoresis (FSCE) conditions were previously reported to be of limited use for the separation of pharmaceuticals, since many of these compounds are neutral. We show that by consideration of compound hydrophobicity and ionisable functional groups, FSCE conditions can be developed to effect the separation of a drug and its phase I metabolites. This is brought about by adding a suitable organic modifier to aid solubility, and modifying pH to effect a change in the mass to charge ratio of the metabolites present. Furthermore, we show that in this drug metabolism study, FSCE presents an advantage over both reversed-phase HPLC and micellar electrokinetic chromatography. We also demonstrate the use of FSCE for investigation of the phase I metabolites produced by the in vitro incubation of haloperidol (a neuroleptic agent) with both mouse and guinea pig hepatic microsomes and show that such an approach can be used to detect both qualitative and quantitative differences in species metabolism.

Animals↗
PubMed1993

An evaluation of tandem mass spectrometry in drug metabolism studies.

The use of precursor ion and constant neutral loss scanning as a means of rapidly detecting drug metabolites is evaluated. Four clinically useful drugs, namely (i) cyclophosphamide, (ii) mifentidine, (iii) cimetropium bromide and (iv) haloperidol, were subjected to microsomal incubations to afford phase I metabolites. Aside from a minor clean-up procedure involving zinc sulfate precipitation of microsomal proteins and solid-phase extraction of metabolites using a Sep-pak C-18 cartridge, the mixtures were analysed directly by fast atom bombardment tandem mass spectrometry. It is demonstrated that such screening strategies are important in detecting novel metabolites. However, there are some problems associated with only using such methods, including (i) the possibility of not detecting metabolites that undergo unusual collision-induced dissociation fragmentation pathways, (ii) the non-detection of metabolites that have undergone metabolic change at unusual sites of reactivity, and (iii) production of artifacts derived from the parent drug by the primary ionization process. Examples are discussed that highlight both the strengths and weaknesses of such an approach.

Cyclophosphamide↗
PubMed1993

Identification of endogenous electrophiles by means of mass spectrometric determination of protein and DNA adducts.

Monitoring exposure to alkylating agents may be achieved by quantitatively determining the adduct levels formed with nucleic acids and/or proteins. One of the most significant results arising from the application of this approach has been the discovery in control populations of "background" levels of alkylated nucleic acid bases or alkylated proteins, in particular hemoglobin (Hb). In the case of Hb, a wide variety of such adducts have been detected and quantitated by mass spectrometric techniques, with methylated, 2-carboxyethylated, and 2-hydroxyethylated modifications being most abundant. Although the source of these alkylation products is unknown, both endogenous and exogenous sources may be proposed. We have recently confirmed the presence of the N-terminal hydroxyethylvaline adduct in control human Hb using tandem mass spectrometry (MS-MS) and have now established background levels using GC-MS in more than 70 samples. Smoking raises the levels of the adduct up to 10-fold and occupational exposure to ethylene oxide up to 300-fold. Background levels of alkylated nucleic acids may be studied by analysis of N7-alkylated guanine or N3-alkylated adenine, which are excised from nucleic acids after their formation and are excreted in urine. Although the presence of some of these urinary constituents may be accounted for by their natural occurrence in RNA or diet, the endogenous or exogenous source of others is unknown. Quantitative methods using MS-MS have now been developed for five of the observed urinary alkylguanines [N7-methyl-, N2-methyl-, N2-dimethyl-, N7-(2-hydroxyethyl)-, and N2-ethylguanine].(ABSTRACT TRUNCATED AT 250 WORDS)

Alkylating Agents↗
PubMed1992

Identification of metabolites of 4,4'-diaminodiphenylmethane (methylene dianiline) using liquid chromatographic and mass spectrometric techniques.

The in vitro metabolism of 4,4'-diaminodiphenylmethane (methylene dianiline, MDA) was investigated using rabbit liver microsomes. Minimal clean-up of the microsomal incubations was carried out using zinc sulphate precipitation followed by solid-phase extraction on Sep-Pak C18 cartridges. Three metabolites were detected in hepatic microsomal incubations, namely the azodiphenylmethane (azo) azoxydiphenylmethane (azoxy) and 4-nitroso-4'-aminodiphenylmethane (nitroso) compounds. The azo and azoxy metabolites were produced enzymatically whereas the nitroso compound may have been formed via a non-enzymatic process. Reversed-phase high-performance liquid chromatography-plasma spray mass spectrometry was used to initially detect these metabolites. Fast atom bombardment mass spectrometry and fast atom bombardment tandem mass spectrometry were utilized to further structurally characterise these compounds. Comparison of mass spectral data obtained from synthesised standards with data obtained on the putative metabolites substantiated the characterisation of these compounds.

Aniline Compounds↗
PubMed1992

Rapid and efficient purification of cimetropium bromide and mifentidine drug metabolite mixtures derived from microsomal incubates for analysis by mass spectrometry.

A comparative study of the use of organic solvent extraction versus Sep-Pak C18 cartridges in the recovery and analysis of phase I (unconjugated) drug metabolites using mass spectrometry is presented. Standard mixtures of putative metabolites of the anticholinergic drug cimetropium bromide and the H2-antagonist mifentidine were purified from inactivated liver microsomal preparations using both methods, and subsequently the recovery of each compound was quantitated. In general, the percentage recovery and degree of purification were greater when using Sep-Pak C18 cartridges compared with organic solvent extraction. Even more efficient recovery was achieved when zinc sulphate precipitation of proteins in the liver microsomal mixtures was carried out prior to analysis. Also, the HPLC-grade solvents used in this study contained a variety of ultraviolet-inactive, hydrophobic components. This leads to problems of suppression in fast atom bombardment mass spectrometric analysis. Using Sep-Pak C18 cartridges directly prior to analysis by fast atom bombardment with single or tandem mass spectrometry leads to far superior mass spectral results compared with organic solvent extraction.

Androgen Antagonists↗
PubMed1992

Bioanalytical applications of tandem mass spectrometry in the in vitro metabolism of the anticholinergic drug cimetropium bromide to detect differences in species metabolism.

1. In vitro metabolism of the anticholinergic drug, cimetropium bromide, was investigated using four different animal hepatic microsomal incubates derived from rat, hamster, guinea pig, and mouse livers. 2. Constant neutral loss (CNL) tandem mass spectrometry was used to detect the presence of the N-methylenecyclopropyl-scopine functionality by monitoring loss of 54 daltons (corresponding to loss of methylenecyclopropane) in microsomal incubates. 3. A CNL loss of 46 daltons was used to screen for the presence of ester hydrolysis products. 4. A comparison of the daughter ion spectra obtained on ions detected by CNL scanning, with daughter ion spectra of synthetic standards, determined the presence of ten metabolites of cimetropium bromide. 5. Hydroxylation of the aromatic ring in the ester side-chain was found to be the major metabolic pathway, and ester bond hydrolysis was a minor metabolic pathway. 6. N-Demethylation of the bridgehead nitrogen was observed only in rat and hamster incubates. 7. Using the method of CNL scanning it was possible to screen different animal microsomal incubates without resorting to any major purification procedures such as h.p.l.c. 8. This scanning method revealed differences between species in the metabolic pathways of cimetropium bromide.

Animals↗
PubMed1991

Isolation of two N-monosubstituted protoporphyrins, bearing either the whole drug or a methyl group on the pyrrole nitrogen atom, from liver of mice given griseofulvin.

1. A hepatic green pigment with inhibitory properties towards the enzyme ferrochelatase has been isolated from the liver of mice treated with griseofulvin and identified as N-methylprotoporphyrin. 2. All four structural isomers of N-methylprotoporphyrin have been demonstrated to be present, NA, where ring A of protoporphyrin IX is N-methylated, being the predominant isomer. 3. In addition to N-methylprotoporphyrin, a second green pigment, present in far greater amounts, was also isolated from the liver of griseofulvin-treated mice. This second green pigment is also an N-monosubstituted protoporphyrin, but in this case the substituent on the pyrrole nitrogen atom appears to be intact griseofulvin rather than a methyl group. 4. The fragmentation of this adduct in tandem m.s. studies suggests that griseofulvin is bound to the pyrrole nitrogen through one of its carbon atoms and further suggests that N-methylprotoporphyrin may arise as a secondary product from the major griseofulvin pigment.

Animals↗
PubMed1991

Gas chromatographic-mass spectrometric analysis of diols and tetrols from reactions of polycyclic aromatic hydrocarbon epoxides with hemoglobin.

We have evaluated both electron ionization (EI) and negative-ion chemical ionization (NICI) methods for the analysis of trimethylsilyl derivatives of a series of polycyclic aromatic hydrocarbon (PAH) alcohols including styrene diol, benzo[e]pyrene diol and tetrols, cyclopenta[c,d]pyrene diols, benzo[a]pyrene-4,5-diols, chrysene tetrols, benz[a]anthracene tetrols I and II, and syn- and anti-benzo[a]pyrene tetrols. NICI is the more sensitive method for all compounds except styrene diol. Detection limits are compound-dependent and range from 1 fmol for cyclopenta[c,d]pyrene diol to 1 pmol for benzo[e]pyrene diol. The EI detection limit for styrene diol is 60 fmol. PAH alcohols related to the compounds listed above were observed following hydrolysis of hemoglobin which had been reacted with PAH epoxides in vitro. Benzo[a]pyrene tetrols and a chrysene tetrol were observed following hydrolysis of hemoglobin isolated from human smokers' blood. Hydrolysis of styrene oxide treated hemoglobin in 18O-labeled water revealed at least two mechanisms of ester hydrolysis, including the BAL 1 pathway.

Alcohols↗