PubMed Health⌕ Search

Biomedical subjects

J W Gorrod

Publications and source records attributed to J W Gorrod.

At least 19 recordsLinked to original sources
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

Microsomal formation of N-benzyl-4-hydroxymethylaniline from N-benzyl-4-methylaniline.

The in-vitro metabolism of N-benzyl-4-methylaniline was re-examined using male hamster and rabbit hepatic microsomes; both species generated N-benzyl-4-hydroxymethylaniline, confirmed by TLC and HPLC, comparison with authentic compound. Further confirmation of the formation of this metabolite was achieved by use of a rapid scan UV detector.

Animals↗
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

Dehydration is the first step in the bioactivation of haloperidol to its pyridinium metabolite.

Haloperidol was found to have a similar metabolic pathway to that of the neurotoxin N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in mice microsomal preparations. The 1,2,3,6-tetrahydropyridine derivative of haloperidol was detected in NADPH-fortified metabolic incubation mixtures of haloperidol. Incubation of this dehydrated haloperidol produced the pyridinium metabolite. These metabolites were confirmed by comparison with synthesised compounds using HPLC and HPLC-MS. Dehydration of an alcohol to a double bond represents a novel metabolic pathway. This novel metabolic pathway indicates a MPTP-like mechanism for the Parkinsonism observed with haloperidol in clinical use.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1989

Pyrolysis gas-liquid chromatography of N,N-dimethylalkylamine N-oxides and their mixtures.

A rapid quantitative and small scale method based on direct injection pyrolysis gas-liquid chromatography is described for the determination of N,N-dimethylalkylamine N-oxides. The method is suitable for determination of individual N-oxides as well as of their homologous compositions with or without the presence of parent tertiary amines in water or methanol solutions. The sensitivity of the method is 10-15 nmol of compounds injected. The unsymmetrical (1-methyldodecyl)dimethylamine N-oxide forms two isomeric alkenes 1-tridecene and trans-2-tridecene in a ratio of 1.68, in agreement with the predicted value.

Chromatography, Gas↗
PubMed1989

A rationale for the non-mutagenicity of 2- and 3-aminobiphenyls.

Of the three isomeric forms of aminobiphenyl, only 4-aminobiphenyl is an established carcinogen while the 2-isomer is considered as a non-carcinogen and 3-aminobiphenyl is at best described as a weak carcinogen. In the present studies we investigated the mutagenicity of these three compounds, their N-hydroxy derivatives and their nitrosoderivatives in the Ames test using the Salmonella typhimurium strains TA98 and TA100. The studies were performed both in the absence and presence of an activation system derived from the liver of rats pretreated with Aroclor 1254. Of the three isomers only 4-aminobiphenyl exhibited mutagenicity and only in the presence of an activation system. N-Hydroxy-4-aminobiphenyl was a potent direct mutagen in both bacterial strains, N-hydroxy-2-aminobiphenyl was mutagenic in only TA100 while N-hydroxy-3-aminobiphenyl displayed mutagenicity in neither strain. Both 2- and 3-nitrosobiphenyls were direct mutagens in strain TA100. These findings suggest that the weak carcinogenicity of 3-aminobiphenyl may be attributed to the lack of genotoxicity of its N-hydroxyderivative, whereas in the case of 2-aminobiphenyl it may be due to the inability of the hepatic preparations to catalyse its N-hydroxylation, which is in agreement with published in vivo metabolic studies. It is interesting that of the three isomers only 2-aminobiphenyl is non-planar, forming a dihedral angle of 40 degrees, and this may preclude it from acting as a substrate of the P-450I family of haemoproteins, which selectively catalyses the N-hydroxylation of many aromatic amines including 4-aminobiphenyl.

Aminobiphenyl Compounds↗
PubMed1989

QSAR study on species differences in microsomal N-oxygenation of N,N-dimethylalkylamines.

The metabolic N-oxygenation of nine long chain N,N-dimethylalkylamines and tri-n-butylamine has been studied using hepatic microsomal homogenates from mice, dogs and guinea-pigs. The relative oxidizability of amines (ROA) was correlated with structure, lipophilicity and nucleophilicity parameters of substrates and corresponding amine oxides formed in this biological reaction. The highest conversion of amines to N-oxides was found with male guinea-pig, followed by dog (male, female) and the lowest amount of amine oxides has been produced with male mice microsomal homogenates. The analyses were carried out by GLC and the results quantified using QSAR methodology. ROA is parabolically dependent upon structure and physicochemical properties of the substrates and products which was proved by the high statistical significance of the regression equations. The biological N-oxygenation of these amines is controlled by lipophilicity, stereochemistry and electronic effects.

Animals↗
PubMed1989

Conformational analysis of 9-substituted adenines in relation to their microsomal N1-oxidation.

Metabolic N-oxidation of adenine, 9-methyladenine, 9-benzyladenine, 9-benzhydryladenine and 9-trityladenine has been investigated using hepatic microsomes from hamster, guinea-pig, rabbit, mouse, rat, and dog. N1-Oxide formation occurs with 9-benzyladenine and 9-benzhydryladenine using liver preparations of all species examined, although to different extents. The N-oxidase activity was found, amongst rodents, in the order hamster greater than mouse greater than rabbit greater than rat greater than guinea-pig. Microsomal preparations from dog liver contained a small quantity of P-450 and yet produced a relatively large amount of the N-oxides, possibly indicating that other cytochromes in addition to P-450 may be involved in the N-oxidation of these compounds. The most favourable conformations of these 9-substituted analogues have been established using computer graphics modelling and 1H NMR techniques. Results obtained confirmed the importance of the stereochemical properties of these compounds in relation to N1-oxidation. These observations substantiate and extend our previous findings on the electronic, lipophilic, and stereochemical factors affecting the N-oxidation of adenine derivatives.

Adenine↗
PubMed1989

In vitro metabolic N-oxidation of azo compounds. I. Evidence for formation of azo N-oxides (azoxy compounds).

Certain azo compounds and their N-oxides have been prepared and characterized by spectroscopic methods. A HPLC method for the quantification of azo-N-oxide metabolites of those azo compounds is described. The enzymic N-oxidation of azo compounds in vitro has been demonstrated as a general metabolic pathway. In the case of the mixed aryl-alkyl azo compound, only one N-oxide was detected. The identity of N-oxide metabolites has been confirmed by CG/MS. Azo-N-oxidase activity was detected principally in the liver, but also in lung, heart and kidney whole organ homogenates. Studies using subcellular fractions showed that azo N-oxidase activity resides mainly in the hepatic microsomal fraction. The amount of N-oxide formed under optimised incubation conditions by hamster microsomal preparations is greatest with omega, omega'-azoxytoluene (AXT) and least with azoxybenzene (AXB); while omega-(phenylazoxy)toluene (PAXT) is intermediate.

Animals↗
PubMed1989

In vitro metabolic N-oxidation of azo compounds. II. Some factors influencing N-oxidation.

Factors affecting the metabolism of azo compounds in vitro have been studied and conditions which allow maximal metabolism established. A species difference in the extent of N-oxidation was evident, the order of activity depending on the class of substrate used. With the bisaryl azo compound, the order of activity was rabbit greater than hamster greater than mouse greater than guinea pig greater than rat, while for the bisalkyl and mixed alkyl-aryl azo compounds, the order was hamster greater than guinea pig greater than mouse greater than rabbit greater than rat. The appropriate kinetic factors, Km and Vmax, for the N-oxidation of azobenzene (AB), omega,omega'-azotoluene (AT) and omega-phenylazotoluene (PAT) are reported. A sex difference in azobenzene N-oxidase activity was observed in rats but not in hamsters.

Animals↗
PubMed1989

Biological N-oxidation of piperidine in vitro.

The biological N-oxidation of piperidine, a pharmacologically active biogenic amine of mammals and human beings, was studied in vitro. After incubation of piperidine-HCl in a fortified rat liver microsomal preparation (9000 x g supernatant) at 37 degrees C for 30 min, 2 metabolites were detected. They were identified as N-hydroxy piperidine and 2, 3, 4, 5-tetrahydro-pyridine-1-oxide as evidenced by TLC, GLC, HPLC, GC-MS and MS.

Animals↗
PubMed1987

The in vitro/in vivo comparative metabolism of 4-aminobiphenyl using isolated hepatocytes.

The metabolism of 4-aminobiphenyl by isolated hepatocytes from various species was compared with urinary metabolite profiles in the same species. Radioactive compounds in concentrates of ether extracts from hepatocytes or urine following hydrolysis were analysed by TLC and reversed phase HPLC in conjunction with radioactivity monitoring and synthetic standards. The major metabolites from hepatocytes and in urine were 4-acetamidobiphenyl, 3-hydroxy-4-aminobiphenyl 4'-hydroxy-4-aminobiphenyl and 4'-hydroxy-4-acetamidobiphenyl. Oxidation of the amine nitrogen gave hydroxylamino, nitroso and nitro compounds. Minor metabolites were 2'-hydroxy amine and amide, the hydroxamic acid and the oxamic acid. The urinary metabolite profiles correlated well with those from hepatocytes for each species.

Aminobiphenyl Compounds↗
PubMed1987

The oxidation of isomeric amino and acetamidobiphenyls by rat hepatic microsomal preparations.

The metabolism of isomeric amino and acetamidobiphenyls was studied using rat liver microsomal preparations. The aromatic amines were hydroxylated ortho or para to the amino group, whereas the aromatic amides were mainly oxidized in the para position. The carcinogenic amines 3- and 4- aminobiphenyl were converted to hydroxylamines and nitroso compounds. The non-carcinogenic amine 2-aminobiphenyl was resistant to enzymic nitrogen oxidation. The results support the concept that oxidation of aromatic amino groups is a prerequisite for carcinogenic and mutagenic activity.

Aminobiphenyl Compounds↗
PubMed1987

The in-vitro metabolism of [14C]pentobarbitone and [14C]phenobarbitone by hamster liver microsomes.

The metabolism of [14C]pentobarbitone and [14C]phenobarbitone has been reinvestigated using an in-vitro hepatic microsomal system (Syrian hamsters, Aroclor 1254 induction). The incubation system was routinely supplemented with EDTA (1 mM) and a substrate concentration study revealed the metabolism of [14C]pentobarbitone to be concentration-dependent, with the greatest overall metabolism (greater than 50%) occurring at 0.054 mumol per 3.5 mL. With [14C]phenobarbitone as substrate, overall metabolism was extremely low (3%) and independent of substrate concentration. Addition of further cofactors to the incubation mixture at 20 min intervals over an extended period resulted in almost complete metabolism of [14C]pentobarbitone (100 min), 3'-hydroxypentobarbitone and 3'-oxopentobarbitone being identified as metabolites together with many minor, unidentified products. With [14C]phenobarbitone as the substrate, cofactor addition up to 120 min resulted in 8% overall metabolism; p-hydroxyphenobarbitone was identified as a product of metabolism; other minor products were unidentified. The metabolism studies failed to produce a metabolite having the properties of the N-hydroxylated product of either [14C]pentobarbitone or [14C]phenobarbitone within the detection limits available (0.02% of 0.5 mumol per incubate).

Animals↗