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M V Doig

Publications and source records attributed to M V Doig.

6 recordsLinked to original sources
PubMed1991

Use of thermospray liquid chromatography-mass spectrometry to aid in the identification of urinary metabolites of a novel antiepileptic drug, Lamotrigine.

The use of thermospray liquid chromatography-mass spectrometry allowed the structural elucidation of a number of urinary metabolites of Lamotrigine, 3,5-diamino-6-(2,3-dichlorophenyl)-1,2,4-triazine, formed after administering the drug to man, Cynomolgus monkey and rabbit. This data when combined with the data obtained from high-performance liquid chromatography with radiochemical detection enabled us to determine the types and amounts of unchanged drug and metabolites excreted in urine by man and a number of laboratory animal species. This technique was particularly useful as it highlighted a previously unknown fact that Lamotrigine is metabolised to form two different N-glucuronides, one of which is resistant to cleavage in vitro by a crude beta-glucuronidase preparation from Helix pomatia.

Animals↗
PubMed1991

Gas chromatographic-mass spectrometric characterisation of some novel hydroxyeicosatetraenoic acids formed on incubation of arachidonic acid with microsomes from induced rat livers.

The biotransformation of arachidonic acid by rat liver microsomes from both control animals and animals pretreated with known inducers of cytochrome P-450 isoenzymes has been studied using a combination of reversed- and normal-phase high-performance liquid chromatography and combined gas chromatography-electron-impact mass spectrometry. The metabolite profiles observed were found to be dependent upon the inducing agent. Five metabolites were identified, namely 16-, 17-, 18-, 19- and 20-hydroxylated arachidonic acids. Of these the 16- and 17-isomers have not been reported as products of arachidonic acid metabolism by any biological system and the 18-isomer has not been reported as a product of liver metabolism.

Animals↗
PubMed1990

Method validation in the bioanalytical laboratory.

Bioanalytical methods, based on a variety of physico-chemical and biological techniques such as chromatography, immunoassay and mass spectrometry, must be validated prior to and during use to engender confidence in the results generated. The fundamental criteria for assessing the reliability and overall performance of a bioanalytical method are: the evaluation of drug and analyte stability, selectivity, limits of quantification and detection, accuracy, precision, linearity and recovery. The extent to which a method is validated is dependent on its prospective use, the number of samples to be assayed and the use to which the data are put. Specific analytical techniques may require additional validation such as antibody-binding characteristics, peak purity determination, evaluation of matrix effects or structural confirmation of the analyte. Ideally each assay should be cross-validated with a method utilizing a highly specific detector such as a mass spectrometer. Once in use, the performance of the method should be monitored using quality control standards. If a method is set up in another laboratory, the performance of that assay should be monitored with quality control standards sent from the originating laboratory.

Chemistry, Pharmaceutical↗
PubMed1989

Role of hepatic and renal cytochrome P-450 IVA1 in the metabolism of lipid substrates.

The role of clofibrate-inducible cytochrome P-450 IVA1 in the metabolism of endogenous lipids in both rat liver and kidney microsomal fractions has been investigated. 20(omega)-hydroxyarachidonic acid has been identified as a major metabolite after incubation with both tissue fractions and the structure confirmed by mass spectrometry. The arachidonic acid 20-hydroxylase activity is inducible by clofibrate in both liver and kidney, indicating that cytochrome P-450 IVA1 is probably the enzyme responsible for this activity. In addition, the kidney exhibited higher rates of arachidonate 20-hydroxylase activity than the liver (in both control and induced states). Although leukotriene B4 was also hydroxylated in the 20-position in both liver and kidney, clofibrate induction resulted in a decrease (approximately 50%) in hydroxylase activity. In addition, the absolute level of leukotriene B4 20-hydroxylase activity in both tissue homogenates and by purified cytochrome P-450 IVA1 in a reconstituted system, was 2-3 orders of magnitude lower than the corresponding activity for lauric acid and arachidonic acid as substrates, indicating that the leukotriene was not the preferred substrate for this enzyme. Computer modelling of the conformational geometries of the above three potential cytochrome P-450 IVA1 substrates have shown that both lauric and arachidonic acids adopt a compact, 'hairpin' structure that are almost superimposed on each other, thereby rationalizing why they are relatively good substrates for this isoenzyme. By contrast, leukotriene B4 adopts a more bulky geometry than the two fatty acids, thereby providing a coherent structural reason why it is a poorer substrate for the cytochrome P-450 IVA1 isoenzyme.

Animals↗