Search PubMed⌕ Search

Biomedical subjects

A D Jones

Publications and source records attributed to A D Jones.

At least 91 records · Page 5Linked to original sources
PubMed1994

Stable isotope methods for the study of beta-carotene-d8 metabolism in humans utilizing tandem mass spectrometry and high-performance liquid chromatography.

This report presents analytical methods for the isolation and quantification of all-trans-beta-carotene-d8 in human plasma following a 73 mumol oral dose. Retinol-d4 derived from beta-carotene-d8 was also determined in the same plasma. Plasma samples drawn over a 24 day period were analyzed. beta-Carotene and retinol were isolated and purified for analysis using a solid phase extraction protocol with aminopropyl-bonded silica sorbent. Ratios of beta-carotene-d8/beta-carotene were determined using reversed-phase HPLC with spectrophotometric detection, which fully resolved the isotopomers, and by tandem mass spectrometry (MS/MS) with electron ionization. Results obtained from MS/MS and HPLC analysis showed close agreement and demonstrated improved selectivity relative to analysis using a single mass analyzer. Retinol-d4 was converted to its tert-butyldimethylsilyl ether and analyzed by gas chromatography/mass spectrometry using selected ion monitoring. The ability to resolve the beta-carotene isotopomers by HPLC makes it feasible for investigators without mass spectrometers to investigate the dynamics of absorption and metabolism of beta-carotene-d8 in humans.

Adjuvants, Immunologic↗
PubMed1994

Glutathione conjugation with the pyrrolizidine alkaloid, jacobine.

The reaction of glutathione with the epoxide containing pyrrolizidine alkaloid, jacobine, was catalyzed by guinea pig hepatic glutathione-S-transferase enzymes in in vitro experiments; the rate of the reaction in the presence of rat hepatic glutathione-S-transferases did not differ from the non-enzymatic rate. Using ion-pairing liquid chromatography we were able to isolate the conjugate and obtain a daughter ion spectrum using Fast Atom Bombardment Mass Spectrometry together with Collisionally Activated Dissociation/Mass Analyzed Kinetic Energy experiments.

Animals↗
PubMed1994

Maximum entropy deconvolution of heterogeneity in protein modification: protein adducts of 4-hydroxy-2-nonenal.

To explore the chemistry of the reactions of the cytotoxic aldehyde trans-4-hydroxy-2-nonenal (HNE) with proteins, we incubated this aldehyde in vitro with beta-lactoglobulin B, a model protein of molecular weight 18,277 Da. Direct characterization of reaction products using electrospray ionization mass spectrometry yielded spectra whose complexity suggested extensive product heterogeneity. Spectra were transformed to a true mass scale using both a conventional transform algorithm and a maximum entropy algorithm. Both transformations demonstrated the formation of aldehyde-protein adducts containing from three to nine aldehyde molecules per molecule of protein. Maximum entropy deconvolution resolved Schiff base adducts and/or dehydration products, differing from the Michael addition adducts by 18 Da. The dominant reaction pathway, however, was Michael addition of the aldehyde to nucleophilic functional groups on the protein. The large number of Michael adducts relative to the one available cysteine requires that other amino acids, such as histidine and lysine, also be modified. The data suggest that methods for analysis of HNE that involve displacement of Schiff base groups from proteins will only recover a small fraction of HNE.

Aldehydes↗
PubMed1994

Development of the Regular Interlaboratory Counting Exchanges (RICE) scheme to include visual reference counts and samples from asbestos clearance operations.

The RICE proficiency testing scheme for asbestos fibre counting operated until 1992 with industrial samples and with reference counts produced by an image analyser (Magiscan). The visual counts produced in RICE by the participating laboratories have now been used to develop a reliable reference count for these industrial samples. Concurrently with the routine participation in RICE, laboratories also counted samples from asbestos clearance operations; these counts were used to develop suitable reference counts and performance limits for this type of sample. The width of this satisfactory performance interval is proportional to the natural variation in the data on the samples and is therefore a fixed interval on the log scale (of sample density) for high density samples and a fixed interval on the square-root scale for low density samples (where counting normally stops after a fixed number of fields). These developments led to the introduction of visual reference counts and clearance samples into RICE during 1992.

Air↗
PubMed1994

Stable-isotope dilution GC-MS for determination of toluene in submilliliter volumes of whole blood.

An accurate and sensitive yet simple protocol for the analysis of toluene in submilliliter quantities of whole blood using stable-isotope dilution GC-MS has been developed and evaluated for use in pharmacokinetic studies of toluene exposure. The method involves the use of toluene-d8, a relatively inexpensive chemical used as a solvent for nuclear magnetic resonance spectroscopy, as an internal standard and extraction with pentane. This procedure allows for the determination of toluene in whole blood down to approximately 5 ng/mL and is suitable for pharmacokinetic measurements and biomonitoring of exposure to toluene.

Animals↗
PubMed1993

An improved protocol for determining ratios of retinol-d4 to retinol isolated from human plasma.

An improved protocol for assessing vitamin A status in humans using stable isotope dilution is described. Human subjects were given an oral dose of retinyl-d4 acetate, and blood specimens were collected after a period of pseudoequilibration. After the precipitation of proteins, the plasma was extracted with hexane and partitioned against acetonitrile. Retinol was isolated from the acetonitrile fraction using HPLC, and the retinol was converted to its tert-butyldimethylsilyl ether and analyzed by gas chromatography/mass spectrometry using selected-ion monitoring. The new method allows for more rapid isolation of retinol from plasma with fewer interferences than were seen in our earlier work. Significant improvements in the reliability, sensitivity, and precision of the method have been obtained in the present study, and these improvements should allow for the use of smaller doses of isotopically labeled vitamin A for evaluation of the vitamin A status of human populations.

Deuterium↗
PubMed1993

Hopanoid lipids compose the Frankia vesicle envelope, presumptive barrier of oxygen diffusion to nitrogenase.

Biological nitrogen fixation in aerobic organisms requires a mechanism for excluding oxygen from the site of nitrogenase activity. Oxygen exclusion in Frankia spp., members of an actinomycetal genus that forms nitrogen-fixing root-nodule symbioses in a wide range of woody Angiosperms, is accomplished within specialized structures termed vesicles, where nitrogen fixation is localized. The lipidic vesicle envelope is apparently a functional analogue of the cyanobacterial heterocyst envelope, forming an external gas-diffusion barrier around the nitrogen-fixing cells. We report here that purified vesicle envelopes consist primarily of two hopanoid lipids, rather than of glycolipids, as is the case in cyanobacteria. One envelope hopanoid, bacteriohopanetetrol phenylacetate monoester, is vesicle-specific. The Frankia vesicle envelope thus represents a layer specific to the locus of nitrogen fixation that is biosynthetically uniquely derived.

Journal Article↗
PubMed1993

Analysis of mercapturic acid conjugates of xenobiotic compounds using negative ionization and tandem mass spectrometry.

Mass spectra of mercapturic acid conjugates of two xenobiotic products of lipid peroxidation (trans-4-hydroxy-2-hexenal and trans-4-hydroxy-2-nonenal) as well as conjugates of 1,3-dichloropropene, styrene oxide, 1,2-naphthalene oxide and alpha-chlorotoluene were obtained using fast atom bombardment or negative chemical ionization. Fragmentation pathways were investigated using linked scan and mass-analyzed ion kinetic energy spectrometric techniques. Characteristics of the spectra obtained using different ionization and sample introduction techniques are compared. Deprotonated molecular ions of mercapturic acids gave simple daughter ion spectra, with the dominant mode of decomposition involving cleavage of C-S bonds giving a characteristic neutral loss of 129 Da. Screening for mercapturates in urine samples was performed using neutral loss scanning and yielded limits of detection in the low nanogram per milliliter range. Quantitative analysis of the S-benzyl mercapturic acid at 1 p.p.b. in urine has been demonstrated using combined gas chromatography/electron capture mass spectrometry with d3-S-benzyl mercapturic acid as internal standard.

Acetylcysteine↗
PubMed1993

COR pulmonale is caused by monocrotaline and dehydromonocrotaline, but not by glutathione or cysteine conjugates of dihydropyrrolizine.

Monocrotaline (MCT) produces pulmonary hypertension and right ventricular hypertrophy in rats. It is generally believed that MCT must undergo hepatic metabolism to reactive metabolites that are subsequently transported to the lungs to induce a pneumotoxic response. Several studies suggest that dehydromonocrotaline (MCTP) is the reactive intermediate that initiates pulmonary toxicity. We recently identified two other MCT metabolites, the glutathione and N-acetylcysteine conjugates of 6,7-dihydro-7-hydroxy-1-hydromethyl-5H-pyrrolizine (DHP). To determine the potential pulmonary toxicity of the glutathione conjugate (DHP-GSH) and the unacetylated cysteine conjugate precursor (DHP-Cys) of the N-acetylated excretion product, we conducted parallel in vivo toxicity studies with DHP-GSH, DHP-Cys, MCT, and MCTP. Relative pneumotoxicity was evaluated by measurements of right ventricular pressure (RVP), ventricular weight ratio (RV/LV+S), subjective histopathology, and measurements of components of the arteriolar wall. Animals given a single injection of MCT (60 mg/kg) developed pulmonary hypertension at the end of 3 weeks, as indicated by significant elevation in RVP when compared to the controls (22.1 +/- 2.4 mm Hg vs 13.2 +/- 0.8 mm Hg). A parallel and significant increase in RV/LV+S was also evident: 0.37 +/- 0.021 (MCT) vs 0.299 +/- 0.011 (control). Histopathology showed marked alterations in both pulmonary vasculature and parenchyma in MCT- and MCTP-treated animals. MCTP (1 mg/kg) caused a significantly elevated RVP (MCTP vs control: 28.1 +/- 3.4 mm Hg vs 16.8 +/- 0.97 mm Hg) and an increased RV/LV+S (MCTP vs control: 0.445 +/- 0.051 vs 0.284 +/- 0.026). Both MCT- and MCTP-treated rats had increased arteriolar medial thickness and decreased lumen diameter, but MCTP-treated rats had a milder vascular inflammatory response and less parenchymal lesions. Neither DHP-GSH (24 or 12 mg/kg) nor DHP-Cys (12 mg/kg) caused detectable changes in pulmonary circulation and no structural alteration in the lung was observed in these treatment groups. Although they are all pyrrolic metabolites of MCT, these studies demonstrate that only MCTP but not the glutathione or cysteine conjugates, is pneumotoxic at the doses tested.

Animals↗
PubMed1993

Respirable industrial fibres: deposition, clearance and dissolution in animal models.

This paper examines the available experimental and theoretical results describing deposition and clearance of mineral fibres inhaled by animals and humans in order to define the limits which these mechanisms impose on the relevance of animal experiments in the assessment of potential human health risks. Direct experimental data for deposition of spherical particles are extended by examination of the physical processes and by some limited experimental data for fibres. This shows that alveolar deposition efficiency (in rat and in man) is sufficiently similar for particles and fibres with aerodynamic diameters less that 5 microns for rats to be a relevant model for airborne dusts in this size range. Inter-species differences in mechanical clearance are substantial, with clearance being faster in the rat than in man, and this is a factor which should be considered in interpreting animal toxicity studies. The durability of fibres in the biochemical conditions of the lung may be more important over the longer lifespan of humans.

Air Pollutants, Occupational↗
PubMed1993

Solid-phase extraction protocol for isolating retinol-d4 and retinol from plasma for parallel processing for epidemiological studies.

Solid-phase extraction permits the parallel processing of samples in large numbers. We have applied this technique to the isolation of retinol isotopomers from plasma of humans participating in a study of vitamin A stable isotope dilution. The isotopomers were analyzed by gas chromatography/mass spectrometry. The extraction involves the separation of retinol from its aqueous matrix with a C18 silica-based sorbent followed by removal of lipid contaminants with an aminopropyl silica-based sorbent. Overall recovery of retinol from plasma was 47.2% +/- 1.8%. Purity of the retinol isolated from plasma is comparable with that obtained with a single HPLC method. This method permits the preparation of 32 samples per day by one analyst. Elimination of the need for HPLC permits sample preparation in the field with a minimum of equipment and technical skill.

Acetonitriles↗
PubMed1992

Formation of cyclic products from the diepoxide of long-chain fatty esters by cytosolic epoxide hydrolase.

Since diepoxides are known metabolites of polyunsaturated fatty acids, the action of the cytosolic epoxide hydrolase purified from liver tissue was examined on these diepoxides. Diepoxymethylstearate was metabolized to the corresponding tetraol by high concentrations of affinity-purified cytosolic epoxide hydrolase. When the enzyme was diluted (1000- to 2000-fold), disappearance of the tetraol metabolite occurred simultaneously with formation of other hydration products with GC retention times and chromatographic mobilities different from those of the tetraol. The hydration products were identified as tetrahydrofuran diols based on comparison of chromatographic properties and mass spectral information with the properties and spectra of chemically generated products. Also, a mixture of diepoxymethylarachidonates was hydrated to tetraols using concentrated enzyme. As the enzyme was diluted (1000- to 2000-fold), a decrease in tetraol formation occurred along with the elevation of other hydration products whose mass spectra were consistent with tetrahydrofuran diol structures. These data are consistent with the epoxide hydrolase at low concentrations acting to open one epoxide followed by nonenzymatic cyclization to the tetrahydrofuran diols. The data also suggest that oxygenated lipids may be endogenous substrates for the cytosolic epoxide hydrolase. Since some oxylipins are known chemical mediators, the in vivo presence and role of these novel diols and tetrahydrofuran diols should be examined.

Animals↗
PubMed1991

Biological activity of racemic folate mixtures fed to folate-depleted rats.

Most commercially available tretrahydro and substituted folates are racemic mixtures of R and S isomers about pteridine-carbon 6. Some reports show the unnatural stereoisomers modify specific aspects of folate metabolism, whereas others show no significantly different biologic effects between isomers. The extent to which unnatural folate stereoisomers are inert in vivo is unclear. Possible interactions between isomers at normal dietary folate intakes were tested by comparing growth, liver and serum folate concentrations, and congener patterns of folate-depleted rats fed amino acid-based diets with 283, 566 or 1132 nmol folic acid (standards), or 566 nmol racemic 5-methyltetrahydrofolate, 5-formyltetrahydrofolate or 5,10-diformyltetrahydrofolate/kg diet for 3 wk. Growth and tissue folate levels increased with each increment in dietary folic acid. Growth and liver and serum folate concentrations of rats fed 566 nmol 5-formyltetrahydrofolate or 5-methyltetrahydrofolate/kg diet were similar to those of rats fed 283 nmol folic acid/kg diet. Rats fed 5,10-diformyltetrahydrofolate lost weight and had depressed serum folate levels, and most died. Results show that biologic activity of racemic 5-formyltetrahydrofolate and 5-methyltetrahydrofolate was half that of folic acid, and the R isomer did not affect growth at the levels fed. Addition of a second formyl group destroyed folate bioactivity. The folate-depleted rat model is useful for testing biologic effects of individual folate stereoisomers in vivo as they become commercially available.

Administration, Oral↗
PubMed1991

Bacteriohopanetetrol: abundant lipid in frankia cells and in nitrogen-fixing nodule tissue.

An unusual class of lipid with amphiphilic properties has been detected in nodule tissue of Alnus and Ceanothus. High levels of the same lipid (20-50% of total cell lipids) were detected in solvent extracts of Frankia spp. cells. However, the lipid was absent in host roots. The lipid was purified and quantified by high-performance liquid chromatography/flame ionization detector. Phenol-sulfuric acid determinations and proton nuclear magnetic resonance indicated that the purified lipid is not a glycolipid. Mass spectra of the predominant species are consistent with published spectra for bacteriohopanetetrol (C(35)H(62)O(4)), a pentacyclic triterpenoid, or hopanoid.

Journal Article↗
PubMed1991

Experimental studies in rats on the effects of asbestos inhalation coupled with the inhalation of titanium dioxide or quartz.

Rats were exposed for 1 year, with a 2-year follow-up, to dust clouds consisting of a mixture of amosite or chrysotile asbestos with either titanium dioxide or quartz. The addition of titanium dioxide to asbestos did not increase levels of pulmonary fibrosis above the amounts produced by chrysotile or amosite alone. Quartz, however, greatly increased fibrosis above that produced by the asbestos types alone. Both particulate dusts caused an increase in the numbers of pulmonary tumours and mesotheliomas compared to asbestos alone but while tumours in animals treated with asbestos and quartz tended to occur earlier than tumours with asbestos alone, in animals treated with dusts containing titanium dioxide, tumour production occurred later than with asbestos alone. In animals treated with mixtures of asbestos and quartz, there was evidence of increased transport of fibres across the visceral pleural surface and this may be associated with the finding of a higher proportion of pleural mesotheliomas than previously reported in experimental inhalation studies from any laboratory using the main asbestos varieties. The presence of particulate dusts made little difference to the amounts of amosite fibre retained in the lung tissue but, with chrysotile, titanium dioxide appeared to increase retention while quartz reduced it.

Animals↗
PubMed1990

N-acetylcysteine-conjugated pyrrole identified in rat urine following administration of two pyrrolizidine alkaloids, monocrotaline and senecionine.

This report demonstrates that an Ehrlich-reagent-positive metabolite of monocrotaline and senecionine is excreted in the urine of male rats as an N-acetylcysteine conjugate of (+/-)-6,7-dihydro-7-hydroxy-1-hydroxymethyl-5H-pyrrolizine (NAC-DHP). Isolation of the metabolite employed an initial organic extraction followed by HPLC separation of remaining urinary components using a reverse-phase, polymer-based, PRP-1 column. Fast-atom-bombardment tandem mass spectrometry was used to identify the metabolite. This finding suggests that reactive metabolites of pyrrolizidine alkaloids generated in the liver can survive the aqueous environment of the circulatory system as glutathione conjugates or mercapturic acids.

Acetylcysteine↗