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Biomedical subjects

J T Corbett

Publications and source records attributed to J T Corbett.

At least 37 records · Page 2Linked to original sources
PubMed1986

Application of the thiobarbiturate assay to the measurement of lipid peroxidation products in microsomes.

By applying two different thiobarbiturate assay procedures in parallel to aliquots of a microsomal incubation mixture one can simultaneously monitor free malondialdehyde and malondialdehyde plus labile lipid peroxidation products. The levels of malondialdehyde increase continuously during the incubation of microsomes, NADPH and ferrous-ADP complex, while the lipid precursors of MDA stop forming when the system becomes depleted in NADPH. In contrast to systems in which lipids are undergoing autooxidation, NADPH-dependent lipid peroxidation does not appear to generate significant amounts of water-soluble malondialdehyde precursors. As a result, quantitative interpretation of results is straightforward in the microsomal system. In spite of the lack of specificity of the thiobarbiturate coupling reaction, interferences can be easily compensated for by using zero time controls.

Animals↗
PubMed1985

Activation of nonspecific lipase (EC 3.1.1.-) by bile salts.

The enzyme nonspecific lipase (EC 3.1.1.-) from rat pancreas has been isolated and its amino acid composition determined. The amino acid composition confirms more indirect evidence that nonspecific lipase is not the same enzyme as cholesteryl ester hydrolase. Activation of the enzymatic activity by bile salts has been studied by equilibrium dialysis, gel filtration, light scattering, circular dichroism and fluorescence polarization. The binding of bile salt by the enzyme is saturable and is associated with a conformational change. Upon binding cholate, the protein experiences a decrease in beta-structure with no significant change in alpha-helix content, an increase in apparent Stokes radius, a decrease in light scattering properties, and a slight decrease in polarization of the intrinsic tryptophan fluorescence. Attachment of bile salt is associated with decreased reactivity of essential sulfhydryl groups, but no detectable change in reactivity of amino groups. A change to a more nearly spherical shape upon binding bile salt would be consistent with the experimental observations, but the exact sites of binding remain uncertain.

Amino Acids↗
PubMed1984

Metabolism of methyl n-amyl ketone (2-heptanone) and its binding to DNA of rat liver in vivo and in vitro.

Methyl n-amyl ketone (2-heptanone), a reported metabolite of 2-ethylhexanol which in turn is a primary metabolite of plasticizers such as di-(2-ethylhexyl) phthalate, is metabolized in male Fischer 344 rats to CO2, acetate and a variety of compounds that could be either anabolic or catabolic or a combination of the two. A significant percentage of the radioactivity given orally (gavage) as [2-14C]-2 heptanone, at least 10%, was not excreted from the body in 48 h. Radioactivity was incorporated into liver protein in the form of three unidentified products as well as [14C]arginine, and into DNA both as 14C-labeled normal nucleosides (50-75%) and as presently unidentified hydrophobic materials (25-50%). Urea and cholesterol were significantly labeled, indicative of anabolic reutilization of [2-14C]-2-heptanone breakdown products. The 2-heptanone also bound to DNA spontaneously in vitro, to the extent of 400 pmol/mg DNA.

Animals↗
PubMed1984

Urinary metabolites of orally administered di-(5-hexenyl) phthalate and di-(9-decenyl) phthalate in the rat.

Di-(5-hexenyl)- and di-(9-decenyl) phthalates were administered to male CD rats by gavage. The urinary metabolites retaining the phthalate moiety were identified by chromatographic and mass-spectrometric techniques. Di-(5-hexenyl) phthalate gave rise to epoxide and vicinal diol metabolites not previously seen with phthalic acid esters of saturated alcohols. Neither epoxide nor diol were detected when di-(9-decenyl) phthalate was fed. The distributions of carboxyl-terminated metabolites suggested that somewhat different pathways were followed for the two test compounds. The formation of epoxides from these unsaturated phthalate esters may have relevance to their potential toxicities. Like the metabolites of di-n-butyl phthalate, the metabolites of di-(5-hexenyl) phthalate included glucuronide conjugates; like the metabolites of di-(2-ethylhexyl) phthalate, those of di-(9-decenyl) phthalate did not.

Administration, Oral↗
PubMed1983

Polar metabolites of di-(2-ethylhexyl)phthalate in the rat.

Di-(2-ethylhexyl)phthalate (DEHP) is an important industrial chemical widely used as a plasticizer for vinyl and other plastics. DEHP is extensively metabolized by mammals, different species showing dramatic differences in metabolite distributions. Previous studies of the metabolism in rats led to the suggestion that the enzymatic processes normally associated with omega-, omega-1, alpha-, and beta-oxidation of fatty acids could account for the known metabolites of DEHP found in the urine. Several additional metabolites of DEHP have been identified in the present study. Their formation requires that the initial hydroxylation process be less specific than fatty acid omega- and omega-1 oxidation are thought to be. Furthermore, it is necessary to postulate either that the aliphatic chain of mono-(2-ethylhexyl)phthalate can be oxidized at two sites simultaneously, or that oxidation products can be recycled for a second hydroxylation prior to excretion.

Animals↗
PubMed1982

Chromatographic separation and quantitative determination of the metabolites of di-(2-ethylhexyl) phthalate from urine of laboratory animals.

Free, glycine-conjugated, and glucuronide-conjugated metabolites of di-(2-ethylhexyl) phthalate may be stripped from urine with XAD-2 resin, derivatized, and quantitatively analyzed by liquid chromatography on a nitrile column with UV and/or radioactivity monitors. One class of metabolites requires reversed-phase chromatography or gas-liquid chromatography for its resolution. Relative molar responses of the hydrogen flame-ionization detector to these metabolites have been determined. Packed gas chromatography columns (OV-3, OV-210, cyclohexanedimethanol succinate) and fused-silica capillary columns (SP2100 and FFAP) are useful for quantitative analysis under appropriate conditions. The simplest gas chromatographic procedure permitting complete quantitative analysis requires hydrolysis of conjugates, formation of methyl esters of carboxyl groups, butyration of hydroxyl groups and chromatography on OV-3. Typical distributions of di-(2-ethylhexyl) phthalate metabolites in urine from mice, hamsters, and guinea pigs are presented.

Animals↗
PubMed1982

Applications of isotope differentiation for metabolic studies with di-(2-ethylhexyl) phthalate.

The pervasiveness of the plasticizer di-(2-ethylhexyl) phthalate (DEHP) in the environment and especially in the laboratory results in a background that may cause severe interference with analytical studies. Animal-to-animal variability in the distribution of DEHP metabolites in excreta normally makes it necessary to use large groups of animals when different treatments are compared. Finally, radioactive tracers are usually considered undesirable for metabolic studies involving human subjects. All of these problems can be overcome through the use of multiple isotopic labels, especially 12C/13C/14C. Examples are given involving rats and monkeys, and applicability to humans is discussed. The principles involved are not limited to any particular class of test compounds. In rats, the competing pathways for metabolism of phthalate esters produce a different distribution of metabolites from a small intravenous dose of DEHP than from a large oral dose.

Administration, Oral↗
PubMed1982

Pharmacokinetics, interactions with macromolecules and species differences in metabolism of DEHP.

The recent long-term carcinogenesis bioassay of di(2-ethylhexyl) phthalate (DEHP) in rats and mice reported by the National Toxicology Program was the first such bioassay to implicate DEHP as a hepatocarcinogen. At the levels of DEHP fed (up to 1.2% of the diet for two years), the livers of the rats would have been exposed to unhydrolyzed diester; this would not have been the case at lower dosages. Extrapolation to lower dosages is therefore questionable. We do not have sufficient pharmacokinetic data in mice to evaluate the dose relationships as yet. Rodents differ conspicuously from primates in their manner of metabolizing DEHP, both in terms of the demand made on the oxidation potential of the liver and in the chemical properties of the major metabolites. The relevance of these differences must be determined before rodent species can be considered models for the effects of DEHP in humans. Radioactivity from carbonyl-labeled DEHP did not associate with purified protein, RNA or DNA from rat liver in vivo. Label from 2-ethyl-(1-14C)-hexyl-labeled DEHP or mono(2-ethylhexyl) phthalate (MEHP) did appear to associate strongly with purified DNA, but label from free 14C-labeled 2-ethylhexanol did not. The apparent binding from DEHP and MEHP was not exchangeable, but was not proven to be covalent. This phenomenon needs additional study.

Absorption↗
PubMed1978

Effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin on lipid profiles in tissue of the Fischer rat.

Female Fischer 344 rats were given single oral doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 10, 50 or 100 microgram/kg, and sacrificed 1, 3, 10, 14 or 21 days later. The fatty livers caused by a sub-lethal dose of TCDD involved a temporary increase in triglyceride and free fatty acid levels, with a persistent decrease in levels of sterol esters. In contrast, the fatty livers resulting from a lethal dose of TCDD involved a large increase in cholesterol esters and free fatty acids, with little change in triglyceride levels. These changes appeared to result in part from damage sustained by lysosomes. TCDD also altered the lipoprotein composition of the serum, the fatty acid composition of various lipid classes in liver and serum, and the ultrastructure of the liver (formation of myeloid bodies). A rapid, dose-dependent effect of TCDD, was the elevation of levels of organic-soluble fluorescent pigment in the heart. This pigment was found to match a previously characterized fraction of lipofuscins in fluorescence spectrum and chromatographic properties. The relatioship of these observations to a possible mechanism of toxicity for TCDD involving radical-induced lipid peroxidation is discussed.

Animals↗
PubMed1971

Continuing education for general practice--analysis of a programme.

General practitioners in the Northampton area were asked to assess the various meetings of a programme of continuing education they had attended between May 1969 and May 1970. Analysis of their replies suggests that meetings which depend on previous study and encourage participation are most likely to be successful.

Attitude of Health Personnel↗
PubMedDate not supplied

Incorporation of radioactivity from labeled Di-(2-ethylhexyl)phthalate into DNA of rat liver in vivo.

Di-(2-ethylhexyl)phthalate (DEHP), when fed at high levels in the diet for two years, is reportedly an hepatocarcinogen to rats and mice. Radioactivity from ethylhexyl-labeled, but not from phthalate-labeled, [14C]-DEHP is associated with highly purified DNA from the livers of treated rats and this radioactivity is not accounted for by assumptions of adsorption, intercalation, attachment to RNA or histones, an impurity in the labeled DEHP, or artifactual binding during sample workup. Spontaneous binding of radioactivity to DNA from either ethylhexyl-labeled DEHP or its total urinary metabolites could not be detected. Although rat liver slices generated all of the known metabolites of DEHP in vitro, no binding to DNA occurred. Administration of dual 3H/14C-labeled DEHP to rats yielded liver DNA whose 3H/14C ratio was inconsistent with the attachment of any reasonable multi-carbon fragment from the ethylhexyl portion to the DNA. The observation that roughly 100 times as high a percentage of the 14C administered was found in urea as in total DNA suggests that the 14C entered DNA through carbamyl phosphate, a precursor of both urea and pyrimidine bases. If this is the case, the association of C-1 from the ethylhexyl portion of DEHP with DNA may not involve alteration of the DNA or genetic damage.

Animals↗
PubMedDate not supplied

Distribution of di- and mono-(2-ethylhexyl) phthalate in human plasma.

The distributions of di-(2-ethylexyl) phthalate and mono-(2-ethylhexyl) phthalate among the protein constituents of human plasma were studied by selective precipitation and chromatographic procedures. The distributions resulting from the leaching of phthalates from blood bags were simulated conveniently by allowing plasma to extract phthalates from coated Celite. More than 80 per cent of the diester was associated with lipoproteins, in the order: LDL greater than VLDL greater than HDL greater than chylomicrons. The remaining diester was apparently adsorbed weakly and nonspecifically to other proteins, including albumin. Mono-(2-ethylhexyl) phthalate was in equilibrium between free in solution and adsorbed to albumin; none was bound to lipoproteins. Extraction of phthalate from Celite into plasma should provide a convenient preparation for toxicity or pharmacokinetic studies.

Chemical Fractionation↗
PubMedDate not supplied

Endogenous lipids of the earthworm Lumbricus terrestris.

Earthworms (Lumbricus terrestris) were given [1-14C]-labeled palmitic acid by gavage on days 0 and 3, and sacrificed on day 7. The distribution of label among lipid classes indicated that glycerides, sterol esters, cerebrosides, sulfatides, phosphatidylethanolamine, phosphatidylserine and (or) phosphatidylinositol, phosphatidylcholine, and sphingomyelin turn over in, or are synthesized by, the earthworm. Free fatty acids still had the highest specific radioactivity of any lipid class at the end of the experiment. Incorporation of label into sterol and hydrocarbon fractions was insignificant and there was no detectable label incorporated into gangliosides. Phosphatidylethanolamine apparently turned over quite slowly compared with other lipid classes, while the cerebroside fraction became highly labeled. Elongation of palmitic acid to stearate and oxidation to CO2 occurred extensively, but there was no evidence for desaturation.

Animals↗