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M T Smith

Publications and source records attributed to M T Smith.

At least 181 records · Page 10Linked to original sources
PubMed1991

Two benzene metabolites, catechol and hydroquinone, produce a synergistic induction of micronuclei and toxicity in cultured human lymphocytes.

A mixture of two benzene metabolites, hydroquinone and catechol, produces a striking synergistic genotoxic response in cultured human lymphocytes. This was demonstrated using an anti-kinetochore antibody modification of the micronucleus assay. Treatment with hydroquinone alone or in combination with phenol produced a 3-fold increase in micronucleated cells over background. Treatment with catechol or phenol alone and in combination produced only minor increases in the number of micronucleated cells. In contrast, simultaneous treatment with equimolar (75 microM) concentrations of hydroquinone and catechol resulted in a greater than 16-fold induction of micronucleated cells. Given an additivity model, 20 additional micronucleated cells would be expected (after correcting for background frequencies), yet 140 were observed. Further analysis revealed that over 90% of the micronucleated cells stained positively for kinetochores, indicating a high probability that these micronuclei contain entire chromosomes. This synergistic response appears to occur only at equimolar levels of hydroquinone and catechol. These results suggest that these metabolites are acting together to disrupt the mitotic spindle and interfere with chromosome segregation. These data provide further support for the hypothesis that multiple metabolites acting in concert are involved in the benzene-induced genotoxicity and leukemia in humans.

Catechols↗
PubMed1991

Mechanisms of benzene carcinogenesis: application of a physiological model of benzene pharmacokinetics and metabolism.

A physiological pharmacokinetic model for benzene, incorporating metabolic transformations, is used to explore why benzene, but not phenol--its primary metabolite--is carcinogenic at many sites in rats. The model has been parametrized using in vitro or in vivo experimental data. Ranges, rather than fixed values, were assigned to the parameters. The model-predicted levels of phenol and hydroquinone in the tissues are consistently higher when phenol, rather than benzene, is administered. This result demonstrates that the differential carcinogenicity of the two compounds is not explainable in the context of this pharmacokinetic analysis. It also indicates that the phenol-hydroquinone pathway alone is unlikely to account for the carcinogenic effects of benzene. Other metabolites must therefore also be involved.

Administration, Inhalation↗
PubMed1991

Potential role of free radicals in benzene-induced myelotoxicity and leukemia.

Occupational exposure to benzene, a major industrial chemical, has been associated with various blood dyscrasias and increased incidence of acute myelogenous leukemia in humans. It is established that benzene requires metabolism to induce its effects. Benzene exposure in humans and animals has also been shown to result in structural and numerical chromosomal aberrations in lymphocytes and bone marrow cells, indicating that benzene is genotoxic. In this review we have attempted to compile the available evidence on the role of increased free radical activity in benzene-induced myelotoxic and leukemogenic effects. Benzene administration to rodents has been associated with increased lipid peroxidation in liver, plasma, and bone marrow, as shown by an increase in the formation of thiobarbituric-acid reactive products that absorb at 535 nm. Benzene administration to rodents also results in increased prostaglandin levels indicating increased arachidonic acid peroxidation. Other evidence includes the fact that bone marrow cells and their microsomal fractions isolated from rodents following benzene-treatment have a higher capacity to form oxygen free radicals. The bone marrow contains several peroxidases, the most prevalent of which is myeloperoxidase. The peroxidatic metabolism of the benzene metabolites, phenol and hydroquinone, results in arachidonic acid peroxidation and oxygen activation to superoxide radicals, respectively. These metabolites, upon co-administration also produce a myelotoxicity similar to that observed with benzene. Recently, we have found that exposure of human promyelocytic leukemia (HL-60) cells (a cell line rich in myeloperoxidase), to the benzene metabolites, hydroquinone and 1,2,4-benzenetriol results in increased steady-state levels of 8-hydroxydeoxyguanosine a marker of oxidative DNA damage. Peroxidatic metabolism of benzene's phenolic metabolites may therefore be responsible for the increased free radical activity and toxicity produced by benzene in bone marrow. We thus hypothesize that free radicals contribute, at least in part, to the toxic and leukemogenic effects of benzene.

Animals↗
PubMed1991

Metabolism of phenylhydroquinone by prostaglandin (H) synthase: possible implications in o-phenylphenol carcinogenesis.

o-Phenylphenol (OPP) and its sodium salt sodium ortho-phenylphenate (NaOPP) are broad spectrum fungicides and antibacterial agents. Both are urinary bladder and renal carcinogens in the Fischer 344 rat. OPP is converted by mixed-function oxidases in the liver to phenylhydroquinone (PHQ). Since appreciable amounts of prostaglandin (H) synthase (PGS) are found in rat bladder and kidney-medullary papilla, the target sites of OPP- and NaOPP-induced tumors, we hypothesized that a secondary PGS-mediated activation of PHQ to phenylbenzoquinone (PBQ) may occur in the bladder and kidney. We have studied the metabolism of PHQ by PGS in the presence of arachidonic acid and hydrogen peroxide as co-factors. These studies showed that PHQ is indeed metabolized to a product having identical spectral and electrochemical properties to PBQ. The disappearance of PHQ with time was stoichiometric to the formation of PBQ. Less than 10% of PHQ was converted to PBQ in the absence of enzyme, indicating that auto-oxidation may play only a minor role in the conversion of PHQ to PBQ. Similar results were obtained when PGS was replaced with either myeloperoxidase or horseradish peroxidase and hydrogen peroxide as co-factor. These studies suggest that the peroxidative metabolism of PHQ by PGS to the reactive PBQ could play an important role in OPP-induced urinary bladder and kidney carcinogenesis in rats.

Animals↗
PubMed1991

Quantitation of oxycodone in human plasma using high-performance liquid chromatography with electrochemical detection.

An original, highly sensitive and specific high-performance liquid chromatographic (HPLC) assay has been developed for the measurement of oxycodone in human plasma with a detection limit of 10 ng/ml using a 1.0-ml plasma sample. Plasma samples were initially acid-washed and then extracted twice at pH 10 with butyl chloride. Oxycodone and codeine (internal standard) were eluted with a mixture of methanol, acetonitrile, and 0.01 M pH 7 phosphate buffer to which 40 mg/l of cetyltrimethylammonium bromide (cetavlon) was added at ambient temperature and detected with electrochemical detection. The addition of cetavlon to the mobile phase markedly reduced the interaction between oxycodone and Si-OH groups on the stationary phase of the HPLC column, so that the organic content of the mobile phase could be reduced from 80 to 25%. Quantitation was achieved using the peak height ratio of oxycodone to codeine. The assay is currently being used for the study of oxycodone pharmacokinetics after single oral doses of 10 and 20 mg and single rectal doses of 30 mg.

Administration, Oral↗
PubMed1991

Human somatic mutation assays as biomarkers of carcinogenesis.

This paper describes four assays that detect somatic gene mutations in humans: the hypoxanthine-guanine phosphoribosyl transferase assay, the glycophorin A assay, the HLA-A assay, and the sickle cell hemoglobin assay. Somatic gene mutation can be considered a biomarker of carcinogenesis, and assays for somatic mutation may assist epidemiologists in studies that attempt to identify factors associated with increased risks of cancer. Practical aspects of the use of these assays are discussed.

Biomarkers↗
PubMed1991

Hydroxylation of phenol to hydroquinone catalyzed by a human myeloperoxidase-superoxide complex: possible implications in benzene-induced myelotoxicity.

Benzene, a known human myelotoxin and leukemogen is metabolized by liver cytochrome P-450 monooxygenase to phenol. Further hydroxylation of phenol by cytochrome P-450 monooxygenase results in the formation of mainly hydroquinone, which accumulates in the bone marrow. Bone marrow contains high levels of myeloperoxidase. Here we report that phenol hydroxylation to hydroquinone is also catalyzed by human myeloperoxidase in the presence of a superoxide anion radical generating system, hypoxanthine and xanthine oxidase. No hydroquinone formation was detected in the absence of myeloperoxidase. At low concentrations superoxide dismutase stimulated, but at high concentrations inhibited, the conversion of phenol to hydroquinone. The inhibitory effect at high superoxide dismutase concentrations indicates that the active hydroxylating species of myeloperoxidase is not derived from its interaction with hydrogen peroxide. Furthermore, catalase a hydrogen peroxide scavenger, was found to have no significant effect on hydroxylation of phenol to hydroquinone, supporting the lack of hydrogen peroxide involvement. Mannitol (a hydroxyl radical scavenger) was found to have no inhibitory effect, but histidine (a singlet oxygen scavenger) inhibited hydroquinone formation. Based on these results we postulate that a myeloperoxidase-superoxide complex spontaneously rearranges to generate singlet oxygen and that this singlet oxygen is responsible for phenol hydroxylation to hydroquinone. These results also suggest that myeloperoxidase dependent hydroquinone formation could play a role in the production and accumulation of hydroquinone in bone marrow, the target organ of benzene-induced myelotoxicity.

Benzene↗
PubMed1990

Relationships between the mitochondrial transmembrane potential, ATP concentration, and cytotoxicity in isolated rat hepatocytes.

The relationships between mitochondrial transmembrane potential, ATP concentration, and cytotoxicity were evaluated after exposure of isolated rat hepatocytes to different mitochondrial poisons. Both the neurotoxicant 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and its fully oxidized metabolite, the 1-methyl-4-phenylpyridinium (MPP+) ion, caused a concentration- and time-dependent depolarization of mitochondrial membranes which followed ATP depletion and preceded cytotoxicity. The effect of MPTP, but not that of MPP+, was prevented by deprenyl, an inhibitor of MPTP conversion to MPP+ via monoamine oxidase type B. Addition of fructose to the hepatocyte incubations treated with either MPTP or MPP+ counteracted the loss of mitochondrial transmembrane potential. Fructose was also effective in protecting against the mitochondrial membrane depolarization as well as ATP depletion and cytotoxicity induced by antimycin. A, carbonyl cyanide p-trifluoromethoxyphenyl hydrazone, and valinomycin. Data confirm the key role played by MPP(+)-induced mitochondrial damage in MPTP toxicity and indicate that (i) ATP produced via the glycolytic pathway can be utilized by hepatocytes to maintain mitochondrial electrochemical gradient, and (ii) a loss of mitochondrial membrane potential may occur only when supplies of ATP are depleted.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1990

Phenol-induced stimulation of hydroquinone bioactivation in mouse bone marrow in vivo: possible implications in benzene myelotoxicity.

The coadministration of phenol and hydroquinone has been shown to produce myelotoxicity in mice similar to that observed following benzene exposure. One explanation of this phenomenon may be that phenol enhances the peroxidase-dependent metabolic activation of hydroquinone in the mouse bone marrow. Here we report that radiolabeled [14C]hydroquinone and [14C]phenol bind covalently to tissue macromolecules of blood, bone marrow, liver and kidney, when administered intraperitoneally to the mouse in vivo. Substantially more radiolabeled hydroquinone was covalently bound 18 h after administration as compared with that bound after 4 h. Phenol, when administered together with [14C]hydroquinone, significantly stimulated the covalent binding of [14C]hydroquinone oxidation products to blood (P less than 0.001) and bone marrow (P less than 0.05) macromolecules, but had no significant effect on covalent binding of [14C]hydroquinone oxidation products to liver and kidney macromolecules (P greater than 0.05). Catechol, on the other hand, had no effect on the binding of [14C]hydroquinone oxidation products in either bone marrow, kidney or liver (P greater than 0.05). When hydroquinone was administered together with [14C]phenol, a stimulation of the covalent binding of phenol oxidation products to bone marrow macromolecules also occurred (P less than 0.05). In addition, hydroquinone co-administration increased the covalent binding of [14C]phenol oxidation products in kidney and blood (P less than 0.05), but significantly decreased the covalent binding in liver (P less than 0.05). These results suggest that altered pharmacokinetics play a major role in the hydroquinone-dependent stimulation of covalent binding of [14C]phenol oxidation products to extrahepatic tissue macromolecules in vivo. The mechanism underlying the phenol-induced stimulation of binding of [14C]hydroquinone by phenol in blood and bone marrow remains unclear, but stimulation of peroxidase-mediated hydroquinone metabolism may be responsible. The latter may therefore play an important role in benzene-induced myelotoxicity.

Animals↗
PubMed1990

Characterization of micronuclei induced in human lymphocytes by benzene metabolites.

Benzene is an established human leukemogen. Workers occupationally exposed to benzene exhibit increased frequencies of both structural and numerical chromosomal aberrations in their peripheral blood lymphocytes. The metabolite(s) responsible for these chromosomal aberrations has not yet been identified. Using a modified micronucleus assay, we have examined the ability of the metabolites of benzene to induce chromosomal damage in human lymphocytes. An antikinetochore antibody was used to distinguish micronuclei that have a high probability of containing a whole chromosome (kinetochore positive) from those containing acentric fragments (kinetochore negative). In vitro treatments with the benzene metabolites hydroquinone, 1,4-benzoquinone, phenol, and catechol resulted in significant increases in micronuclei formation. Phenol, catechol, and 1,4-benzoquinone treatments resulted in moderate (2- to 5-fold) increases in micronuclei, whereas hydroquinone treatments resulted in a larger (11-fold) increase in micronuclei. Significant dose-related increases in kinetochore-positive micronucleated cells were not observed following 1,4-benzoquinone treatment but were observed following treatment with phenol, catechol, and hydroquinone. The higher efficacy of hydroquinone in inducing both total micronuclei and kinetochore-positive micronucleated cells when compared with catechol, phenol, and 1,4-benzoquinone suggests that hydroquinone is a major contributor to the clastogenicity and aneuploidy observed in the lymphocytes of benzene-exposed workers. Other metabolites may also contribute, however, to the genotoxic effects of benzene. Since consistent chromosomal aberrations are often observed in human leukemias, the ability of the phenolic metabolites of benzene to induce chromosomal damage in human cells also implicates them in benzene-induced leukemia.

Adult↗
PubMed1990

Morphine-3-glucuronide--a potent antagonist of morphine analgesia.

In this study, morphine-3-glucuronide (M3G), the major plasma and urinary metabolite of morphine, was shown to be a potent antagonist of morphine analgesia when administered to rats by the intra-cerebroventricular (i.c.v.) route. The antagonism of morphine analgesia was observed irrespective of whether i.c.v. M3G (2.5 or 3.0 micrograms) was administered 15 mins prior to or 15 mins after i.c.v. morphine (20 micrograms). When M3G (10mg) was administered intraperitoneally (i.p.) to rats 30-40 mins prior to morphine (1.5mg i.p.), the analgesic response was significantly reduced compared to administration of morphine (1.5mg i.p.) alone. It was further demonstrated that i.c.v. M3G (2.0 micrograms) antagonized the analgesic effects of subsequently administered i.c.v. morphine-6-glucuronide (0.25 micrograms).

Analgesia↗
PubMed1990

Dose-dependent pharmacokinetics of caffeine in humans: relevance as a test of quantitative liver function.

Caffeine clearance was determined in 13 healthy control subjects and in 13 patients with histologically proven cirrhosis. On separate occasions, 70 mg, 200 mg, and 300 mg single doses of anhydrous caffeine were administered orally with decaffeinated coffee to each subject. Subjects were analyzed individually, acting as their own controls, thus reducing interindividual variability. The present study showed that caffeine exhibited dose-dependent pharmacokinetics, particularly in subjects who showed high initial clearance with the low dose (70 mg) of caffeine. There was a significant decrease in caffeine clearance with increasing dose from 70 mg to 300 mg (n = 26, p less than 0.01, Dunnett's test), indicating saturable caffeine metabolism in the dose range tested. These findings imply that if caffeine is to be used as a guide to deteriorating liver function, serial caffeine clearance estimations should be performed in each individual subject, with use of the same dose of caffeine each time.

Administration, Oral↗
PubMed1990

Analysis of styrene oxide-globin adducts based upon reaction with Raney nickel.

A new method has been developed for determination of styrene oxide-globin adducts. The technique takes advantage of the reaction between alkylated globin and Raney nickel, which cleaves the carbon-sulfur bond in the styrene oxide-cysteine adduct to form 1-phenylethanol (1-PE) and 2-phenylethanol (2-PE). These alcohols are then reacted with pentafluorobenzoyl chloride and analyzed by GC-ECD. The method appears useful for biological monitoring of individuals exposed to styrene and, potentially, to other chemicals or their electrophilic metabolites which can react with cysteine residues in available proteins. The detection limit of the method, which is 0.04 nmol adducts/sample, indicates that it should be possible to detect adducts in the blood of people who are occupationally exposed to at least 18 mg/m3 of styrene. Analysis of globin from human whole blood which had been modified with [14C]styrene oxide indicated that 6% of the total globin adducts were detected. The method was applied to human and rat blood which had been treated with styrene oxide in vitro and to blood from rats given a single i.p. dose of styrene in vivo. Results from these experiments indicate that 77 times more adducts were detected at a given dose from rat globin than from human globin and that only 0.015% of the styrene dose was bioavailable as styrene oxide in the blood of rats. The reaction with Raney nickel is conducted at 5 degrees C to minimize unfavorable side reactions, such as degradation of 1- and 2-PE and conversion of styrene glycol to 1- and 2-PE. The optimal amount of Raney nickel was found to be 5-6 g/g globin. Since the recovery of 1-PE was not reproducible, only 2-PE is used for quantitation.

Animals↗