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Title: Quinones as toxic metabolites of benzene

Abstract

Occupational exposure to benzene has long been associated with toxicity to the blood and bone marrow, including lymphocytopenia, pancytopenia, aplastic anemia, acute myelogenous leukemia, and possible lymphoma. A variety of studies have established that benzene itself is not the toxic species but requires metabolism to reactive intermediates. The bioactivation of benzene is complex. Both primary and secondary oxidation of benzene and its metabolites are mediated via cytochrome P-450 in the liver, although the role of secondary metabolism in the bone marrow is not clear. Toxicity is associated with the dihydroxy metabolites, hydroquinone and catechol, which concentrate in bone marrow. Hydroquinone and its terminal oxidation product, p-benzoquinone, have been demonstrated to be potent suppressors of cell growth in culture. Suppression of lymphocyte blastogenesis by these compounds is a sulfhydryl-dependent process and occurs at concentrations that do not result in cell death, or in detectable alterations in energy metabolism, intracellular glutathione concentration, or protein synthesis. Recent studies suggest that these compounds and other membrane-penetrating sulfyhdryl alkylating agents, such as N-ethylmaleimide and cytochalasin A, and endogenous regulatory molecules, such as soluble immune response suppressor (SIRS), interfere with microtubule assembly in vitro and selectively interfere with microtubule-dependent cell functions at identical concentrations. These agentsmore » appear to react with nucleophilic sulfhydryl groups essential for guanosine triphosphate binding to tubulin that are particularly sensitive to sulfhydryl-alkylating agents.« less

Authors:
Publication Date:
Research Org.:
Chemical Industry Institute of Toxicology, Research Triangle Park, NC
OSTI Identifier:
5583209
Resource Type:
Journal Article
Resource Relation:
Journal Name: J. Toxicol. Environ. Health; (United States); Journal Volume: 16:5
Country of Publication:
United States
Language:
English
Subject:
63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.; BENZENE; METABOLIC ACTIVATION; OCCUPATIONAL EXPOSURE; LYMPHOCYTES; INHIBITION; QUINONES; TOXICITY; BONE MARROW; CELL CULTURES; CYTOCHROMES; METABOLITES; ANIMAL CELLS; ANIMAL TISSUES; AROMATICS; BIOLOGICAL MATERIALS; BLOOD; BLOOD CELLS; BODY; BODY FLUIDS; CONNECTIVE TISSUE CELLS; HEMATOPOIETIC SYSTEM; HYDROCARBONS; LEUKOCYTES; MATERIALS; ORGANIC COMPOUNDS; ORGANIC OXYGEN COMPOUNDS; ORGANS; PIGMENTS; PROTEINS; SOMATIC CELLS; TISSUES; 560301* - Chemicals Metabolism & Toxicology- Cells- (-1987)

Citation Formats

Irons, R.D. Quinones as toxic metabolites of benzene. United States: N. p., 1985. Web. doi:10.1080/15287398509530777.
Irons, R.D. Quinones as toxic metabolites of benzene. United States. doi:10.1080/15287398509530777.
Irons, R.D. Tue . "Quinones as toxic metabolites of benzene". United States. doi:10.1080/15287398509530777.
@article{osti_5583209,
title = {Quinones as toxic metabolites of benzene},
author = {Irons, R.D.},
abstractNote = {Occupational exposure to benzene has long been associated with toxicity to the blood and bone marrow, including lymphocytopenia, pancytopenia, aplastic anemia, acute myelogenous leukemia, and possible lymphoma. A variety of studies have established that benzene itself is not the toxic species but requires metabolism to reactive intermediates. The bioactivation of benzene is complex. Both primary and secondary oxidation of benzene and its metabolites are mediated via cytochrome P-450 in the liver, although the role of secondary metabolism in the bone marrow is not clear. Toxicity is associated with the dihydroxy metabolites, hydroquinone and catechol, which concentrate in bone marrow. Hydroquinone and its terminal oxidation product, p-benzoquinone, have been demonstrated to be potent suppressors of cell growth in culture. Suppression of lymphocyte blastogenesis by these compounds is a sulfhydryl-dependent process and occurs at concentrations that do not result in cell death, or in detectable alterations in energy metabolism, intracellular glutathione concentration, or protein synthesis. Recent studies suggest that these compounds and other membrane-penetrating sulfyhdryl alkylating agents, such as N-ethylmaleimide and cytochalasin A, and endogenous regulatory molecules, such as soluble immune response suppressor (SIRS), interfere with microtubule assembly in vitro and selectively interfere with microtubule-dependent cell functions at identical concentrations. These agents appear to react with nucleophilic sulfhydryl groups essential for guanosine triphosphate binding to tubulin that are particularly sensitive to sulfhydryl-alkylating agents.},
doi = {10.1080/15287398509530777},
journal = {J. Toxicol. Environ. Health; (United States)},
number = ,
volume = 16:5,
place = {United States},
year = {Tue Jan 01 00:00:00 EST 1985},
month = {Tue Jan 01 00:00:00 EST 1985}
}
  • The role of cell-specific metabolism in benzene toxicity was examined in both murine and human bone marrow. Hemopoietic progenitor cells and stromal cells are important control points for regulation of hemopoiesis. We show that the selective toxicity of hydroquinone at the level of the macrophage in murine bone marrow stroma may be explained by a high peroxidase/nicotanimicle adenine dinucleotide phosphate, reduced [NAD(P)H]:quinone oxidoreductase (NQO1) ratio. Peroxidases metabolize hydroquinone to the reactive 1,4-benzoquinone, whereas NQO1 reduces the quinones formed, resulting in detoxification. Peroxidase and NQO1 activity in human stromal cultures vary as a function of time in culture, with peroxidase activitymore » decreasing and NQO1 activity increasing with time. Peroxidase activity and, more specifically, myeloperoxidase, which had previously been considered to be expressed at the promyelocyte level, was detected in murine lineage-negative and human CD34{sup +} progenitor cells. This provides a metabolic mechanism whereby phenolic metabolites of benzene can be bioactivated in progenitor cells, which are considered initial target cells for the development of leukemias. Consequences of a high peroxidase/NQO1 ratio in HL-60 cells were shown to include hydroquinone-induced apoptosis. Hydroquinone can also inhibit proteases known to play a role in induction of apoptosis, suggesting that it may be able to inhibit apoptosis induced by other stimuli. Modulation of apoptosis may lead to aberrant hemopoiesis and neoplastic progression. This enzyme-directed approach has identified target cells of the phenolic metabolites of benzene in bone marrow and provided a metabolic basis for benzene-induced toxicity at the level of the progenitor cell in both murine and human bone marrow. 60 refs., 8 figs.« less
  • A series of putative metabolites and related analogs of benzene, derived from the valence tautomers benzene oxide and oxepin, was tested for mutagenicity (reversions to histidine prototrophy and forward mutations to resistance to 8-azaguanine) and for cytotoxicity by the Ames Salmonella mutagenicity test. Benzene was not mutagenic in either assay. The benzene oxide-oxepin system and benzene dihydrodial induced point mutations but not frameshifts. 4,5-sym-Oxepin oxide, which is a putative metabolite of the oxepin valence tautomer; 3,6-diazo-cyclohexane-1,6-3,4-dioxide, a synthetic precursor of sym-oxepin oxide; and transoid-4,11-dioxatricyclo(5.1 0)undeca-1,6-diene, a stable bridgehead diene analog of sym-oxepin oxide, were toxic but not mutagenic in bothmore » assays. 4H-Pyran-4-=carboxaldehyde, a stable acid catalyzed rearrangement product of sym-oxepin oxide, was not mutagenic and much less cytotoxic than sym-oxepin oxide. Stable analogs of the valence tautomer benzene oxide, namely syn-indan-3a,7a-oxide and syn-2-hydroxyindan-3a,7a-oxide, were mutagenic and induced point mutations. All compounds were cytotoxic to Salmonella. Firstly, the apparent decay times of these chemicals, especially that of sym-oxepin oxide, were surprisingly longer than expected, as judged by quantitative plate diffusion assays. Secondly, it is concluded that if benzene oxide is further metabolized in its oxepin tautomeric form, toxic but not mutagenic products are formed. Thirdly, the relatively weak mutagenicity of benzene oxide may be mainly due to its instability and corresponding low probability to reach intracellular polynucleotide targets, whereas stable analogs of benzene oxide are relatively more potent mutagens. 48 refs., 4 figs., 3 tabs.« less
  • The effects of benzene and its metabolites on the rate of DNA synthesis were measured in the mouse lymphoma cell line, L5178YS. The direct toxicity of benzene could be distinguished from that of its metabolites since bioactivation of benzene in L5178YS cells was not observed. Cells were exposed to benzene, phenol, catechol, hydroquinone, p-benzoquinone, or 1,2,4-benzenetriol over the range of 1.0 X 10(-7) to 1.0 X 10(-2) M for 30 min, and the rate of DNA synthesis was measured at various times after chemical washout. Cell viability and protein synthesis were determined by trypan blue dye exclusion and (3H)leucine incorporation,more » respectively. Effects were designated as DNA specific when DNA synthesis was inhibited in the absence of discernible effects on cell membrane integrity and protein synthesis. Concentrations of benzene as high as 1 mM had no effect on DNA synthesis. Comparison of the effects at the maximum nontoxic dose for each compound showed that catechol and hydroquinone were the most effective, inhibiting DNA synthesis by 65%. Phenol, benzoquinone, and benzenetriol inhibited DNA synthesis by approximately 40%. Maximum inhibition was observed 60 min after metabolite washout in each case. Benzoquinone was the most potent inhibitor of DNA synthesis, followed by hydroquinone, benzenetriol, catechol, and phenol with ED50 values of 5 X 10(-6), 1 X 10(-5), 1.8 X 10(-4), 2.5 X 10(-4), and 8.0 X 10(-4), respectively. Cyclic voltammetric experiments were performed on the hydroxylated metabolites of benzene to assess the possible involvement of a redox-type mechanism in their inhibition of DNA synthesis. The ease of oxidation of these metabolites correlated with their ED50 values for inhibition of DNA synthesis (r = 0.997). This suggests that oxidation of phenol or one of its metabolites may be necessary for production of the species involved in inhibition of DNA synthesis.« less
  • A method utilizing reverse isotope dilution for the analysis of benzene and its organic soluble metabolites in tissues of rats and mice is presented. Tissues from rats and mice that had been exposed to radiolabeled benzene were extracted with ethyl acetate containing known, excess quantities of unlabeled benzene and metabolites. Butylated hydroxytoluene was added as an antioxidant. The ethyl acetate extracts were analyzed with semipreparative reversed-phase HPLC. Isolated peaks were collected and analyzed for radioactivity (by liquid scintillation spectrometry) and for mass (by UV absorption). The total amount of each compound present was calculated from the mass dilution of themore » radiolabeled isotope. This method has the advantages of high sensitivity, because of the high specific activity of benzene, and relative stability of the analyses, because of the addition of large amounts of unlabeled carrier analogue.« less