1
|
Sex Difference and Benzene Exposure: Does It Matter? INTERNATIONAL JOURNAL OF ENVIRONMENTAL RESEARCH AND PUBLIC HEALTH 2022; 19:ijerph19042339. [PMID: 35206525 PMCID: PMC8872447 DOI: 10.3390/ijerph19042339] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/28/2021] [Revised: 02/15/2022] [Accepted: 02/16/2022] [Indexed: 11/16/2022]
Abstract
Sex-related biological differences might lead to different effects in women and men when they are exposed to risk factors. A scoping review was carried out to understand if sex could be a discriminant in health outcomes due to benzene. Studies on both animals and humans were collected. In vivo surveys, focusing on genotoxicity, hematotoxicity and effects on metabolism suggested a higher involvement of male animals (mice or rats) in adverse health effects. Conversely, the studies on humans, focused on the alteration of blood parameters, myeloid leukemia incidence and biomarker rates, highlighted that, overall, women had significantly higher risk for blood system effects and a metabolization of benzene 23-26% higher than men, considering a similar exposure situation. This opposite trend highlights that the extrapolation of in vivo findings to human risk assessment should be taken with caution. However, it is clear that sex is a physiological parameter to consider in benzene exposure and its health effects. The topic of sex difference linked to benzene in human exposure needs further research, with more numerous samples, to obtain a higher strength of data and more indicative findings. Sex factor, and gender, could have significant impacts on occupational exposures and their health effects, even if there are still uncertainties and gaps that need to be filled.
Collapse
|
2
|
Salehi B, Mishra AP, Shukla I, Sharifi-Rad M, Contreras MDM, Segura-Carretero A, Fathi H, Nasrabadi NN, Kobarfard F, Sharifi-Rad J. Thymol, thyme, and other plant sources: Health and potential uses. Phytother Res 2018; 32:1688-1706. [DOI: 10.1002/ptr.6109] [Citation(s) in RCA: 205] [Impact Index Per Article: 34.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2017] [Revised: 04/10/2018] [Accepted: 04/11/2018] [Indexed: 01/01/2023]
Affiliation(s)
- Bahare Salehi
- Medical Ethics and Law Research Center; Shahid Beheshti University of Medical Sciences; Tehran Iran
- Student Research Committee; Shahid Beheshti University of Medical Sciences; Tehran Iran
| | - Abhay Prakash Mishra
- Faculty of Pharmaceutical Chemistry; H. N. B. Garhwal University; Srinagar Garhwal 246174 India
| | - Ila Shukla
- Pharmacognosy and Ethnopharmacology Division; CSIR-National Botanical Research Institute; Lucknow 226001 India
| | - Mehdi Sharifi-Rad
- Department of Medical Parasitology; Zabol University of Medical Sciences; Zabol 61663-335 Iran
| | - María del Mar Contreras
- Departamento de Ingeniería Química, Ambiental y de los Materiales; Universidad de Jaén; Jaén Spain
| | - Antonio Segura-Carretero
- Department of Analytical Chemistry, Faculty of Sciences; University of Granada; Avda. Fuentenueva s/n Granada 18071 Spain
- Research and Development Functional Food Centre (CIDAF); Bioregión Building, Health Science Technological Park; Avenida del Conocimiento s /n Granada Spain
| | - Hannane Fathi
- Department of Medicinal Chemistry, School of Pharmacy; Shahid Beheshti University of Medical Sciences; Tehran Iran
| | - Nafiseh Nasri Nasrabadi
- Pharmaceutical Sciences Research Centre, School of Pharmacy; Shahid Beheshti University of Medical Sciences; Tehran Iran
| | - Farzad Kobarfard
- Department of Medicinal Chemistry, School of Pharmacy; Shahid Beheshti University of Medical Sciences; Tehran Iran
- Phytochemistry Research Center; Shahid Beheshti University of Medical Sciences; Tehran Iran
| | - Javad Sharifi-Rad
- Phytochemistry Research Center; Shahid Beheshti University of Medical Sciences; Tehran Iran
- Department of Chemistry, Richardson College for the Environmental Science Complex; The University of Winnipeg; 599 Portage Avenue Winnipeg MB R3B 2G3 Canada
| |
Collapse
|
3
|
Knutsen JS, Kerger BD, Finley B, Paustenbach DJ. A calibrated human PBPK model for benzene inhalation with urinary bladder and bone marrow compartments. RISK ANALYSIS : AN OFFICIAL PUBLICATION OF THE SOCIETY FOR RISK ANALYSIS 2013; 33:1237-1251. [PMID: 23278103 DOI: 10.1111/j.1539-6924.2012.01927.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
A physiologically-based pharmacokinetic (PBPK) model of benzene inhalation based on a recent mouse model was adapted to include bone marrow (target organ) and urinary bladder compartments. Empirical data on human liver microsomal protein levels and linked CYP2E1 activities were incorporated into the model, and metabolite-specific conversion rate parameters were estimated by fitting to human biomonitoring data and adjusting for background levels of urinary metabolites. Human studies of benzene levels in blood and breath, and phenol levels in urine were used to validate the rate of human conversion of benzene to benzene oxide, and urinary benzene metabolites from Chinese benzene worker populations provided model validation for rates of human conversion of benzene to muconic acid (MA) and phenylmercapturic acid (PMA), phenol (PH), catechol (CA), hydroquinone (HQ), and benzenetriol (BT). The calibrated human model reveals that while liver microsomal protein and CYP2E1 activities are lower on average in humans compared to mice, the mouse also shows far lower rates of benzene conversion to MA and PMA, and far higher conversion of benzene to BO/PH, and of BO/PH to CA, HQ, and BT. The model also differed substantially from existing human PBPK models with respect to several metabolic rate parameters of importance to interpreting benzene metabolism and health risks in human populations associated with bone marrow doses. The model provides a new methodological paradigm focused on integrating linked human liver metabolism data and calibration using biomonitoring data, thus allowing for model uncertainty analysis and more rigorous validation.
Collapse
|
4
|
Kolanczyk RC, Schmieder P, Jones WJ, Mekenyan OG, Chapkanov A, Temelkov S, Kotov S, Velikova M, Kamenska V, Vasilev K, Veith GD. MetaPath: An electronic knowledge base for collating, exchanging and analyzing case studies of xenobiotic metabolism. Regul Toxicol Pharmacol 2012; 63:84-96. [DOI: 10.1016/j.yrtph.2012.02.013] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2011] [Revised: 02/22/2012] [Accepted: 02/28/2012] [Indexed: 10/28/2022]
|
5
|
Biotransformation enzyme-dependent formation of micronucleus and multinuclei in cell line V79-hCYP2E1-hSULT1A1 by 2-nitropropane and N-nitrosodimethylamine. MUTATION RESEARCH-GENETIC TOXICOLOGY AND ENVIRONMENTAL MUTAGENESIS 2011; 726:84-7. [DOI: 10.1016/j.mrgentox.2011.08.001] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/20/2011] [Revised: 07/11/2011] [Accepted: 08/16/2011] [Indexed: 11/22/2022]
|
6
|
Wongvijitsuk S, Navasumrit P, Vattanasit U, Parnlob V, Ruchirawat M. Low level occupational exposure to styrene: Its effects on DNA damage and DNA repair. Int J Hyg Environ Health 2011; 214:127-37. [PMID: 21030303 DOI: 10.1016/j.ijheh.2010.09.007] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2010] [Revised: 09/10/2010] [Accepted: 09/27/2010] [Indexed: 11/30/2022]
Affiliation(s)
- Sirilak Wongvijitsuk
- Laboratory of Environmental Toxicology, Chulabhorn Research Institute, Bangkok 10210, Thailand
| | | | | | | | | |
Collapse
|
7
|
A Multicompartment Liver-based Pharmacokinetic Model for Benzene and its Metabolites in Mice. Bull Math Biol 2009; 72:507-40. [DOI: 10.1007/s11538-009-9459-x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2008] [Accepted: 09/14/2009] [Indexed: 11/25/2022]
|
8
|
Wilbur S, Wohlers D, Paikoff S, Keith LS, Faroon O. ATSDR evaluation of health effects of benzene and relevance to public health. Toxicol Ind Health 2009; 24:263-398. [PMID: 19022880 DOI: 10.1177/0748233708090910] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
As part of its mandate, the Agency for Toxic Substances and Disease Registry (ATSDR) prepares toxicological profiles on hazardous chemicals found at Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) National Priorities List (NPL) sites that have the greatest public health impact. These profiles comprehensively summarize toxicological and environmental information. This article constitutes the release of portions of the Toxicological Profile for Benzene. The primary purpose of this article is to provide public health officials, physicians, toxicologists, and other interested individuals and groups with an overall perspective on the toxicology of benzene. It contains descriptions and evaluations of toxicological studies and epidemiological investigations and provides conclusions, where possible, on the relevance of toxicity and toxicokinetic data to public health.
Collapse
Affiliation(s)
- S Wilbur
- Agency for Toxic Substances and Disease Registry (ATSDR), U.S. Department of Health and Human Services, Atlanta, Georgia 30333, USA.
| | | | | | | | | |
Collapse
|
9
|
Mikov I, Mikov A, Siriski J, Mikov M, Milovanov V. Effect of Simultaneous Exposure to Benzene and Ethanol on Urinary Phenol Excretion in Mice. J Occup Health 2006. [DOI: 10.1539/joh.42.258] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Affiliation(s)
| | - Aleksandra Mikov
- Department for Pharmacology, Toxicology and Clinical Pharmacology, Medical Faculty
| | | | - Momir Mikov
- Department for Pharmacology, Toxicology and Clinical Pharmacology, Medical Faculty
| | - Vladan Milovanov
- Institute of Children and Adolescents Health CareNovi SadFRYugoslavia
| |
Collapse
|
10
|
Kim S, Vermeulen R, Waidyanatha S, Johnson BA, Lan Q, Rothman N, Smith MT, Zhang L, Li G, Shen M, Yin S, Rappaport SM. Using urinary biomarkers to elucidate dose-related patterns of human benzene metabolism. Carcinogenesis 2005; 27:772-81. [PMID: 16339183 DOI: 10.1093/carcin/bgi297] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Although the toxicity of benzene has been linked to its metabolism, the dose-related production of metabolites is not well understood in humans, particularly at low levels of exposure. We investigated unmetabolized benzene in urine (UBz) and all major urinary metabolites [phenol (PH), E,E-muconic acid (MA), hydroquinone (HQ) and catechol (CA)] as well as the minor metabolite, S-phenylmercapturic acid (SPMA), in 250 benzene-exposed workers and 139 control workers in Tianjin, China. Median levels of benzene exposure were approximately 1.2 p.p.m. for exposed workers (interquartile range: 0.53-3.34 p.p.m.) and 0.004 p.p.m. for control workers (interquartile range: 0.002-0.007 p.p.m.). (Exposures of control workers to benzene were predicted from levels of benzene in their urine.) Metabolite production was investigated among groups of 30 workers aggregated by their benzene exposures. We found that the urine concentration of each metabolite was consistently elevated when the group's median benzene exposure was at or above the following air concentrations: 0.2 p.p.m. for MA and SPMA, 0.5 p.p.m. for PH and HQ, and 2 p.p.m. for CA. Dose-related production of the four major metabolites and total metabolites (micromol/l/p.p.m. benzene) declined between 2.5 and 26-fold as group median benzene exposures increased between 0.027 and 15.4 p.p.m. Reductions in metabolite production were most pronounced for CA and PH<1 p.p.m., indicating that metabolism favored production of the toxic metabolites, HQ and MA, at low exposures.
Collapse
Affiliation(s)
- Sungkyoon Kim
- School of Public Health, University of North Carolina, Chapel Hill, NC 27599, and National Cancer Institute (NCI), National Institutes of Health (NIH), Department of Health and Human Services (DHHS), Bethesda, MD 20892, USA
| | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
11
|
Abstract
Conjugated alkyphenols in milk constitute a reservoir for species-related alkylphenols in dairy products. The distributions of conjugated alkylphenols between different conjugation pathways (sulfation, phosphorylation, and glucuronidation) were determined in cows', sheep's, and goats' milk. Species-related p- and m-cresols and 3- and 4-ethylphenols were found to be mostly conjugated with sulfate with minor amounts associated with phosphate and glucuronide conjugates in all milks. Similar distributions were observed for alkylphenols in the urine and milk from the same ewe. Phenol was present in minor amounts distributed sporadically between different conjugates in the milks. Sulfate-conjugated phenol was not detected in the ewe's urine, which included equal amounts of glucuronide and phosphate conjugates. The amounts of alkylphenols were different in sheep's milk from different sources suggesting that there were effects of feed, breed, and individual animal variation on the metabolism of alkylphenols.
Collapse
Affiliation(s)
- M Kilic
- Department of Food Engineering, Istanbul Technical University, 34469 Maslak, Turkey.
| | | |
Collapse
|
12
|
Faiola B, Fuller ES, Wong VA, Pluta L, Abernethy DJ, Rose J, Recio L. Exposure of Hematopoietic Stem Cells to Benzene or 1,4-Benzoquinone Induces Gender-Specific Gene Expression. Stem Cells 2004; 22:750-8. [PMID: 15342939 DOI: 10.1634/stemcells.22-5-750] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Chronic exposure to benzene results in progressive decline of hematopoietic function and may lead to the onset of various disorders, including aplastic anemia, myelodysplastic syndrome, and leukemia. Damage to macromolecules resulting from benzene metabolites and misrepair of DNA lesions may lead to changes in hematopoietic stem cells (HSCs) that give rise to leukemic clones. We have shown previously that male mice exposed to benzene by inhalation were significantly more susceptible to benzene-induced toxicities than females. Because HSCs are targets for benzene-induced cytotoxicity and genotoxicity, we investigated DNA damage responses in HSC from both genders of 129/SvJ mice after exposure to 1,4-benzoquinone (BQ) in vitro or benzene in vivo. 1,4-BQ is a highly reactive metabolite of benzene that can cause cellular damage by forming protein and DNA adducts and producing reactive oxygen species. HSCs cultured in the presence of 1,4-BQ for 24 hours showed a gender-independent, dose-dependent cytotoxic response. RNA isolated from 1,4-BQ-treated HSCs and HSCs from mice exposed to 100 ppm benzene by inhalation showed altered expression of apoptosis, DNA repair, cell cycle, and growth control genes compared with unexposed HSCs. Rad51, xpc, and mdm-2 transcript levels were increased in male but not female HSCs exposed to 1,4-BQ. Males exposed to benzene exhibited higher mRNA levels for xpc, ku80, ccng, and wig1. These gene expression differences may partially explain the gender disparity in benzene susceptibility. HSC culture systems such as the one used here will be useful for testing the hematotoxicity of various substances, including other benzene metabolites.
Collapse
MESH Headings
- Animals
- Apoptosis/drug effects
- Apoptosis/genetics
- Benzene/adverse effects
- Benzene/toxicity
- Benzoquinones/adverse effects
- Benzoquinones/toxicity
- Carcinogens/adverse effects
- Carcinogens/toxicity
- Cell Cycle Proteins/drug effects
- Cell Cycle Proteins/genetics
- Cell Transformation, Neoplastic/chemically induced
- Cell Transformation, Neoplastic/genetics
- Cells, Cultured
- DNA Damage/drug effects
- DNA Damage/genetics
- DNA Repair/drug effects
- DNA Repair/genetics
- Dose-Response Relationship, Drug
- Female
- Gene Expression Regulation, Neoplastic/drug effects
- Gene Expression Regulation, Neoplastic/genetics
- Genes, cdc/drug effects
- Genes, cdc/physiology
- Genetic Predisposition to Disease/genetics
- Hematopoietic Stem Cells/drug effects
- Hematopoietic Stem Cells/metabolism
- Leukemia/chemically induced
- Leukemia/genetics
- Male
- Mice
- RNA, Messenger/drug effects
- RNA, Messenger/metabolism
- Sex Characteristics
- Up-Regulation/drug effects
- Up-Regulation/genetics
Collapse
Affiliation(s)
- Brenda Faiola
- CIIT Centers for Health Research, Research Triangle Park, NC, USA.
| | | | | | | | | | | | | |
Collapse
|
13
|
Kolanczyk RC, Schmieder PK. Rate and capacity of hepatic microsomal ring-hydroxylation of phenol to hydroquinone and catechol in rainbow trout (Oncorhynchus mykiss). Toxicology 2002; 176:77-90. [PMID: 12062932 DOI: 10.1016/s0300-483x(02)00144-0] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Rainbow trout (Oncorhynchus mykiss) liver microsomes were used to study the rate of ring-hydroxylation of phenol at 11 and 25 degrees C by directly measuring the production of two potentially toxic metabolites, hydroquinone (HQ) and catechol (CAT). An HPLC method with integrated ultraviolet and electrochemical detection was used for metabolite identification and quantification at low (pmol) formation rates found in fish. The Michaelis-Menten saturation kinetics for the production of HQ and CAT over a range of phenol concentrations were determined at trout physiological pH. The apparent Km's for the production of HQ and CAT at 11 degrees C were 14+/-1 and 10+/-1 mM, respectively, with Vmax's of 552+/-71 and 161+/-15 pmol/min per mg protein. The kinetic parameters for HQ and CAT at 25 degrees C were 22+/-1 and 32+/-3 mM (Km) and 1752+/-175 and 940+/-73 pmol/min per mg protein (Vmax), respectively. The calculated increase in metabolic rate per 10 degrees C temperature rise (Q(10)) was 2.28 for HQ and 3.53 for CAT production. These experiments assess the potential for metabolic bioactivation in fish through direct quantification of putative reactive metabolites at the low, but toxicologically significant, chemical concentrations found in aquatic organisms. This work initiates a series of studies to compare activation pathway, rate, and capacity across fish species, providing a basis for development of biologically-based dose response models in diverse species.
Collapse
Affiliation(s)
- Richard C Kolanczyk
- Mid-Continent Ecology Division, US Environmental Protection Agency, 6201 Congdon Blvd, Duluth, MN 55804, USA.
| | | |
Collapse
|
14
|
Kohlert C, Schindler G, März RW, Abel G, Brinkhaus B, Derendorf H, Gräfe EU, Veit M. Systemic availability and pharmacokinetics of thymol in humans. J Clin Pharmacol 2002; 42:731-7. [PMID: 12092740 DOI: 10.1177/009127002401102678] [Citation(s) in RCA: 109] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Essential oil compounds such as found in thyme extract are established for the therapy of chronic and acute bronchitis. Various pharmacodynamic activities for thyme extract and the essential thyme oil, respectively, have been demonstrated in vitro, but availability of these compounds in the respective target organs has not been proven. Thus, investigation of absorption, distribution, metabolism, and excretion are necessary to provide the link between in vitro effects and in vivo studies. To determine the systemic availability and the pharmacokinetics of thymol after oral application to humans, a clinical trial was carried out in 12 healthy volunteers. Each subject received a single dose of a Bronchipret TP tablet, which is equivalent to 1.08 mg thymol. No thymol could be detected in plasma or urine. However, the metabolites thymol sulfate and thymol glucuronide were found in urine and identified by LC-MS/MS. Plasma and urine samples were analyzed after enzymatic hydrolysis of the metabolites by headspace solid-phase microextraction prior to GC analysis and flame ionization detection. Thymol sulfate, but not thymol glucuronide, was detectable in plasma. Peak plasma concentrations were 93.1+/-24.5 ng ml(-1) and were reached after 2.0+/-0.8 hours. The mean terminal elimination half-life was 10.2 hours. Thymol sulfate was detectable up to 41 hours after administration. Urinary excretion could be followed over 24 hours. The amount of both thymol sulfate and glucuronide excreted in 24-hour urine was 16.2%+/-4.5% of the dose.
Collapse
Affiliation(s)
- Claudia Kohlert
- German Central Institute for Pharmaceutical Research, Sinzig
| | | | | | | | | | | | | | | |
Collapse
|
15
|
Abstract
An experiment clarifying the influence of food deprivation on the isoflavone conjugation pattern in rats was conducted. Food-deprived and fed rats were administered daidzein and genistein at 7.9 mcmol/kg body, and changes in their plasma metabolites (i.e., free compounds, sulfates, glucuronides, sulfates/glucuronides) were measured quantitatively as a function of time. In the food-deprived group, total plasma daidzein and genistein reached maximum concentrations of 20.9 +/- 4.4 and 11.4 +/- 3.1 mcmol/L, respectively, 10 min after administration, whereas in the fed group, the maxima were 2.4 +/- 0.8 mcmol/L for daidzein after 2 h and 1. 8 +/- 0.2 mcmol/L for genistein after 4 h. In both groups, there were significantly more daidzein sulfates than genistein sulfates. Moreover, depriving rats of food before daidzein and genistein administration significantly increased plasma isoflavone sulfates with simultaneous significant decreases in plasma isoflavone glucuronides compared with fed rats. Additionally, nonconjugated daidzein and genistein appeared in plasma of food-deprived rats for 1 h after administration. Plasma concentrations of conjugates having both sulfate and glucuronide moieties were not significantly different between the groups.
Collapse
Affiliation(s)
- M K Piskula
- Noda Institute for Scientific Research, 399 Noda-City, Chiba 278-0037, Japan
| |
Collapse
|
16
|
|
17
|
|
18
|
Medinsky MA, Kenyon EM, Schlosser PM. Benzene: a case study in parent chemical and metabolite interactions. Toxicology 1995; 105:225-33. [PMID: 8571360 DOI: 10.1016/0300-483x(95)03217-4] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Benzene, an important industrial solvent, is also present in unleaded gasoline and cigarette smoke. The hematotoxic effects of benzene in humans are well documented and include aplastic anemia and pancytopenia, and acute myelogenous leukemia. A combination of metabolites (hydroquinone and phenol for example) is apparently necessary to duplicate the hematotoxic effect of benzene, perhaps due in part to the synergistic effect of phenol on myeloperoxidase-mediated oxidation of hydroquinone to the reactive metabolite benzoquinone. Since benzene and its hydroxylated metabolites (phenol, hydroquinone and catechol) are substrates for the same cytochrome P450 enzymes, competitive interactions among the metabolites are possible. In vivo data on metabolite formation by mice exposed to various benzene concentrations are consistent with competitive inhibition of phenol oxidation by benzene. In vitro studies of the metabolic oxidation of benzene, phenol and hydroquinone are consistent with the mechanism of competitive interaction among the metabolites. The dosimetry of benzene and its metabolites in the target tissue, bone marrow, depends on the balance of activation processes such as enzymatic oxidation and deactivation processes such as conjugation and excretion. Phenol, the primary benzene metabolite, can undergo both oxidation and conjugation. Thus, the potential exists for competition among various enzymes for phenol. However, zonal localization of Phase I and Phase II enzymes in various regions of the liver acinus regulates this competition. Biologically-based dosimetry models that incorporate the important determinants of benzene flux, including interactions with other chemicals, will enable prediction of target tissue doses of benzene and metabolites at low exposure concentrations relevant for humans.
Collapse
Affiliation(s)
- M A Medinsky
- Chemical Industry Institute of Toxicology, Research Triangle Park, NC 27709, USA
| | | | | |
Collapse
|