Current concepts of chronic benzene toxicity

Environmental Chemical-Induced Reactive Oxygen Species Generation and Immunotoxicity: A Comprehensive Review

Significance: Reactive oxygen species (ROS), the reactive oxygen-carrying chemicals moieties, act as pleiotropic signal transducers to maintain various biological processes/functions, including immune response. Increased ROS production leads to oxidative stress, which is implicated in xenobiotic-induced adverse effects. Understanding the immunoregulatory mechanisms and immunotoxicity is of interest to developing therapeutics against xenobiotic insults. Recent Advances: While developmental studies have established the essential roles of ROS in the establishment and proper functioning of the immune system, toxicological studies have demonstrated high ROS generation as one of the potential mechanisms of immunotoxicity induced by environmental chemicals, including heavy metals, pesticides, aromatic hydrocarbons (benzene and derivatives), plastics, and nanoparticles. Mitochondrial electron transport and various signaling components, including NADH oxidase, toll-like receptors (TLRs), NF-κB, JNK, NRF2, p53, and STAT3, are involved in xenobiotic-induced ROS generation and immunotoxicity. Critical Issues: With many studies demonstrating the role of ROS and oxidative stress in xenobiotic-induced immunotoxicity, rigorous and orthogonal approaches are needed to achieve in-depth and precise understanding. The association of xenobiotic-induced immunotoxicity with disease susceptibility and progression needs more data acquisition. Furthermore, the general methodology needs to be possibly replaced with high-throughput precise techniques. Future Directions: The progression of xenobiotic-induced immunotoxicity into disease manifestation is not well documented. Immunotoxicological studies about the combination of xenobiotics, age-related sensitivity, and their involvement in human disease incidence and pathogenesis are warranted. Antioxid. Redox Signal. 40, 691-714.

The Key Role of GSH in Keeping the Redox Balance in Mammalian Cells: Mechanisms and Significance of GSH in Detoxification via Formation of Conjugates

Glutathione (GSH) is a ubiquitous tripeptide that is biosynthesized in situ at high concentrations (1-5 mM) and involved in the regulation of cellular homeostasis via multiple mechanisms. The main known action of GSH is its antioxidant capacity, which aids in maintaining the redox cycle of cells. To this end, GSH peroxidases contribute to the scavenging of various forms of ROS and RNS. A generally underestimated mechanism of action of GSH is its direct nucleophilic interaction with electrophilic compounds yielding thioether GSH S-conjugates. Many compounds, including xenobiotics (such as NAPQI, simvastatin, cisplatin, and barbital) and intrinsic compounds (such as menadione, leukotrienes, prostaglandins, and dopamine), form covalent adducts with GSH leading mainly to their detoxification. In the present article, we wish to present the key role and significance of GSH in cellular redox biology. This includes an update on the formation of GSH-S conjugates or GSH adducts with emphasis given to the mechanism of reaction, the dependence on GST (GSH S-transferase), where this conjugation occurs in tissues, and its significance. The uncovering of the GSH adducts' formation enhances our knowledge of the human metabolome. GSH-hematin adducts were recently shown to have been formed spontaneously in multiples isomers at hemolysates, leading to structural destabilization of the endogenous toxin, hematin (free heme), which is derived from the released hemoglobin. Moreover, hemin (the form of oxidized heme) has been found to act through the Kelch-like ECH associated protein 1 (Keap1)-nuclear factor erythroid 2-related factor-2 (Nrf2) signaling pathway as an epigenetic modulator of GSH metabolism. Last but not least, the implications of the genetic defects in GSH metabolism, recorded in hemolytic syndromes, cancer and other pathologies, are presented and discussed under the framework of conceptualizing that GSH S-conjugates could be regarded as signatures of the cellular metabolism in the diseased state.

Machine learning assessment of white blood cell counts in workers exposed to benzene: a historical cohort study

To explore the fitting effect of the ARIMA, GM(1,1), and RANSAC model in the changes of white blood cells (WBC) in benzene-exposed workers, and select the optimal model to predict the WBC count of workers. Among 350 employees in an aerospace process manufacturing enterprise in Nanjing, workers with 10 years of benzene exposure were selected, and used Excel software to organize the WBC data, and the ARIMA model and RANSAC model were established by R software, and the GM(1, 1) model was established by DPS software, and the magnitude of the mean absolute percentage error (MAPE) of fitting three models to WBC counts was compared. The MAPE based on the ARIMA(2,1,2) model is 6.78%, the MAPE based on the GM(1,1) model is 5.19%, and the MAPE based on the RANSAC model is 6.37%, so the GM( 1,1) model was more suitable for fitting the trend of WBC counts in benzene exposed workers in this study. The GM(1,1) model is suitable for fitting WBC counts in a small sample size and can provide a short-term prediction of WBC counts in benzene-exposed workers and provide basic information for occupational health risk assessment of workers.

Violence and the Chemicals Industry: Reframing Regulatory Obstructionism

When government actors seek to restrict the sale of hazardous substances, industry actors tend to intervene, deploying coordinated strategies aimed at delaying, preventing or weakening attempts to regulate their products. In many cases, this has involved deliberate efforts to obfuscate science, mislead the public and manipulate political actors in order to ensure desired policy outcomes. Strategies of regulatory obstructionism have resulted in the prolonged dispersal of harmful chemical substances with tangible impacts on public health. This article proposes that this behavior should be interpreted as a form of violence. Examining the regulatory histories of lead, benzene, asbestos and PCBs, the article demonstrates how regulatory obstructionism and violence have become intractable characteristics of the chemical industry.

Establishment of a zebrafish hematological disease model induced by 1,4-benzoquinone

Benzene exposure is associated with various hematological disorders, in particular leukemia. The reactive metabolite of benzene, 1,4-benzoquinone (BQ), generated in bone marrow, is suggested to be a key molecule in mediating benzene-induced hematotoxicity and carcinogenicity. However, its pathogenic role remains largely unknown due to a lack of suitable vertebrate whole-organism models. Here, we present an in vivo study to reveal the effect of BQ exposure on hematotoxicity in zebrafish. From embryonic stages to adulthood, BQ exposure suppressed erythroid and lymphoid hematopoiesis but led to abnormal accumulation of myeloid cells and precursors, which resembles benzene-induced cytopenia and myeloid dysplasia in humans. This myeloid expansion is caused by granulocyte, but not macrophage, lineage, emphasizing the significant role of lineage specificity in BQ-mediated hematopoietic toxicity. Analysis of the c-myb (also known as myb)-deficient mutant cmyb^hkz3 revealed that BQ induced neutrophilia in a c-myb-dependent manner, demonstrating that c-myb is a key intrinsic mediator of BQ hematotoxicity. Our study reveals that BQ causes lineage-specific hematotoxicity in zebrafish from embryonic stages to adulthood. Since c-myb is indispensable for BQ to induce neutrophilia, c-myb could serve as a potential drug target for reversing BQ hematotoxicity.

Summary: Acute exposure to 1,4-benzoquinone leads to lineage-specific hematotoxicity in zebrafish from embryonic stages to adulthood, resembling benzene-induced cytopenia and myeloid dysplasia in humans.

VNN3, a potential novel biomarker for benzene toxicity, is involved in 1, 4-benzoquinone induced cell proliferation

Benzene is widely employed in the field of production, and its toxicity on biological systems has received increasing attention. Cell proliferation is a major life characteristic of living organisms. KLF15 and NOTCH1 are mature and classical genes in cell proliferation studies, particularly in the area of tumor investigation. The aim of this study was to investigate the effect and mechanism of VNN3 on cell proliferation induced by 1,4-benzoquinone (1,4-BQ), an important metabolite of benzene, and obtain a sensitive biomarker for the hazard screening and health care of benzene exposure. Normally growing AHH-1 cells were cultured in vitro and were incubated with different concentrations of 1,4-BQ (0, 10, 20, and 40 μM) for 24 h. A CCK-8 assay was used to assess the cell viability, whereas EdU was used to detect the cell proliferation of AHH-1 cells. The expression of VNN3, KLF15 and NOTCH1 was detected by real-time PCR. Moreover, a lentiviral model was constructed in AHH-1 cells to interfere with VNN3 expression. The results showed that 1,4-BQ clearly increased the expression of VNN3. Moreover, 1,4-BQ dose-dependently inhibited cell proliferation and caused increased KLF15 expression; in contrast, the NOTCH1 expression decreased in AHH-1 cells. Furthermore, following interference with the VNN3 expression, the cell proliferation inhibition and the expression of KLF15 and NOTCH1 were rescued. To further investigate the action of VNN3 in benzene hematotoxicity, we assessed it in benzene-exposed workers. The results showed that there was a remarkable correlation between the VNN3 expression and hemogram, which included RBC, NEUT and HGB. In addition, analysis of the KLF15 and NOTCH1 expression showed that the VNN3 expression was related to cell proliferation, which was consistent with the in vitro results. In conclusion, VNN3 influences cell proliferation induced by 1,4-BQ by regulating the expression of KLF15 and NOTCH1. VNN3 may represent a potential biomarker of benzene toxicity.

Epidemiology and Toxicology of Volatile Organic Chemical Contaminants in Water Absorbed Through the Skin

This paper provides a general introduction to the occurrence, epidemiology, and toxicity of some of the most common contaminants of water supplies, the volatile organic chemicals (VOCs). The VOCs are formed from the reaction of chlorine during disinfection with naturally occurring carbon in the form of humic acids. The VOCs may also enter water supplies as a result of manufacturing, processing, distribution, and urban and agricultural run off. Their occurrence is summarized in this paper.

No epidemiologic studies examine the health effects where skin is the sole route of exposure. However, in several studies skin is one of the routes of exposure for VOCs. These are summarized in this paper.

Finally, the toxicity of some of the more important VOCs is summarized. Where possible, similarities in toxicity between individual members of this class of chemical contaminants are noted. There are striking similarities of toxicity of various VOCs in the liver, kidney, and hematopoietic system. These similarities should be considered as skin exposure models are being developed.

Leukemia and benzene

Excessive exposure to benzene has been known for more than a century to damage the bone marrow resulting in decreases in the numbers of circulating blood cells, and ultimately, aplastic anemia. Of more recent vintage has been the appreciation that an alternative outcome of benzene exposure has been the development of one or more types of leukemia. While many investigators agree that the array of toxic metabolites, generated in the liver or in the bone marrow, can lead to traumatic bone marrow injury, the more subtle mechanisms leading to leukemia have yet to be critically dissected. This problem appears to have more general interest because of the recognition that so-called "second cancer" that results from prior treatment with alkylating agents to yield tumor remissions, often results in a type of leukemia reminiscent of benzene-induced leukemia. Furthermore, there is a growing literature attempting to characterize the fine structure of the marrow and the identification of so called "niches" that house a variety of stem cells and other types of cells. Some of these "niches" may harbor cells capable of initiating leukemias. The control of stem cell differentiation and proliferation via both inter- and intra-cellular signaling will ultimately determine the fate of these transformed stem cells. The ability of these cells to avoid checkpoints that would prevent them from contributing to the leukemogenic response is an additional area for study. Much of the study of benzene-induced bone marrow damage has concentrated on determining which of the benzene metabolites lead to leukemogenesis. The emphasis now should be directed to understanding how benzene metabolites alter bone marrow cell biology.

Phenolic metabolites of benzene inhibited the erythroid differentiation of K562 cells

Benzene is a common occupational hazard and a ubiquitous environmental pollutant. Benzene exposure at the levels even below 1ppm still showed hematotoxicity. It is widely accepted that the metabolites of benzene play important roles in the benzene toxicity to the hematopoietic system, but little is known about the effects of benzene metabolites on erythropoiesis. In present study, erythroid progenitor-like K562 cells were used to determine the effects of phenolic metabolites of benzene, including phenol, hydroquinone and 1,2,4-benzenetriol, on the erythroid differentiation. After the treatment with these benzene metabolites at the concentrations with no obvious cytotoxicity, the hemin-induced hemoglobin synthesis in K562 cells decreased in a concentration- and time-dependent manner, and the expression of CD71 and GPA protein on the surface of K562 cells was also inhibited. The reverse transcription-PCR was used to determine the mRNA level of the erythroid related genes in the K562 cells that were treated with benzene metabolites. The hemin-induced expression of globin genes, including α-, β- and γ-globin genes, and the gene encoding the heme synthesis enzyme porphobilinogen deaminase was inhibited by benzene metabolites. When the K562 cells were pretreated with benzene metabolites, the hemin-induced expression of two transcription factor genes GATA-1 and NF-E2 was distinctly reduced, and the pre-treatment with benzene metabolites promoted the decrease of the mRNA level of transcription factor gene GATA-2 by hemin. These results indicated that benzene metabolites inhibited the hemin-induced erythroid differentiation through affecting the transcription of the erythroid related genes.

Quinone oxidoreductases in protection against myelogenous hyperplasia and benzene toxicity

Quinone oxidoreductases (NQO1 and NQO2) are cytosolic proteins that catalyze metabolic reduction of quinones and its derivatives to protect cells against redox cycling and oxidative stress. In humans, a high percentage of individuals with myeloid and other types of leukemia are homo- and heterozygous for a null mutant allele of NQO1. The NQO2 locus is also highly polymorphic in humans. Recently, we generated NQO1-/- and NQO2-/- mice deficient in NQO1 and NQO2 protein and activity, respectively. These mice showed no detectable developmental abnormalities and were indistinguishable from wild type mice. Interestingly, all the mice lacking expression of NQO1 and NQO2 protein demonstrated myelogenous hyperplasia of the bone marrow and increased granulocytes in the peripheral blood. Decreased apoptosis contributed to myelogenous hyperplasia. The studies on short-term exposure of NQO1-/- mice to benzene demonstrated substantially greater benzene-induced toxicity, as compared to wild type mice.

Biomarker Research in Occupational Health

OBJECTIVES

A variety of biomarkers have been used to study worker populations, and these studies have achieved different levels of success in the improvement of occupational health.

METHODS

Successful application of biomarker research is dependent upon several important factors: ability to identify hazardous substances from the exposure to a variety of substances, relevance to the development of disease, and usefulness for health risk assessment.

RESULTS

Besides the traditional biomarkers for exposure, biological effects, and health risk, new biomarkers for susceptibility and genome-wide responses are being used to improve our understanding of occupational health at a higher and, perhaps, more precise level.

CONCLUSIONS

In addition, there is a continued need to develop and apply biomarkers that can be used to provide real-time detection of excessive exposure to hazardous substances in the workplace, especially from unexpected fugitive emissions. These topics are discussed in the review.

Xenobiotic Metabolism and the Mechanism(s) of Benzene Toxicity

The investigation of the mechanism(s) of benzene toxicity/leukemogenesis over the past 50 years has been contemporaneous with developments in the study of xenobiotic metabolism. Research on the cytochrome P450 (CYP) enzyme system, and related systems in vivo and in vitro, which culminated in the isolation and reconstitution of the many CYPs, established pathways for the study of xenobiotic metabolism and its relationship to the biological activity of many chemicals. The essential role for metabolism of benzene as a precursor to the demonstration of benzene toxicity led to extensive studies of benzene metabolism, many of which will be reviewed here. Benzene toxicity/leukemogenesis, however, is a function of the bone marrow, a site remote from the liver where most benzene metabolism occurs. Studies of benzene metabolism have delineated the array of metabolites which appear to play a role in bone marrow damage, but further studies, both in vivo and in vitro, using appropriate animal models, will be needed to fully understand the impact of benzene and its metabolites on bone marrow function.

Exposure of Hematopoietic Stem Cells to Benzene or 1,4-Benzoquinone Induces Gender-Specific Gene Expression

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.

Gene expression profile in bone marrow and hematopoietic stem cells in mice exposed to inhaled benzene

Acute myeloid leukemia and chronic lymphocytic leukemia are associated with benzene exposure. In mice, benzene induces chromosomal breaks as a primary mode of genotoxicity in the bone marrow (BM). Benzene-induced DNA lesions can lead to changes in hematopoietic stem cells (HSC) that give rise to leukemic clones. To gain insight into the mechanism of benzene-induced leukemia, we investigated the DNA damage repair and response pathways in total bone marrow and bone marrow fractions enriched for HSC from male 129/SvJ mice exposed to benzene by inhalation. Mice exposed to 100 ppm benzene for 6h per day, 5 days per week for 2 week showed significant hematotoxicity and genotoxicity compared to air-exposed control mice. Benzene exposure did not alter the level of apoptosis in BM or the percentage of HSC in BM. RNA isolated from total BM cells and the enriched HSC fractions from benzene-exposed and air-exposed mice was used for microarray analysis and quantitative real-time RT-PCR. Interestingly, mRNA levels of DNA repair genes representing distinct repair pathways were largely unaffected by benzene exposure, whereas altered mRNA expression of various apoptosis, cell cycle, and growth control genes was observed in samples from benzene-exposed mice. Differences in gene expression profiles were observed between total BM and HSC. Notably, p21 mRNA was highly induced in BM but was not altered in HSC following benzene exposure. The gene expression pattern suggests that HSC isolated immediately following a 2 weeks exposure to 100 ppm benzene were not actively proliferating. Understanding the toxicogenomic profile of the specific target cell population involved in the development of benzene-associated diseases may lead to a better understanding of the mechanism of benzene-induced leukemia and may identify important interindividual and tissue susceptibility factors.

Monitoring of the benzene and toluene contents in human milk

Twenty-three samples of human milk collected from the milk bank of a children's hospital were analysed with a view to monitoring the possible presence of some of the most common aromatic hydrocarbons (benzene and toluene) and to quantify their concentrations. The analysis was carried out by the "purge and trap" technique combined with gas chromatography and with the use of the mass spectrometer as detector. The hydrocarbons themselves were used in a deuterated form as internal standards. The analysis of the data showed the presence of both hydrocarbons, even though their quantity was much lower than that detected in other foods.

Benzene exposure monitoring of Tunisian workers

To monitor benzene exposure and to check reliability of urinary trans,trans-Muconic Acid (t,t-MA) as a bio-marker of benzene exposure in local conditions, a study was conducted on 30 Tunisian exposed workers (20 tanker fillers and 10 filling station attendants). The analyses were carried out on environmental air and urinary t,t-MA before (t,t-MAA) and at the end of work shift (t,t-MAB). 20 nonoccupationally exposed subjects were also investigated. The average value of environmental benzene concentration was 0.17 ppm. The differences between t,t-MAA and t,t-MAB concentrations and between t,t-MAB and t,t-MA measured in controls (t,t-MAC) were both significant (p < 0.001). Benzene air concentrations were well correlated with t,t-MAB: R = 0.76. In the nonexposed group, average t,t-MA concentrations is significantly higher among smokers than nonsmokers (P < 0.02). Analysis of urinary t,t-MA offers a relatively simple and suitable method for benzene exposure monitoring.

Micronucleus formation in mouse bone marrow cells in vivo in response to trans, trans-muconaldehyde

Benzene is a human leukemogen, and a bone marrow toxin and carcinogen in experimental animals. The reactive intermediates involved in benzene toxicity and their mechanism(s) of action have not been clearly delineated. We have investigated the clastogenic and cytotoxic effects of trans,trans-muconaldehyde (MUC), a reactive ring-opened benzene metabolite, in mouse bone marrow cells in vivo. Micronucleus formation was significantly increased when CD-1 mice were treated ip with MUC at 4 and 6 mg/kg/day for two days. These results suggest that leukemogenesis by benzene may be attributable, in part, to MUC-related clastogenic and cytotoxic effects in the bone marrow cells.

Dermal benzene and trichloroethylene induce aneuploidy in immature hematopoietic subpopulations in vivo

Accumulation of genetic damage in long-lived cell populations with proliferative capacity is implicated in tumorigenesis. Hematopoietic stem cells (hsc) maintain lifetime hematopoiesis, and recent studies demonstrate that hsc in leukemic patients are cytogenetically aberrant. We postulated that exposure to agents associated with increased leukemia risk would induce genomic changes in cells in the hsc compartment. Aneusomy involving chromosomes 2 and 11 in sorted hsc (Lin(-)c-kit(+)Sca-1(+)) and maturing lymphoid and myeloid cells from mice that received topical doses of benzene (bz) or trichloroethylene (TCE) was quantified using fluorescence in situ hybridization. Six days after bz or TCE exposure, aneuploid cells in the hsc compartment increase four- to eightfold in a dose- and schedule-independent manner. Aneuploid lymphoid and myeloid cells from bz- and TCE-treated mice approximate controls, except after repeated benzene exposures. Aneuploid cells are more frequent in the hsc compartment than in mature hematopoietic subpopulations. Hematotoxicity was also quantified in bz- and TCE-exposed hematopoietic subpopulations using two colony-forming assays: CFU-GM (colony-forming units/granulocyte-macrophage progenitors) and CAFC (cobblestone area-forming cells). Data indicate that bz is transiently cytotoxic (< or =1 week) to hsc subpopulations, and induces more persistent toxicity (>2 weeks) in maturing, committed progenitor subpopulations. TCE is not hematotoxic at the doses applied. In conclusion, we provide direct evidence for induction of aneuploidy in cells in the hsc compartment by topical exposure to bz and TCE. Disruption of genomic integrity and/or toxicity in hsc subpopulations may be one step in leukemic progression.

NRH:quinone oxidoreductase2 (NQO2)

The quinone oxidoreductases [NAD(P)H:quinone oxidoreductase1 (NQO1) and NRH:quinone oxidoreductase2 (NQO2)] are flavoproteins. NQO1 is known to catalyse metabolic detoxification of quinones and protect cells from redox cycling, oxidative stress and neoplasia. NQO2 is a 231 amino acid protein (25956 mw) that is 43 amino acids shorter than NQO1 at its carboxy-terminus. The human NQO2 cDNA and protein are 54 and 49% similar to the human liver cytosolic NQO1 cDNA and protein. Recent studies have revealed that NQO2 differs from NQO1 in its cofactor requirement. NQO2 uses dihydronicotinamide riboside (NRH) rather than NAD(P)H as an electron donor. Another difference between NQO1 and NQO2 is that NQO2 is resistant to typical inhibitors of NQO1, such as dicoumarol, Cibacron blue and phenindone. Flavones, including quercetin and benzo(a)pyrene, are known inhibitors of NQO2. Even though overlapping substrate specificities have been observed for NQO1 and NQO2, significant differences exist in relative affinities for the various substrates. Analysis of the crystal structure of NQO2 revealed that NQO2 contains a specific metal binding site, which is not present in NQO1. The human NQO2 gene has been precisely localized to chromosome 6p25. The human NQO2 gene locus is highly polymorphic. The NQO2 gene is ubiquitously expressed and induced in response to TCDD. Nucleotide sequence analysis of the NQO2 gene promoter revealed the presence of several cis-elements, including SP1 binding sites, CCAAT box, xenobiotic response element (XRE) and an antioxidant response element (ARE). The complement of these elements regulates tissue specific expression and induction of the NQO2 gene in response to xenobiotics and antioxidants. The in vivo role of NQO2 and its role in quinone detoxification remains unknown.

Species and strain comparisons in the macromolecular binding of extremely low doses of [14C]benzene in rodents, using accelerator mass spectrometry

The kinetics of macromolecular binding of a 5 micrograms/kg body wt dose of [14C]benzene was studied over 48 h in B6C3F1, DBA/2, and C57BL/6 mice and Fischer rats to determine if adduct levels reflect known differences in metabolic capacity, genotoxicity, and carcinogenic potency. Previous studies have suggested that differences in benzene toxicity among strains result from differences in metabolism. Rats and mice were administered [14C]benzene (i.p.), followed by removal of liver and bone marrow at time intervals up to 48 h postexposure. Protein and DNA were isolated and analyzed by accelerator mass spectrometry. Area under the curves for protein and DNA adducts in bone marrow were greatest in B6C3F1 mouse > DBA/2 mouse > C57BL/6 mouse > Fischer rat. These data are consistent with the hypothesis that metabolic capacity contributes to the difference in benzene's carcinogenicity among species. Additionally, these data suggest that target organ adduct levels correlate with tumorigenicity and thus may be indicative of an individuals risk.

Indicators of immunotoxicity in populations of cotton rats (Sigmodon hispidus) inhabiting an abandoned oil refinery

Wildlife species inhabiting contaminated sites are often exposed to complex mixtures of chemicals, many of which have known effects on physiological and biochemical function. Although sensitivity of the immune system to chemical exposure has been documented in laboratory animal and wildlife species, little work has been conducted on feral wildlife populations inhabiting contaminated sites. Immune function was measured in populations of wild cotton rats (Sigmodon hispidus) inhabiting replicated reference and contaminated study sites at an abandoned oil refinery in Oklahoma four times from 1991 to 1992. Several measures of immunocompetence were examined including immune organ mass and cellularity, hematology, in vivo hypersensitivity, macrophage function, killer cell activity, and lymphoproliferative responsiveness. In vitro proliferation of splenocytes, either spontaneous or induced with concanavalin A (Con A), was the most consistent and reliable indicator of immunotoxicity. Spontaneous proliferation of splenocytes was 48 and 24% higher for cotton rats collected from contaminated than reference sites in September 1991 and September 1992, respectively. Likewise, Con A-induced proliferation of splenocytes ranged form 20 to 53% higher in animals collected from contaminated than reference sites in three of four collection periods. The percentage of splenocytes (mean+/-SE) staining positive for Con A receptors was lower on contaminated sites (73.7+/-1.2%) than reference sites (77.0+/-1.4%) in September 1991. Other measures of immune function including macrophage metabolism, hypersensitivity, blood cellularity, and mass and cellularity of immune organs varied between contaminated and reference sites.

Hydroquinone, a reactive metabolite of benzene, inhibits NF-kappa B in primary human CD4+ T lymphocytes

Hydroquinone (HQ), a reactive metabolite of benzene, is present in cigarette smoke and is known to inhibit mitogen-stimulated activation of both T and B lymphocytes. Despite extensive study, the underlying mechanism for HQ's immunotoxicity is not clear. NF-kappa B is a transcription factor known to regulate the expression of a number of genes critical for normal T cell activation. We therefore hypothesized that NF-kappa B might be involved in HQ-induced immunosuppression. In this study, we demonstrate that 1 microM HQ inhibits tumor necrosis factor alpha induced activation of NF-kappa B in primary human CD4+ T cells. This inhibition is not accompanied by a loss in viability, and HQ-treated T cells maintain other active signaling pathways throughout the exposure duration. Additionally, the inhibition of NF-kappa B is reversible as HQ-treated T cells regain normal functioning after 72 h in culture. HQ does not appear to alter NF-kappa B directly as preincubation of nuclear extracts with HQ does not diminish activity of this protein. We further demonstrate that 1 microM HQ inhibits intracellular IL-2 production in T cells stimulated with phorbol ester but does not alter surface expression of CD25 (the alpha-subunit of the IL-2 receptor). These data suggest that NF-kappa B may be an important molecular mediator of HQ's (and benzene's) immunotoxicity.

Scientific update on benzene

The mechanism of benzene toxicity has been extremely difficult to fully characterize. Much progress has been made in assessing the relative potency of benzene metabolites but specific pathways to leukemia remain to be determined. Metabolite and mechanistic studies will have to focus on aplastic anemia and MDS and separate endpoints. This may serve to clarify the array of metabolite effects and consequent disparate effects. Biomarker research can contribute to the understanding of the toxicity process. The significance of understanding benzene toxicity will also lead to better clinical treatment of aplastic anemia and therapy-related MDS and AML, detection of populations particularly susceptible to benzene toxicity, screening of populations with suspected or unknown exposures, and determination of meaningful values for occupational and individual health risk while effectively monitoring ongoing exposures for early signs of toxicity.

Benzene--a review of the literature from a health effects perspective

A literature review of the impact on human health of exposure to benzene was conducted. Special emphasis in this report is given to the health effects reported in excess of national norms by participants in the Benzene Subregistry of the National Exposure Registry--people having documented exposure to benzene through the use of benzene-contaminated water for domestic purposes. The health effects reported in excess (p < or = .01) by some or all of the sex and age groups studied were diabetes, kidney disease, respiratory allergies, skin rashes, and urinary tract disorders; anemia was also increased for females, but not significantly so.

Biodegradation of groundwater pollutants by a combined culture of Mycobacterium vaccae and a Rhodococcus sp

The catabolism of selected groundwater pollutants by a combined culture of Mycobacterium vaccae and a Rhodococcus sp. (strain R-22) was investigated. The M. vaccae-R-22 combined culture was five times more effective in mineralizing benzene than either organism alone. Mycobacterium vaccae oxidized benzene to phenol, and R-22 catabolized the phenol to cellular components and CO2. Benzene did not support growth of M. vaccae, R-22, or the combined culture. Optimization of ratios of the two species indicated that the maximum mineralization of benzene occurred at an initial ratio of 75% M. vaccae to 25% R-22. Cell fractionation of the combined culture after mineralization of [U-14C]benzene indicated that 10% of the benzene carbon was incorporated into cell material, and of this 45% was present in protein and 20% in nucleic acids. This suggested that minimally one species could utilize the products of benzene as a nutrient source. The M. vaccae-R-22 combined culture catabolized ethylbenzene and chlorobenzene without the accumulation of phenolic intermediates, which are inhibitory to M. vaccae's ability to degrade the parent compounds. This study demonstrates that defined mixed cultures may be useful in studying the effects of environmental pollutant degradation on microbial ecosystems and mineralization of these pollutants by the ecosystem.

Positron annihilation spectroscopy and micellar systems

Positron annihilation spectroscopy (PAS) has emerged as a powerful technique for investigating structural changes, phase transitions and microenvironmental transformations in a variety of systems. The process of molecular aggregation in micellar systems is known to be cooperative and size limited; it shows features similar to that of a classical phase transition. Similarly, the changes in the concentration of surfactant and the solubilizate bring about several microstructural and conformational transformations in these systems. High sensitivity of positron annihilation parameters to such changes makes it a potential candidate for investigating micellar and microemulsion systems. This paper deals with this aspect of positron annihilation spectroscopy. Applications of this technique to investigate conformational, structural and microenvironmental transformations in micellar and microemulsion systems are discussed. Its superiority over the conventional techniques in such investigations is demonstrated. It is shown that this technique reveals finer details of otherwise considered to be single phase regions in a phase diagram. Its usefulness in delineating phase boundaries and hence in mapping of phase diagrams is also discussed.

Cellular immune responses of nutritionally stressed juvenile cotton rats (Sigmodon hispidus) during acute benzene exposure

Wild juvenile cotton rats (Sigmodon hispidus) were used in this study to examine the effects of exposure to cyclophosphamide (CY) or differing levels of benzene on selected measures of cellular immunity following dietary protein restriction. Benzene caused marginal immunotoxicity as indicated by suppressed splenocyte proliferation and total circulating neutrophils. Cyclophosphamide and also crude protein restriction induced severe immune lesions manifested as thymus and spleen atrophy, depressed delayed hypersensitivity response, reduced proliferative capacity of splenocytes, and reduced numbers of total leukocytes, lymphocytes, and splenocytes. Although severe immune modulation resulted from the individual effects of CY exposure and dietary protein restriction, there was little statistically significant toxicant-diet interaction.

Praziquantel (antischistosomal drug): is it clastogenic, co-clastogenic or anticlastogenic?

Schistosoma haematobium infection is the most common health problem in Egypt. It is strongly associated with the development of urinary bladder carcinoma. The actual cause for the development of cancer is still under investigations, it can be due to mechanical irritation from schistosomiasis ova, the infection itself or the drugs which are used to treat the patients. Praziquantel (PQ) is a commonly used drug to treat schistosomiasis patients. In mice, an in vivo cytogenetic study showed that PQ is not clastogenic in mice. The frequency of micronuclei in all the study groups were insignificantly different from the control group (p > 0.05). However, it enhanced the clastogenicity of benzene at a very high dose. Results from combined exposure with benzene and PQ showed a significant PQ dose-dependent increase in micronucleus frequency (p < 0.05). A metabolite study revealed that PQ enhanced the metabolism of benzene to form muconaldehyde which may be responsible for the enhancement effect. In schistosomiasis patients, two cytogenetic studies were carried out before and after treatment with PQ. In one of these studies, peripheral blood lymphocytes were examined from schistosomiasis patients to detect chromosomal aberrations (CAs) and micronuclei (MN) before and after treatment with PQ. There was no significant increase in CAs in patients compared with the controls (p > 0.05). The frequency of MN was significantly higher in the infected persons (0.59 +/- 0.44) than the control individuals (0.23 +/- 0.23) (p < 0.05). After treatment, there was no significant change in both parameters. The other study was conducted to determine whether infection with this parasite resulted in an increase of chromosomal breakage, micronuclei, in exfoliated urothelial cells. Micronucleus frequencies were significantly higher in the infected group (mean frequency, 0.84 +/- 0.69%) than among controls (mean frequency, 0.12 +/- 0.21%, p < 0.001). Micronucleus frequencies were higher in infected individuals who smoked compared with those who were non-smokers, although this effect was not significant (p > 0.05). The mean micronucleus frequencies were reduced significantly in the group of patients who were followed up (before treatment, 0.80 +/- 0.70%, after treatment, 0.19 +/- 0.23%, p < 0.001), thus supporting a direct involvement of the infection in increased chromosomal breakage in the urothelium and provide proof of the role of PQ in decreasing the risk of cancer development. At this stage, we still need to study the cytogenetic effect of human exposure to environmental agents such as pesticides, smoking, etc., together with treatment with PQ.

A perspective on benzene leukemogenesis

Although benzene is best known as a compound that causes bone marrow depression leading to aplastic anemia in animals and humans, it also induces acute myelogenous leukemia in humans. The epidemiological evidence for leukemogenesis in humans is contrasted with the results of animal bioassays. This review focuses on several of the problems that face those investigators attempting to unravel the mechanism of benzene-induced leukemogenesis. Benzene metabolism is reviewed with the aim of suggesting metabolites that may play a role in the etiology of the disease. The data relating to the formation of DNA adducts and their potential significance are analyzed. The clastogenic activity of benzene is discussed both in terms of biomarkers of exposure and as a potential indication of leukemogenesis. In addition to chromosome aberrations, sister chromatid exchange, and micronucleus formation, the significance of chromosomal translocations is discussed. The mutagenic activity of benzene metabolites is reviewed and benzene is placed in perspective as a leukemogen with other carcinogens and the lack of leukemogenic activity by compounds of related structure is noted. Finally, a pathway from exposure to benzene to eventual leukemia is discussed in terms of biochemical mechanisms, the role of cytokines and related factors, latency, and expression of leukemia.

Biodegradation and biotransformation of groundwater pollutant mixtures by Mycobacterium vaccae

Mycobacterium vaccae can catabolize a number of major groundwater pollutants. When added singly, acetone, cyclohexane, styrene, benzene, ethylbenzene, propylbenzene, dioxane, and 1,2-dichloroethylene can be catabolized by M. vaccae. Catabolism of a number of these chemicals was monitored by gas-chromatographic analysis. Gas-chromatographic analysis indicated that the products of benzene degradation are phenol and hydroquinone. The products of chlorobenzene and ethylbenzene degradation are 4-chlorophenol and 4-ethylphenol. The extent that some compounds were catabolized when present as mixtures was also investigated. When toluene and benzene were present concomitantly, toluene was catabolized and benzene oxidation was delayed. Although toluene promoted the degradation of styrene, a lower rate of toluene degradation occurred when styrene was present. Both 4-chlorophenol and 4-ethylphenol had an antagonistic effect on the ability of M. vaccae to degrade other aromatic compounds. Studies with [14C]benzene indicated that M. vaccae can mineralize small amounts of this compound. These results suggest that components in mixtures may have a positive or a negative effect on the rates of biodegradation of other pollutants.

Acute cytogenetic effect of benzene on rat bone marrow cells in vivo and the effect of inducers or inhibitors of drug-metabolizing enzymes

Acute cytogenetic effects of benzene in LE rat bone marrow cells in vivo were studied. Chromosome aberrations (CA) induced by benzene consisted mainly of gaps and breaks. Cells with exchanges were rarely observed. The incidence of benzene-induced CA was at its maximum level 12 h after the p.o. or i.p. administration of benzene, dependent on the dose of benzene administered, and higher in male rats than in female rats. However, the sex difference was not observed in the repeated inhalation experiment. Chromosome damage was higher with the p.o. than the i.p. administration. LE rats were more sensitive than Wistar and SD rats to the clastogenic action of benzene. Phenobarbital and Sudan III are well known as inducers of drug-metabolizing enzymes. The peak percentage of benzene-induced CA in the rats pretreated with phenobarbital was observed 6 h after the benzene injection, and it occurred at a higher level than in the rats given only benzene. On the other hand, Sudan III pretreatment suppressed benzene-induced CA at all periods after the benzene injection. SKF-525A (a cytochrome P-450 inhibitor) and cyclohexene oxide (an epoxide hydrase inhibitor) pretreatment also suppressed benzene-induced CA.

Methyl-substitution of benzene and toluene in preparations of human bone marrow

The metabolism of benzene and toluene was investigated in preparations of human bone marrow incubated with S-adenosyl-L-methionine. Benzene undergoes a methyl-substitution reaction to yield toluene as a metabolite. Furthermore, toluene undergoes methyl-substitution in preparations of human bone marrow incubated with S-adenosyl-L-methionine to yield o-xylene, m-xylene, and p-xylene. Metabolites were detected by gas chromatography and mass spectroscopy. No metabolism of either benzene or toluene was detected when a boiled bone marrow preparation was used in the incubation, demonstrating the enzymatic nature of the S-adenosyl-L-methionine dependent methylation of both benzene and toluene.

Synthesis and characterization of deoxyguanosine-benzoquinone adducts

Benzene expresses its carcinogenic potential in humans largely in the form of acute leukemia. Because an understanding of the formation of DNA adducts by benzene metabolites may help to explain the etiological role they play in benzene-induced bone marrow disease, we have synthesized, isolated and characterized adducts formed by the reaction of deoxyguanosine with hydroquinone and p-benzoquinone, two toxic metabolites of benzene. [3H]Deoxyguanosine and [14C]hydroquinone reacted in neutral aqueous buffer containing iron to form two dual-labeled products, which were separated using HPLC. When p-benzoquinone was substituted for hydroquinone, the same adducts were formed in the absence of added iron. The ultraviolet and fluorescence spectra of the less polar adduct, called Adduct 2, were distinctly different from the spectra of the starting materials. NMR and mass spectrometry suggested a compound with a mass of 357 with the p-benzoquinone moiety bound to the N-1 and N2 positions of deoxyguanosine. Based on these data it is proposed that Adduct 2 is (3'OH)benzetheno(1,N2)deoxyguanosine. The more polar product, Adduct 1, was found to have a unique ultraviolet spectrum but did not appear to be fluorescent. Both adducts were observed after calf thymus DNA was incubated with hydroquinone and digested to its constituent nucleosides.

Metabolism and toxicity of trans,trans-muconaldehyde, an open-ring microsomal metabolite of benzene

We have previously hypothesized that ring-opened metabolites may play an important role in benzene toxicity. In this paper we review recent work related to this hypothesis. trans,trans-Muconaldehyde (TTM), a six-carbon diene dialdehyde, was shown by our laboratory to be a microsomal metabolite of benzene. This compound is a ring-opened metabolite of benzene that is hematotoxic in mice. The toxicity of TTM may stem in part from its ability to act as a direct-acting alkylating agent involving interaction with cellular sulfhydryls and/or amino groups. On the other hand, metabolism to the diacid trans,trans-muconic acid (MA), a known urinary metabolite of benzene, may represent detoxification since this results in loss of electrophilicity of the compound. Preliminary results indicate that TTM can be metabolized to MA in vitro and in vivo. The interaction of TTM in vitro with macrophages and neutrophils, key cells in the bone marrow, results in cell membrane changes, including loss of activity in the plasma membrane-bound NADPH-dependent oxidase and decreases in membrane lipid fluidity. Deoxyguanosine also was found to react with TTM, forming several different products. These findings may be due to TTM acting directly as an alkylating agent.

Enhancement of benzene clastogenicity by praziquantel in mice

Praziquantel (PQ) is a commonly used drug to treat patients with schistosomiasis. Previous studies using cells in vitro have shown that PQ can enhance the mutagenic activities of known mutagens. We have conducted a cytogenetic - urine metabolite study to determine the in vivo clastogenic and co-clastogenic potential of PQ with a ubiquitous environmental contaminant, benzene (BZ). 16 groups of adult male ICR mice (5 animals per group) were used. They were negative control, solvent controls (cremophore E1 3%, olive oil and combined), positive control (BZ 440 mg/kg b.w.) and 11 exposed groups. To test for clastogenicity of PQ, mice were treated orally with 100, 400, 800 and 1200 mg/kg b.w. PQ and sacrificed 30 h later for determination of micronuclei (MN) frequency in bone-marrow polychromatic erythrocytes (PCE). None of these PQ does induced an increase of MN frequency. On the other hand, BZ induced, as expected, a high frequency of MN (46.4 +/- 6.34/1000 PCE). The enhancement effect of PQ was tested in 7 groups of mice using 3 different protocols. Mice were treated with 440 mg/kg b.w. BZ and 1 h later with 0, 100, 200, 400, 800 and 1200 mg/kg b.w. PZ. In another group, 800 mg/kg PQ was administered at 3 h after BZ exposure. In the last group, PQ (800 mg/kg) was administered at 1 h prior to BZ exposure. Results from the first combined exposure group showed a significant PQ dose-dependent increase in the frequency of MN in PCE (p less than 0.05). The increase with the two high doses of praziquantel is significantly higher (p less than 0.05) than the MN frequencies in the benzene control and the expected value based on the additive effects of the two agents. Studies with other combined treatment groups showed that the induction of MN was highest when PQ was administered at 1 h before BZ exposure. Moreover, the presence of BZ metabolites (muconic acid, phenol, catechol and hydroquinone) in urine was studied in 6 of the combined treatment groups. This metabolite study revealed that PQ enhanced the metabolism of BZ towards the pathway to form muconaldehyde which is converted to muconic acid in urine. In conclusion, our study showed that PQ is not a clastogen but can enhance the clastogenic activity of BZ in vivo by shifting the metabolic pathways of BZ towards formation of muconaldehyde which may be responsible for the enhancement effect.

Chromosome abnormalities and sister chromatid exchanges in children with acute intoxication due to inhalation of volatile substances

Deliberate inhalation of volatile substances is a common and harmful practice among young persons worldwide. Recently, we described chromosome damage in children who chronically inhale volatile agents. Clinical and cytogenetic studies were performed for 15 "sniffing" children (13 boys and 2 girls), the purpose of which was to define the chromosomal effect of the acute intoxication. A significant increase in the rate of chromosome abnormalities and in the frequency of sister chromatid exchanges (SCEs) was found in sniffers vs. controls. The values were also higher in children who were acutely intoxicated than in those who chronically inhaled volatile agents. Clinical, socioeconomic, and cytogenetic findings are also discussed.

Dermal toxicity of a medium-boiling (154-378 degrees C) coal liquefaction product in the rat--Part I

The subchronic dermal toxicity of a medium-boiling coal liquefaction product (CLP, 154-378 degrees C) was investigated in the rat. CLP was applied to the shaved backs of rats at dose levels of 50, 100, 200, or 400 mg/kg body weight.d, 7 d/wk for a period of 13 wk. Control groups received 0.4 ml/kg of normal saline. Signs of dermal irritation were observed at sites of application in males dosed at 200 and 400 mg/kg body weight and were characterized by thickened, focally necrotic and ulcerative skin. All animals survived the full length of the treatment period. Growth depression was observed in males at all dose levels, but no significant decrease in weight gain was observed in females. An increase in liver/body weight ratios was observed in all treatment groups of both sexes. The organ/body weight ratios for the spleen, heart, kidney, and brain were also increased in the upper dose groups of both sexes. Treatment with CLP caused a dose-dependent decrease in hemoglobin and packed cell volume in both sexes of all dose groups. The number of erythrocytes was decreased and that of neutrophils was increased in some CLP-treated groups of both sexes. There was a mild myeloid hyperplasia with increased myeloid/erythroid ratios in the 200- and 400-mg/kg groups of both sexes. Hepatic microsomal ethoxyresorufin deethylase activity was increased in all treatment groups of females, and in males dosed at 100 mg/kg and higher. In the renal tubules mild treatment-related histological changes occurred, which consisted of eosinophilic inclusions, increased cytoplasmic volume, and pyknosis. These changes were noted in the high-dose groups of both sexes. These data indicate that the medium-boiling CLP could produce systemic toxicity when applied dermally at 50 mg/kg body weight.d.

Toxic effects of benzene and benzene metabolites on mononuclear phagocytes

Benzene is a potent bone marrow toxin in animals and man. Animal studies have shown that exposure to benzene can alter T lymphocyte functions and decrease the resistance of animals to Listeria monocytogenes and transplanted tumor cells. Mononuclear phagocytes participate in host resistance to Listeria and tumor cells. The purpose of the studies presented here was to determine the effects of benzene and benzene metabolites on macrophage functions and the ability of macrophages to be activated for functions which are important in host defense. Benzene had no effects on macrophage function or activation for any of the functions tested. Conversely, metabolites of benzene, catechol (CAT), hydroquinone (HQ), benzquinone (BQ), and 1,2,4-benzenetriol (BT) had potent and varied effects on macrophage function and activation. BQ inhibited the broadest range of functions including release of H2O2, Fc receptor-mediated phagocytosis, interferon gamma priming for tumor cell cytolysis, and bacterial lipopolysaccharide (LPS) triggering of cytolysis. BQ was also the most potent metabolite causing inhibition at lower concentrations than the other metabolites. HQ inhibited H2O2 release and priming for cytolysis and BT inhibited phagocytosis and priming for cytolysis. CAT only inhibited the release of H2O2. None of the compounds tested inhibited the induction of class II histocompatibility antigens on the cell surface. All of the effects measured occurred using concentrations of compounds which did not disrupt the cell integrity or inhibit general functions such as protein synthesis. Taken together these data suggest that benzene metabolites alter macrophage function through several mechanisms including inhibition of output enzymes and disruption of signal transduction systems.

The oxidation of tetrachloro-1,4-hydroquinone by microsomes and purified cytochrome P-450b. Implications for covalent binding to protein and involvement of reactive oxygen species

The enzymatic oxidation of tetrachloro-1,4-hydroquinone (1,4-TCHQ), resulting in covalent binding to protein of tetrachloro-1,4-benzoquinone (1,4-TCBQ), was investigated, with special attention to the involvement of cytochrome P-450 and reactive oxygen species. 1,4-TCBQ itself reacted very rapidly and extensively with protein (58% of the 10 nmol added to 2 mg of protein, in a 5-min incubation). Ascorbic acid and glutathione prevented covalent binding of 1,4-TCBQ to protein, both when added directly and when formed from 1,4-TCHQ by microsomes. In microsomal incubations as well as in a reconstituted system containing purified cytochrome P-450b, 1,4-TCHQ oxidation and subsequent protein binding was shown to be completely dependent on NADPH. The reaction was to a large extent, but not completely, dependent on oxygen (83% decrease in binding under anaerobic conditions). Inhibition of cytochrome P-450 by metyrapone, which is also known to block the P-450-mediated formation of reactive oxygen species, gave a 80% decrease in binding, while the addition of superoxide dismutase prevented 75% of the covalent binding, almost the same amount as found in anerobic incubations. A large part of the conversion of 1,4-TCHQ to 1,4-TCBQ is apparently not catalyzed by cytochrome P-450 itself, but is mediated by superoxide anion formed by this enzyme. The involvement of this radical anion is also demonstrated by microsomal incubations without NADPH but including the xantine/xantine oxidase superoxide anion generating system. These incubations resulted in a 1.6-fold binding as compared to the binding in incubations with NADPH but without xantine/xantine oxidase. 1,4-TCHQ was shown to stimulate the oxidase activity of microsomal cytochrome P-450. It is thus not unlikely that 1,4-TCHQ enhances its own microsomal oxidation.

Difference in metabolic profile of potassium canrenoate and spironolactone in the rat: mutagenic metabolites unique to potassium canrenoate

The metabolic fates of potassium canrenoate (PC) and spironolactone (SP) were compared for the rat in vivo and in vitro. Approximately 18% of an in vivo dose of SP was metabolized to canrenone (CAN) and related compounds in the rat. In vitro, 20-30% of SP was dethioacetylated to CAN and its metabolites by rat liver 9000 g supernatant (S9). Thus, the major route of SP metabolism is via pathways that retain the sulfur moiety in the molecule. PC was metabolized by rat hepatic S9 to 6 alpha, 7 alpha- and 6 beta, 7 beta-epoxy-CAN. The beta-epoxide was further metabolized to its 3 alpha- and 3 beta-hydroxy derivatives as well as its glutathione (GSH) conjugate. Both 3 alpha- and 3 beta-hydroxy-6 beta, 7 beta-epoxy-CAN were shown to be direct acting mutagens in the mouse lymphoma assay, whereas 6 alpha, 7 alpha- and 6 beta, 7 beta-epoxy-CAN were not. These mutagenic metabolites, their precursor epoxides and their GSH conjugates were not formed from SP under identical conditions. The above findings appear to be due to inhibition of metabolism of CAN formed from SP by SP and/or its S-containing metabolites, since the in vitro metabolism of PC by rat hepatic microsomes was appreciably reduced in the presence of SP. The hypothesized mechanism(s) for this inhibition is that SP and its S-containing metabolites specifically inhibit an isozyme of hepatic cytochrome P-450 or SP is a preferred substrate over PC/CAN for the metabolizing enzymes. Absence of the CAN epoxide pathway in the metabolism of SP provides a possible explanation for the observed differences in the toxicological profiles of the two compounds.

Increased risk of developing acute leukemia after employment as a painter

A case-control interview study of 125 adult patients with acute leukemia and 125 controls matched with respect to age (+/- four years), sex, and residence was carried out in central Sweden during the period from September 1980 to May 1983. Their history of organic solvent exposure is described. A significant overrisk of developing acute leukemia was found when comparison between patients and controls revealed a difference in the solvent exposure rate, which was significantly higher in patients than in controls, with an estimated odds ratio (OR) of 4.9, 95% CI (2.2 to 12.1). The most frequently exposed profession, painters, exhibit a relative risk of 13 (2.0 to 554). These results suggest that an etiologic relationship exists between organic solvent exposure and the development of acute leukemia in man.