A perspective on benzene leukemogenesis

Research development and trends of benzene-induced leukemia from 1990 to 2019-A bibliometric analysis

Benzene is an occupational and environmental toxicant, causing hematopoietic damage. Our study is aimed to extract the trend of benzene-induced leukemia (BIL) and qualitatively and quantitatively estimate research on it. Publications on BIL were identified from the Web of Science Core Collection (WoSCC). Microsoft Excel 2019 (Redmond, WA) and The CiteSpace 5.6.R5 software (Drexel University, Philadelphia, PA) were used to analyze the publication outcomes, countries, institutions, authors, keywords, and research frontiers. The overall 1152 publications were collected from 1990 to 2019 until November 6, 2020. Environ Health Persp had the highest number of articles published. The USA were the top country in terms of BIL. The Smith MT, Yin SN, Lan Q, and Hayes RB are both listed in the top 10 of co-cited authors, high contribution authors, and the authors of co-cited references. High IF articles account for a considerable proportion, among all the publications. Chinese institutions engaged in BIL and contributed a large part of articles. Exposure population, exposure dose, and exposure risk are the research hotspots in this field. The risk of benzene exposure on childhood leukemia is at issue, and the studies on attributable risk of benzene-induced leukemia are few. More early, sensitive, and specific epigenetic biomarkers of benzolism may be the leading research fields of benzene-induced leukemia in the next few years.

Genetic, epigenetic, and lineage-directed mechanisms in benzene-induced malignancies and hematotoxicity targeting hematopoietic stem cells niche

Benzene is a known hematotoxic and leukemogenic agent with hematopoietic stem cells (HSCs) niche being the potential target. Occupational and environmental exposure to benzene has been linked to the incidences of hematological disorders and malignancies. Previous studies have shown that benzene may act via multiple modes of action targeting HSCs niche, which include induction of chromosomal and micro RNA aberrations, leading to genetic and epigenetic modification of stem cells and probable carcinogenesis. However, understanding the mechanism linking benzene to the HSCs niche dysregulation is challenging due to complexity of its microenvironment. The niche is known to comprise of cell populations accounted for HSCs and their committed progenitors of lymphoid, erythroid, and myeloid lineages. Thus, it is fundamental to address novel approaches via lineage-directed strategy to elucidate precise mechanism involved in benzene-induced toxicity targeting HSCs and progenitors of different lineages. Here, we review the key genetic and epigenetic factors that mediate hematotoxicological effects by benzene and its metabolites in targeting HSCs niche. Overall, the use of combined genetic, epigenetic, and lineage-directed strategies targeting the HSCs niche is fundamental to uncover the key mechanisms in benzene-induced hematological disorders and malignancies.

DNA Damage by an essential enzyme: A delicate balance act on the tightrope

DNA topoisomerases are essential for DNA metabolic processes such as replication and transcription. Since DNA is double stranded, the unwinding needed for these processes results in DNA supercoiling and catenation of replicated molecules. Changing the topology of DNA molecules to relieve supercoiling or resolve catenanes requires that DNA be transiently cut. While topoisomerases carry out these processes in ways that minimize the likelihood of genome instability, there are several ways that topoisomerases may fail. Topoisomerases can be induced to fail by therapeutic small molecules such as by fluoroquinolones that target bacterial topoisomerases, or a variety of anti-cancer agents that target the eukaryotic enzymes. Increasingly, there have been a large number of agents and processes, including natural products and their metabolites, DNA damage, and the intrinsic properties of the enzymes that can lead to long-lasting DNA breaks that subsequently lead to genome instability, cancer, and other diseases. Understanding the processes that can interfere with topoisomerases and how cells respond when topoisomerases fail will be important in minimizing the consequences when enzymes need to transiently interfere with DNA integrity.

Exposure and Risk Assessment with Respect to Contaminated Soil: Significance of Biomarkers and Bioavailability

The evaluation of health risk from chemical exposure is evolving in concept and practice. The ability to sensitively detect levels of chemicals in the environment has served as the traditional foundation for determining exposure levels and consequent health risks. More recently, however, other parameters have been constructed to probe the pathway between environmental levels of a chemical and the biological effects of subsequent exposure. Among these, two that are discussed in this paper are bioavailability and biomarker determinations. Chemicals in the environment often are associated with a medium such as airborne particulate, water, or soil. The interaction between the chemical and its medium is dependent on the physicochemical properties of the system. In some cases, such as 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD) in soil, the chemical becomes partially and irreversibly bound to the medium. Animalingestion studies of TCDD-contaminated soil suggest that some of the TCDD remains bound to the soil and does not cross the gastrointestinal barrier during digestion, and therefore only a fraction of the TCDD enters the blood and becomes bioavailable. The characterization of bioavailability provides for more accurate exposure assessment. Biomarker information potentially can validate exposure assessment information from bioavailability studies, elucidate specific biological effects from chemical exposure, and investigate genetic susceptibility issues that may increase the likelihood that an individual or population will experience increased health risks. Benzene-induced chromosome damage is discussed as an example of a significant biomarker that has demonstrated the potential for providing information useful for accurately prediction health risk.

Depurinating estrogen-DNA adducts, generators of cancer initiation: their minimization leads to cancer prevention

Estrogens can initiate cancer by reacting with DNA. Specific metabolites of endogenous estrogens, the catechol estrogen-3,4-quinones, react with DNA to form depurinating estrogen-DNA adducts. Loss of these adducts leaves apurinic sites in the DNA, generating mutations that can lead to the initiation of cancer. A variety of endogenous and exogenous factors can disrupt estrogen homeostasis, which is the normal balance between estrogen activating and protective enzymes. In fact, if estrogen metabolism becomes unbalanced and generates excessive catechol estrogen 3,4-quinones, formation of depurinating estrogen-DNA adducts increases and the risk of initiating cancer is greater. The levels of depurinating estrogen-DNA adducts are high in women diagnosed with breast cancer and those at high risk for the disease. High levels of depurinating estrogen-DNA adducts before the presence of breast cancer indicates that adduct formation is a critical factor in breast cancer initiation. Women with thyroid or ovarian cancer also have high levels of estrogen-DNA adducts, as do men with prostate cancer or non-Hodgkin lymphoma. Depurinating estrogen-DNA adducts are initiators of many prevalent types of human cancer. These findings and other discoveries led to the recognition that reducing the levels of estrogen-DNA adducts could prevent the initiation of human cancer. The dietary supplements N-acetylcysteine and resveratrol inhibit formation of estrogen-DNA adducts in cultured human breast cells and in women. These results suggest that the two supplements offer an approach to reducing the risk of developing various prevalent types of human cancer. Graphical abstract Major metabolic pathway in cancer initiation by estrogens.

The molecular etiology and prevention of estrogen-initiated cancers: Ockham's Razor: Pluralitas non est ponenda sine necessitate. Plurality should not be posited without necessity

Elucidation of estrogen carcinogenesis required a few fundamental discoveries made by studying the mechanism of carcinogenesis of polycyclic aromatic hydrocarbons (PAH). The two major mechanisms of metabolic activation of PAH involve formation of radical cations and diol epoxides as ultimate carcinogenic metabolites. These intermediates react with DNA to yield two types of adducts: stable adducts that remain in DNA unless removed by repair and depurinating adducts that are lost from DNA by cleavage of the glycosyl bond between the purine base and deoxyribose. The potent carcinogenic PAH benzo[a]pyrene, dibenzo[a,l]pyrene, 7,12-dimethylbenz[a]anthracene and 3-methylcholanthrene predominantly form depurinating DNA adducts, leaving apurinic sites in the DNA that generate cancer-initiating mutations. This was discovered by correlation between the depurinating adducts formed in mouse skin by treatment with benzo[a]pyrene, dibenzo[a,l]pyrene or 7,12-dimethylbenz[a]anthracene and the site of mutations in the Harvey-ras oncogene in mouse skin papillomas initiated by one of these PAH. By applying some of these fundamental discoveries in PAH studies to estrogen carcinogenesis, the natural estrogens estrone (E1) and estradiol (E2) were found to be mutagenic and carcinogenic through formation of the depurinating estrogen-DNA adducts 4-OHE1(E2)-1-N3Ade and 4-OHE1(E2)-1-N7Gua. These adducts are generated by reaction of catechol estrogen quinones with DNA, analogously to the DNA adducts obtained from the catechol quinones of benzene, naphthalene, and the synthetic estrogens diethylstilbestrol and hexestrol. This is a weak mechanism of cancer initiation. Normally, estrogen metabolism is balanced and few estrogen-DNA adducts are formed. When estrogen metabolism becomes unbalanced, more catechol estrogen quinones are generated, resulting in higher levels of estrogen-DNA adducts, which can be used as biomarkers of unbalanced estrogen metabolism and, thus, cancer risk. The ratio of estrogen-DNA adducts to estrogen metabolites and conjugates has repeatedly been found to be significantly higher in women at high risk for breast cancer, compared to women at normal risk. These results indicate that formation of estrogen-DNA adducts is a critical factor in the etiology of breast cancer. Significantly higher adduct ratios have been observed in women with breast, thyroid or ovarian cancer. In the women with ovarian cancer, single nucleotide polymorphisms in the genes for two enzymes involved in estrogen metabolism indicate risk for ovarian cancer. When polymorphisms produce high activity cytochrome P450 1B1, an activating enzyme, and low activity catechol-O-methyltransferase, a protective enzyme, in the same woman, she is almost six times more likely to have ovarian cancer. These results indicate that formation of estrogen-DNA adducts is a critical factor in the etiology of ovarian cancer. Significantly higher ratios of estrogen-DNA adducts to estrogen metabolites and conjugates have also been observed in men with prostate cancer or non-Hodgkin lymphoma, compared to healthy men without cancer. These results also support a critical role of estrogen-DNA adducts in the initiation of cancer. Starting from the perspective that unbalanced estrogen metabolism can lead to increased formation of catechol estrogen quinones, their reaction with DNA to form adducts, and generation of cancer-initiating mutations, inhibition of estrogen-DNA adduct formation would be an effective approach to preventing a variety of human cancers. The dietary supplements resveratrol and N-acetylcysteine can act as preventing cancer agents by keeping estrogen metabolism balanced. These two compounds can reduce the formation of catechol estrogen quinones and/or their reaction with DNA. Therefore, resveratrol and N-acetylcysteine provide a widely applicable, inexpensive approach to preventing many of the prevalent types of human cancer.

Hematological Evidence of Occupational Exposure to Chemicals and Other Factors among Auto-Repair Workers in Rawalpindi, Pakistan

Objectives

Occupational exposure to aromatic solvents causes many serious health hazards to workers, especially if an ambient environment increases the exposure during routine working hours. This study was conducted on two related groups, i.e., automobile mechanics (MCs) and automobile spray painters (PNs), with an effort to analyze effects of chemical exposure on hematological parameters, keeping a focus on environmental parameters and workers’ personal behavioral characteristics that could be held responsible for increasing exposure risk.

Methods

A preliminary survey of various chemicals used in these places was done, and 78 blood samples were collected from three groups (control, n = 24; mechanics, n = 25; painters, n = 29). Demographic features of workers were recorded through a short questionnaire.

Results

Results showed that mean red blood cell (RBC) count was lower both in MCs [t(51) = 2.38, p < 0.021, r = 0.32] and in PNs [t(47) = 2.12, p < 0.03, r = 0.29], whereas mean hemoglobin (Hb) was significantly lower in MCs [t(51) = 2.5, p = 0.017, r = 0.33]. Combined data for exposed groups for smokers (SMs) versus nonsmokers (NSs) showed that SMs had a significantly lower number (RBC count: t(52) = 2.28, p < 0.027, r = 0.25; Hb count: t(52) = 2.71, p < 0.009, r = 0.30] of these parameters than NSs, even compared to the control group. Moreover, logistic regression results showed that smoking is a significant predictor of reduction in RBC and Hb counts, besides occupational exposure and work experience to a little extent among exposed workers. Mean white blood cell count [t(47) = 2.63, p < 0.01, r=0.35], mean corpuscle volume [t(47)= –2.82, p = 0.007, r = 0.29], and packed cell volume [t(47)= –2.28, p = 0.027, r = 31] were higher exclusively in painters, which could be related to exposure to benzene in addition to isocyanate.

Conclusion

It appeared that workplace exposure may be complex due to interaction of multiple factors and PNs face much more exposure to isocyanate and aromatic solvents than MCs, which had significant effects on their hematopoiesis. Smoking enhances exposure risk manifolds, and among MCs it showed combined effects along with occupational exposure. There is a need to create awareness among these workers to adopt self-safety measures during routine tasks and also of a separate study to elucidate actual occupational exposure among them, eliminating confounding factors.

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.

Occupational exposure to aromatic hydrocarbons and polycyclic aromatic hydrocarbons at a coke plant

OBJECTIVES

The objective of this study was to assess the external exposure to aromatic hydrocarbons (AHs) and polycyclic aromatic hydrocarbons (PAHs) of coke-oven workers and by-product workers at a coke plant in Poland.

METHODS

The content of benzene, toluene, xylene, and naphthalene in a gaseous phase and the content of dibenzo[a,h]anthracene, benz[a]anthracene, anthracene, benzo[a]pyrene, benzo[b]fluoranthene, benzo[k]fluoranthene, benz[ghi]perylene, chrysene, and indeno[1,2,3-c,d]pyrene in a particulate phase of coke plant workers were measured in the workers mentioned above. A toxic equivalency factor BaP(eq) was used to estimate human health risk associated with respiratory exposure to PAHs.

RESULTS

Time-weighted values of the exposure to AHs in the coke plant were as follows: benzene (range 0.01-2.71 mg m(-3)), toluene (0.01-1.73 mg m(-3)), xylene (0.01-0.78 mg m(-3)), naphthalene (6.0-6079 μg m(-3)), and the concentrations of hydrocarbons did not exceed the exposure limits. The results for particle-bound PAHs were equal to 1.96 μg m(-3) for B(a)P, 0.73 μg m(-3) for DBA, 3.23 μg m(-3) for BaA, 4.35 μg m(-3) for BbF, 3.02 μg m(-3) for BkF, 4.54 μg m(-3) for IND, 4.32 μg m(-3) for CHR, and 0.73 μg m(-3) for Ant. The results of personal air measurements (median values of the sum of nine carcinogenic PAHs) were 2.115 μg m(-3) (coke-oven workers, n = 207), 0.326 μg m(-3) (coke by-product workers, n = 33), and 0.653 μg m(-3) (total area workers, n = 38). The benzo[a]pyrene equivalent concentrations (BaP(eq)) of 10 PAHs were 1.33, 0.183, and 0.284 μg m(-3), respectively.

CONCLUSIONS

We found out that coke plant workers are simultaneously exposed to a mixture of aromatic and polycyclic hydrocarbons present in the breathing zone air. Exposure levels are significantly influenced by job categories. Coke by-product workers are significantly more exposed to benzene, toluene, and xylene and less to PAHs. Coke-oven workers are mainly exposed to PAHs. Coke-oven workplaces (top side, coke side, and push side) are characterized by higher carcinogenic risk than other coke plant workplaces.

United States Voluntary Children's Chemical Evaluation Program (VCCEP) risk assessment for children exposed to benzene

As part of the Voluntary Children's Chemical Evaluation Program (VCCEP) program, a risk assessment was performed to evaluate the risks to children from environmental benzene exposures. This paper summarizes this risk assessment. Risk was characterized using two distinct methods: USEPA's default type of risk assessment, which used the Reference Dose (RfD) and Cancer Slope Factor (CSF) to characterize non-cancer and cancer risks, as well as a Margin of Safety (MOS) approach that utilized a point of departure (POD). The exposures for most scenarios evaluated in this VCCEP risk assessment are lower than both the cancer and non-cancer PODs by several orders of magnitude, indicating a large MOS and corresponding low potential for toxicity at these exposures. The highest benzene exposures likely experienced by children, associated with the lowest MOS, are from cigarette smoke. In addition, the potential for age-related differences in the sensitivity towards benzene-induced toxicity was investigated. In general, this risk assessment does not indicate that children are likely to be at a elevated risk of AML or hematopoietic toxicity associated with environmental exposures to benzene.

Assessment of the impact of the vehicular traffic on BTEX concentration in ring roads in urban areas of Bari (Italy)

A BTEX monitoring campaign, consisting of two weekly periods, was carried out in Bari, south-eastern Italy, in order to evaluate the impact of the vehicular traffic on the air quality at the main access roads of the city. Twenty-one sampling sites were selected: the pollution produced by the traffic in the vicinity of all exits from the ring road and some access roads to the city, those with higher traffic density, were monitored. Contemporarily the main meteorological parameters (ambient temperature, wind, atmospheric pressure and natural radioactivity) were investigated. It was found that in the same traffic conditions, barriers, buildings and local meteorological conditions can have important effects on the atmospheric dispersion of pollutants. This situation is more critical in downtown where narrow roads and high buildings avoid an efficient dispersion producing higher levels of BTEX. High spatial resolution monitoring allowed both detecting the most critical areas of the city with high precision and obtaining information on the mean level of pollution, meaning air quality standard of the city. The same concentration pattern and the correlation among BTEX levels in all sites confirmed the presence of a single source, the vehicular traffic, having a strong impact on air quality.

Benzene and dopamine catechol quinones could initiate cancer or neurogenic disease

Catechol quinones of estrogens react with DNA by 1,4-Michael addition to form depurinating N3Ade and N7Gua adducts. Loss of these adducts from DNA creates apurinic sites that can generate mutations leading to cancer initiation. We compared the reactions of the catechol quinones of the leukemogenic benzene (CAT-Q) and N-acetyldopamine (NADA-Q) with 2'-deoxyguanosine (dG) or DNA. NADA was used to prevent intramolecular cyclization of dopamine quinone. Reaction of CAT-Q or NADA-Q with dG at pH 4 afforded CAT-4-N7dG or NADA-6-N7dG, which lost deoxyribose with a half-life of 3 h to form CAT-4-N7Gua or 4 h to form NADA-6-N7Gua. When CAT-Q or NADA-Q was reacted with DNA, N3Ade adducts were formed and lost from DNA instantaneously, whereas N7Gua adducts were lost over several hours. The maximum yield of adducts in the reaction of CAT-Q or NADA-Q with DNA at pH 4 to 7 was at pH 4. When tyrosinase-activated CAT or NADA was reacted with DNA at pH 5 to 8, adduct levels were much higher (10- to 15-fold), and the highest yield was at pH 5. Reaction of catechol quinones of natural and synthetic estrogens, benzene, naphthalene, and dopamine with DNA to form depurinating adducts is a common feature that may lead to initiation of cancer or neurodegenerative disease.

ATSDR evaluation of health effects of benzene and relevance to public health

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.

In silico studies with human DNA topoisomerase-II alpha to unravel the mechanism of in vitro genotoxicity of benzene and its metabolites

Exposure of humans to benzene present in environment may lead to adverse chronic effects-even at the genetic level. However, the mechanism of its genotoxicity is not well understood. In the present study, in vitro genotoxicity of benzene (BZ) and its major metabolites [p-benzoquinone (BQ), hydroquinone (HQ), catechol (CT), 1,2,4-benzenetriol (BT) and trans-trans muconic acid (MA)] at concentrations 0.5-50 microM, was assessed in Chinese hamster ovary (CHO) cells employing the alkaline Comet assay, cytokinesis blocked micronucleus (CBMN) assay, flow cytometric analysis of micronucleus (flow MN) and chromosome aberration (CA) test. The data revealed significant (P<0.05) concentration-dependent response in all end points. HQ was found to be the most potent DNA damaging metabolite in the Comet assay followed by BQ>BT>CT>BZ>MA. Both CBMN and flow MN assays revealed a good correlation in their results, where BQ and MA exhibited maximum and minimum micronucleus induction respectively. Significant chromosomal aberrations were induced mainly by BQ, BT and HQ, with moderate response shown by CT and BZ and least by MA. The results demonstrated the utility of sensitive techniques like Comet assay and flow cytometry for determination of MN, to quantify in vitro genotoxicity at low levels and also suggested that partly non-repaired DNA damage could cause adverse health effects in human population exposed to benzene. In silico studies using different endpoints of genotoxicity and molecular docking studies with human topoisomerase-II alpha, a major DNA repair enzyme were also conducted. These corroborated the results obtained from the in vitro data, pointing to a direct relationship of the observed genotoxicity with the structural properties and various interactions of metabolites with the enzyme. This comprehensive study demonstrated that genotoxicity of benzene in mammalian cells is mainly due to the inhibition of topoisomerase by the metabolites.

DNA topoisomerase II, genotoxicity, and cancer

Type II topoisomerases are ubiquitous enzymes that play essential roles in a number of fundamental DNA processes. They regulate DNA under- and overwinding, and resolve knots and tangles in the genetic material by passing an intact double helix through a transient double-stranded break that they generate in a separate segment of DNA. Because type II topoisomerases generate DNA strand breaks as a requisite intermediate in their catalytic cycle, they have the potential to fragment the genome every time they function. Thus, while these enzymes are essential to the survival of proliferating cells, they also have significant genotoxic effects. This latter aspect of type II topoisomerase has been exploited for the development of several classes of anticancer drugs that are widely employed for the clinical treatment of human malignancies. However, considerable evidence indicates that these enzymes also trigger specific leukemic chromosomal translocations. In light of the impact, both positive and negative, of type II topoisomerases on human cells, it is important to understand how these enzymes function and how their actions can destabilize the genome. This article discusses both aspects of human type II topoisomerases.

Catechol Quinones of Estrogens in the Initiation of Breast, Prostate, and Other Human Cancers: Keynote Lecture

Estrogens can be converted to electrophilic metabolites, particularly the catechol estrogen-3,4-quinones, estrone(estradiol)-3,4-quinone [E(1)(E(2))-3,4-Q], which react with DNA to form depurinating adducts. These adducts are released from DNA to generate apurinic sites. Error-prone repair of this damage leads to the mutations that initiate breast, prostate, and other types of cancer. The reaction of E(1)(E(2))-3,4-Q with DNA forms the depurinating adducts 4-hydroxyE(1)(E(2))-1-N3adenine [4-OHE(1)(E(2))-1-N3Ade] and 4-OHE(1)(E(2))-1-N7guanine(Gua). These two adducts constitute >99% of the total DNA adducts formed. The E(1)(E(2))-2,3-Q forms small amounts of the depurinating 2-OHE(1)(E(2))-6-N3Ade adducts. Reaction of the quinones with DNA occurs more abundantly when estrogen metabolism is unbalanced. Such an imbalance is the result of overexpression of estrogen-activating enzymes and/or deficient expression of deactivating (protective) enzymes. Excessive formation of E(1)(E(2))-3,4-Q is the result of this imbalance. Oxidation of catechols to semiquinones and quinones is a mechanism of tumor initiation not only for endogenous estrogens, but also for synthetic estrogens such as hexestrol and diethylstilbestrol, a human carcinogen. This mechanism is also involved in the initiation of leukemia by benzene, rat olfactory tumors by naphthalene, and neurodegenerative diseases such as Parkinson's disease by dopamine. In fact, dopamine quinone reacts with DNA similarly to the E(1)(E(2))-3,4-Q, forming analogous depurinating N3Ade and N7Gua adducts. The depurinating adducts that migrate from cells and can be found in body fluids can also serve as biomarkers of cancer risk. In fact, a higher level of estrogen-DNA adducts has been found in the urine of men with prostate cancer and in women with breast cancer compared to healthy controls. This unifying mechanism of the origin of cancer and other diseases suggests preventive strategies based on the level of depurinating DNA adducts that generate the first critical step in the initiation of diseases.

A Class of Benzenoid Chemicals Suppresses Apoptosis in C. elegans

Benzene is a human carcinogen that might act through both genotoxic and nongenotoxic mechanisms to promote tumorigenesis. The genotoxic effects of benzene are well established, however, its potential nongenotoxic roles in carcinogenesis are poorly understood. We find that benzene suppresses somatic apoptosis in C. elegans; this suggests a potential nongenotoxic mechanism by which this chemical might promote tumorigenesis. We find that two other benzenoid chemicals, biphenyl and toluene, also inhibit apoptosis in C. elegans. Notably, these chemicals are suspected carcinogens in mammals; this suggests that a subclass of benzenoid chemicals might promote tumorigenesis by suppressing apoptosis. A benzene metabolite, 1,4-benzoquinone, can directly inhibit the activity of caspase-3; this suggests a general molecular mechanism by which benzenoid chemicals might suppress apoptosis. These findings suggest that C. elegans is an excellent alternative animal model for studying the antiapoptotic activity of tumor-promoting chemicals and for identifying in vivo targets of these chemicals.

Formaldehyde as a potential human leukemogen: an assessment of biological plausibility

The International Agency for Research on Cancer (IARC, 2004) recently reevaluated the epidemiological data on formaldehyde and concluded that there was "strong but not sufficient evidence for a causal association between leukaemia and occupational exposure to formaldehyde." This conclusion was tempered since a mechanism for leukemia induction could not be identified. Chemically induced leukemia is a well-studied phenomenon with benzene and a number of cancer chemotherapeutic drugs recognized as capable of causing this effect. Abundant in vitro and in vivo data in animals and humans demonstrate that exposure to sufficient doses of these recognized leukemogens can initiate a cascade of events leading to hematopoietic toxicity and the subsequent development of leukemia. This review addresses the biological plausibility that formaldehyde might be capable of causing any type of leukemia by providing a broad overview of the scientific data that must be considered in order to support or refute a conclusion that a particular substance might be leukemogenic. Data on benzene and selected chemotherapeutic cancer drugs are used as examples and are briefly summarized to demonstrate the similar biological events thought to result in leukemogenesis. These data are compared and contrasted with the available data on formaldehyde in order to judge whether they fulfill the criteria of biological plausibility that formaldehyde would be capable of inducing leukemia as suggested by the epidemiological data. Based on the epidemiological data, it is reasonable to expect that if formaldehyde was capable of inducing leukemia, in vivo and in vitro data would offer supporting evidence for biological plausibility. In particular, there is (1) no evidence to suggest that formaldehyde reaches any target organ beyond the site of administration including the bone marrow, (2) no indication that formaldehyde is toxic to the bone marrow/hematopoietic system in in vivo or in vitro studies, and (3) no credible evidence that formaldehyde induces leukemia in experimental animals. As discussed in this review, based on the key biological events that occur in the process of chemically induced leukemia, there is inadequate biological evidence currently available to corroborate existing weak epidemiological associations. This provides an insufficient database to conclude that there is a causal relationship for formaldehyde and leukemia risk.

Solvent and substituent effects on spectroscopical changes of some diazoaminobenzene derivatives

A series of diazoaminobenzene derivatives (seven) in which the substituents have a wide range of electronic characters are set out to understand the involvement of the substituent identity in controlling the changes in their electronic absorption spectra. The interactions between the diazoamino group and the different groups account for some spectral shifts. The UV-vis spectrum of each compound is measured in several solvents with wide variations of solvent polarity parameters to examine the role of the chemistry of the solvent in these spectroscopical changes. The electronic transitions are assigned and the solvent induced spectral shifts are analyzed in relation to the different solute-solvent interaction mechanisms using computational chemistry. The regression analysis is applied for correlating the different parameters. The results help to assign the solute-solvent interactions and the solvatochromic potential of the investigated compounds. It is concluded that the electronic character of the substituent and the chemical nature of the solvent are the major factors for the observed solvatochromism.

Effects of benzene metabolites on DNA cleavage mediated by human topoisomerase II alpha: 1,4-hydroquinone is a topoisomerase II poison

Although benzene induces leukemias in humans, the compound is not believed to generate chromosomal damage directly. Rather, benzene is thought to act through a series of phenolic- and quinone-based metabolites, especially 1,4-benzoquinone. A recent study found that 1,4-benzoquinone is a potent topoisomerase II poison in vitro and in cultured human cells [Lindsey et al. (2004) Biochemistry 43, 7363-7374]. Because benzene is metabolized to multiple compounds in addition to 1,4-benzoquinone, we determined the effects of several phenolic metabolites, including catechol, 1,2,4-benzenetriol, 1,4-hydroquinone, 2,2'-biphenol, and 4,4'-biphenol, on the DNA cleavage activity of human topoisomerase II alpha. Only 1,4-hydroquinone generated substantial levels of topoisomerase II-mediated DNA scission. DNA cleavage with this compound approached levels observed with 1,4-benzoquinone (approximately 5- vs 8-fold) but required a considerably higher concentration (approximately 250 vs 25 microM). 1,4-Hydroquinone is a precursor to 1,4-benzoquinone in the body and can be activated to the quinone by redox cycling. It is not known whether the effects of 1,4-hydroquinone on human topoisomerase II alpha reflect a lower reactivity of the hydroquinone or a low level of activation to the quinone. The high concentration of 1,4-hydroquinone required to increase enzyme-mediated DNA cleavage is consistent with either explanation. 1,4-Hydroquinone displayed attributes against topoisomerase II alpha, including DNA cleavage specificity, that were similar to those of 1,4-benzoquinone. However, 1,4-hydroquinone consistently inhibited DNA ligation to a greater extent than 1,4-benzoquinone. This latter result implies that the hydroquinone may display (at least in part) independent activity against topoisomerase II alpha. The present findings are consistent with the hypothesis that topoisomerase II alpha plays a role in the initiation of specific types of leukemia that are induced by benzene and its metabolites.

Differential induction of micronuclei in peripheral lymphocytes and exfoliated urothelial cells of workers exposed to 4,4'-methylenebis-(2-chloroaniline) (MOCA) and bitumen fumes

Cytogenetic end-points used to estimate risk of genotoxic events in workers include the measurement of micronuclei (MN) in exfoliated cells, lymphocytes, and other tissues. Micronuclei are chromatin-containing bodies outside the cell nucleus resulting from contaminant-induced DNA damage. A review of 71 reports of human genotoxic responses to chemical or physical agents published between 1999 and 2001 revealed that 14% of such studies measured genotoxicity endpoints in specific target tissues relevant to the site of disease for the agent examined; 18% used endpoints in surrogate or non-target tissues but considered the relations between endpoints in surrogate and disease target tissues, and 68% measured genotoxicity endpoints in accessible tissues without reference to specific targets for disease. Methylenebis-(2-chloroaniline) (MOCA), used in polyurethane manufacture, is a suspected bladder carcinogen. Bitumen, used in road surfacing, contains skin and lung carcinogens. In this study, we aimed to compare genotoxicity in urothelial cells and in lymphocytes of workers exposed to these materials. Twelve men employed in polyurethane manufacture, twelve bitumen road layers, and eighteen hospital stores personnel (controls) were recruited and all provided blood and urine samples on the same day. Blood cultures were prepared using a cytochalasin B-block method. Exfoliated urothelial cells were collected from urine and stained for light microscopy. The number of MN in urothelial cells was higher in MOCA-exposed (14.27 +/- 0.56 MN/1000, 9.69 +/- 0.32 MN cells/1000) than in bitumen exposed workers (11.99 +/- 0.65 MN/1000, 8.66 +/- 0.46 MN cells/1000) or in control subjects (6.88 +/- 0.18 MN/1000, 5.17 +/- 0.11 MN cells/1000). Conversely, in lymphocytes, MN were higher in bitumen-exposed (16.24 +/- 0.63 MN/1000, 10.65 +/- 0.24 MN cells/1000) than in MOCA-exposed workers (13.25 +/- 0.48 MN/1000, 8.54 +/- 0.14 MN cells/1000) or in control subjects (9.24 +/- 0.29 MN/ 1000, 5.93 +/- 0.13 MN cells/1000). The results of this study suggest that genotoxins can cause different rates of micronuclei formation in different tissues. Thus, the sensitivity and relevance to cancer risk may be greater if the tissues selected for genotoxicity studies reflect the target tissue for the chemicals concerned.

Do children have increased susceptibility for developing secondary acute myelogenous leukemia?

This study was undertaken to evaluate the effects of age on a child's susceptibility to developing leukemia following exposure to known leukemogenic agents. The clinical literature describing the risk of developing acute myelogenous leukemia (AML) following treatment with alkylating agents or topoisomerase reactive drugs (known leukemogens) was used as a basis for this investigation. Based on this preliminary assessment, the age of the child does not appear to be an independent variable for risk following treatment with either class of drug. Although the number of studies and cases was very small, the available scientific and medical literature does not support the hypothesis that children will necessarily have an altered susceptibility or increased risk of developing chemotherapy-induced AML.

Stimulation of topoisomerase II-mediated DNA cleavage by benzene metabolites

Benzene is a human carcinogen that induces hematopoietic malignancies. It is believed that benzene does not initiate leukemias directly, but rather generates DNA damage through a series of phenolic and quinone-based metabolites, especially 1,4-benzoquinone. Since the DNA damage induced by 1,4-benzoquinone is consistent with that of topoisomerase II-targeted drugs, it has been proposed that the compound initiates specific types of leukemia by acting as a topoisomerase II poison. This hypothesis, however, was not supported by initial in vitro studies. While 1,4-benzoquinone inhibited topoisomerase II catalysis, increases in enzyme-mediated DNA cleavage were not observed. Because of the potential involvement of topoisomerase II in benzene-induced leukemias, we re-examined the effects of benzene metabolites (including 1,4-benzoquinone, 1,4-hydroquinone, catechol, 1,2,4-benzenetriol, 2,2'-biphenol, and 4,4'-biphenol) on DNA cleavage mediated by human topoisomerase IIalpha. In contrast to previous reports, we found that 1,4-benzoquinone was a strong topoisomerase II poison and was more potent in vitro than the anticancer drug etoposide. Other metabolites displayed considerably less activity. DNA cleavage enhancement by 1,4-benzoquinone was unseen in previous studies due to the presence of reducing agents and the incubation of 1,4-benzoquinone with the enzyme prior to the addition of DNA. Unlike anticancer drugs such as etoposide that interact with topoisomerase IIalpha in a noncovalent manner, the actions of 1,4-benzoquinone appear to involve a covalent attachment to the enzyme. Finally, 1,4-benzoquinone stimulated DNA cleavage by topoisomerase IIalpha in cultured human cells. These findings are consistent with the hypothesis that topoisomerase IIalpha plays a role in the initiation of some benzene-induced leukemias.

The impact of reduction in the benzene limit value in gasoline on airborne benzene, toluene and xylenes levels

Background benzene, toluene, xylenes (BTX) average concentrations have been measured over the urban agglomeration of Toulouse, France, during both springtime and summer periods of 1999 and 2001. The benzene average amount over the two Toulouse campaigns in 1999 is equal to 2.2 microg/m(3), very close to the French air quality standard and well under the average value of 5 microg/m(3) recommended by European Economic Community countries, recognising that those regulations are given for a whole year. BTX pollution over Toulouse has, in particular, been produced by motor vehicle exhaust gases. For the study conducted during the same periods of 2001, benzene concentrations were within the French quality value in the whole area. This is because the benzene limit value contained in gasoline went from 5% to 1% since 2000 January 1. It will be important to measure benzene over annual periods in order to know its exact values over such a period and to observe its potential seasonal variations.

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.

Stimulation of endothelial IL-8 (eIL-8) production and apoptosis by phenolic metabolites of benzene in HL-60 cells and human bone marrow endothelial cells

Benzene toxicity is considered to be elicited by its metabolites and phenolic metabolites of benzene are known to induce apoptosis in leukemia cells in culture and in human bone marrow progenitor cells. One potential mechanism of apoptosis induced by benzene metabolites that has not been examined is the production of pro-apoptotic cytokines such as endothelial IL-8 from endothelial cells in bone marrow stroma. In this study, we utilized HL-60 cells which are known to produce the endothelial form of IL-8 (elL-8) and human bone marrow endothelial cells (HBMEC) as model systems. Hydroquinone (HQ), Catechol (Cat) and benzenetriol (BT) all induced eIL-8 production and apoptosis in HL-60 cells. HQ induced a marked 50-70-fold stimulation of eIL-8 levels and HL-60 cells were shown to have the eIL-8 receptor, CXCR I thus enabling an autocrine pathway of apoptosis. However, treatment with recombinant elL-8 failed to induce apoptosis in HL-60 cells as previously reported and antibodies to either IL-8 or CXCRI did not significantly abrogate benzene metabolite-induced apoptosis. HQ and Cat but not BT also induced stimulation of elL-8 production in HBMEC. These data demonstrate that although metabolites of benzene induce marked stimulation of eIL-8, this is unlikely to be responsible for apoptosis induced in HL-60 cells. Our data also demonstrates that phenolic metabolites of benzene stimulate the production of eIL-8 from HBMEC suggesting that higher levels of endothelial-derived cytokines may occur in bone marrow after benzene exposure.

Stimulation of endothelial IL-8 (eIL-8) production and apoptosis by phenolic metabolites of benzene in HL-60 cells and human bone marrow endothelial cells

Benzene toxicity is considered to be elicited by its metabolites and phenolic metabolites of benzene are known to induce apoptosis in leukemia cells in culture and in human bone marrow progenitor cells. One potential mechanism of apoptosis induced by benzene metabolites that has not been examined is the production of pro-apoptotic cytokines such as endothelial IL-8 from endothelial cells in bone marrow stroma. In this study, we utilized HL-60 cells which are known to produce the endothelial form of IL-8 (eIL-8) and human bone marrow endothelial cells (HBMEC) as model systems. Hydroquinone (HQ), Catechol (Cat) and benzenetriol (BT) all induced eIL-8 production and apoptosis in HL-60 cells. HQ induced a marked 50-70 fold stimulation of eIL-8 levels and HL-60 cells were shown to have the eIL-8 receptor, CXCR1 thus enabling an autocrine pathway of apoptosis. However, treatment with recombinant eIL-8 failed to induce apoptosis in HL-60 cells as previously reported and antibodies to either IL-8 or CXCR1 did not significantly abrogate benzene metabolite-induced apoptosis. HQ and Cat but not BT also induced stimulation of eIL-8 production in HBMEC. These data demonstrate that although metabolites of benzene induce marked stimulation of eIL-8, this is unlikely to be responsible for apoptosis induced in HL-60 cells. Our data also demonstrates that phenolic metabolites of benzene stimulate the production of eIL-8 from HBMEC suggesting that higher levels of endothelial-derived cytokines may occur in bone marrow after benzene exposure.

Genotoxicity of benzene and its metabolites

The potential role of genotoxicity in human leukemias associated with benzene (BZ) exposures was investigated by a systematic review of over 1400 genotoxicity test results for BZ and its metabolites. Studies of rodents exposed to radiolabeled BZ found a low level of radiolabel in isolated DNA with no preferential binding in target tissues of neoplasia. Adducts were not identified by 32P-postlabeling (equivalent to a covalent binding index <0.002) under the dosage conditions producing neoplasia in the rodent bioassays, and this method would have detected adducts at 1/10,000th the levels reported in the DNA-binding studies. Adducts were detected by 32P-postlabeling in vitro and following high acute BZ doses in vivo, but levels were about 100-fold less than those found by DNA binding. These findings suggest that DNA-adduct formation may not be a significant mechanism for BZ-induced neoplasia in rodents. The evaluation of other genotoxicity test results revealed that BZ and its metabolites did not produce reverse mutations in Salmonella typhimurium but were clastogenic and aneugenic, producing micronuclei, chromosomal aberrations, sister chromatid exchanges and DNA strand breaks. Rodent and human data were compared, and BZ genotoxicity results in both were similar for the available tests. Also, the biotransformation of BZ was qualitatively similar in rodents, humans and non-human primates, further indicating that rodent and human genotoxicity data were compatible. The genotoxicity test results for BZ and its metabolites were the most similar to those of topoisomerase II inhibitors and provided less support for proposed mechanisms involving DNA reactivity, mitotic spindle poisoning or oxidative DNA damage as genotoxic mechanisms; all of which have been demonstrated experimentally for BZ or its metabolites. Studies of the chromosomal translocations found in BZ-exposed persons and secondary human leukemias produced by topoisomerase II inhibitors provide some additional support for this mechanism being potentially operative in BZ-induced leukemia.

1,4-Benzoquinone Is a Topoisomerase II Poison†

Benzene is a human carcinogen that induces hematopoietic malignancies. It is believed that benzene does not initiate leukemias directly, but rather generates DNA damage through a series of phenolic metabolites, especially 1,4-benzoquinone. The cellular consequences of 1,4-benzoquinone are consistent with those of topoisomerase II-targeted drugs. Therefore, it has been proposed that the compound initiates specific leukemias by acting as a topoisomerase II poison. This hypothesis, however, has not been supported by in vitro studies. While 1,4-benzoquinone has been shown to inhibit topoisomerase II catalysis, increases in enzyme-mediated DNA cleavage have not been reported. Because of the potential involvement of topoisomerase II in benzene-induced leukemias, we re-examined the effects of the compound on DNA cleavage mediated by human topoisomerase IIalpha. In contrast to previous reports, we found that 1,4-benzoquinone was a strong topoisomerase II poison and was more potent in vitro than the anticancer drug etoposide. DNA cleavage enhancement probably was unseen in previous studies due to the presence of reducing agents in reaction buffers and the incubation of 1,4-benzoquinone with the enzyme prior to the addition of DNA. 1,4-Benzoquinone increased topoisomerase II-mediated DNA cleavage primarily by enhancing the forward rate of scission. In vitro, the compound induced cleavage at DNA sites proximal to a defined leukemic chromosomal breakpoint and displayed a sequence specificity that differed from that of etoposide. Finally, 1,4-benzoquinone stimulated DNA cleavage by topoisomerase IIalpha in cultured human cells. The present findings are consistent with the hypothesis that topoisomerase IIalpha plays a role in the initiation of specific leukemias induced by benzene and its metabolites.

Exposure of Tg.AC transgenic mice to benzene suppresses hematopoietic progenitor cells and alters gene expression in critical signaling pathways

The effects of acute benzene (BZ) exposure on hematopoietic progenitor cells (HPCs) derived from bone marrow cells were studied using homozygous male v-Ha-ras Tg.AC mice at 8-10 weeks of age. The mice were given 0.02% BZ in their drinking water for 28 days with the dose rate estimated to be 34 mg benzene/kg BW/day. Analysis of cultured HPCs indicated that BZ suppressed the proliferation of the multilineage colony forming unit-granulocyte, erythrocyte, macrophage, megakaryocyte (CFU-GEMM); colony forming unit-granulocyte, macrophage (CFU-GM); and blast forming unit erythrocyte/colony forming unit erythrocyte (BFUE/CFUE). A gene expression profile was generated using nylon arrays spotted with 23 cDNAs involved in selected signal pathways involved in cell distress, inflammation, DNA damage, cell cycle arrest, and apoptosis. Of the 23 marker genes, 6 (bax, c-fos, E124, hsf1, ikBa, and p57) were significantly (Mann-Whitney U tests, P < 0.05) overexpressed in BZ-exposed mice. Two genes (c-myc and IL-2) approached significance (at P = 0.053). The pattern of gene expression was consistent with BZ toxicity and the suppression of HPCs.

Volatile organic compounds in foods: a five year study

A purge and trap procedure was used with gas chromatography-mass spectrometry determination to analyze 70 foods for volatile organic compounds (VOCs). The results from analyses over a 5 year period (1996-2000) are reported. VOCs were found in at least one sample of all foods tested, although no single compound was found in each of the foods. The total amount of VOCs found in a single food item over the 5 year period ranged from 24 to 5328 ppb, with creamed corn (canned) the lowest and cheddar cheese the highest. Benzene was found in all foods except American cheese and vanilla ice cream. Benzene levels ranged from 1 to 190 ppb, with the highest level found in fully cooked ground beef. Benzene was found in 12 samples of cooked ground beef, with an average of 40 ppb. Benzene levels above 100 ppb were also seen in at least one sample each of a cola (138 ppb), raw bananas (132 ppb), and cole slaw (102 ppb). This compares to a maximum contaminant level of 5 ppb set by the U.S. EPA for drinking water.

Ex Vivo Immunotherapy for Patients with Benzene-Induced Aplastic Anemia

Aplastic anemia is a bone marrow failure disorder characterized by pancytopenia and a hypocellular marrow. Benzene is one of the etiologic agents capable of inducing the disease. With modest to severe aplastic anemia, one previously untreated patient and 13 patients who had failed immunosuppressive therapy were studied. Peripheral blood mononuclear cells from patients were expanded in vitro with a combination of cytokines and a calcium-mobilizing agents for 2 days, and the activated cells were infused intravenously once a week. In some cases, we used allogenic leukocytes instead of autologous cultured lymphocytes. After 6-35 weeks of the treatment, all patients had multilineage responses to this therapy and achieved complete disease remission, defined as normal blood count, independence from transfusion, and normal bone marrow histology. The therapy was safe and well tolerated with minimal side effects. The cultured cells produced interleukin-1 and induced immune responses in vivo. Serum interleukin-2 and interferon- gamma were detected following cell infusion. Finally, patients had sustained responses to the therapy and no relapse was found up to 18 months after cellular therapy.

Use of stable isotopically labeled benzene to evaluate environmental exposures

The use of stable, isotopically labeled compounds in controlled exposure experiments at environmentally relevant levels allows for the distinguishing of urinary metabolites associated with known exposure from background levels generally present in the urine. Exposures of volunteers to (13)C-benzene for 2 h at 40+/-10 p.p.b. were conducted after obtaining informed consent, and urinary phenol, catechol, hydroquinone and trans,trans- muconic acid were measured. Each isotopically labeled urinary metabolite was determined in the presence of significantly higher concentrations of the unlabeled metabolite. Following exposure, free and acid hydrolyzed phenol, acid hydrolyzed catechol and hydroquinone, and free trans,trans-muconic acid were determined by GC/MS. The percentage of trans,trans-muconic acid excreted was higher than reported following exposure at occupational levels. The use of isotopically labeled compounds has the potential to investigate the metabolism of common environmental contaminants for validation of toxicokinetic models and improve risk extrapolation from high concentration occupational exposures and animal studies to environmentally relevant pollutant levels.

Separate detection of BTX mixture gas by a microfluidic device using a function of nanosized pores of mesoporous silica adsorbent

We achieved separate detection of the components of 10 ppm of a benzene, toluene, and o-xylene mixture gas by using mesoporous silica powder incorporated in our microfluidic device. The device consists of concentration and detection cells formed of 3 cm x 1 cm Pyrex plates. We first introduced the mixture gas into the concentration cell where it was adsorbed on an adsorbent in a channel formed in the cell. We then raised the temperature using a thin-film heater and introduced the desorbed gas into the detection cell. Here, we measured the changes in the absorption spectra of the mixture gas in the detection cell. We found that the mixture ratio of the compounds in the desorbed gas varies with time because the thermal desorption property of each compound is different from that of the adsorbent. We analyzed the thermal desorption mechanism by comparing two types of silica adsorbents with different pore structures. We found that an adsorbent that has pores with a periodic and uniform nanosized column shape provides better component separation. We concluded that the uniform pore structure might cause the adsorbate molecules to exhibit a homogeneous adsorption state thus revealing the desorption properties of the gas more clearly.

Personal exposure to different levels of benzene and its relationships to the urinary metabolites S-phenylmercapturic acid and trans,trans-muconic acid

This report is part of an extensive study to verify the validity, specificity, and sensitivity of biomarkers of benzene at low exposures and assess their relationships with personal exposure and genetic damage. The study population was selected from benzene-exposed workers in Tianjin, China, based on historical exposure data. The recruitment of 130 exposed workers from glue-making or shoe-making plants and 51 unexposed subjects from nearby food factories was based on personal exposure measurements conducted for 3-4 weeks prior to collection of biological samples. In this report we investigated correlation of urinary benzene metabolites, S-phenylmercapturic acid (S-PMA) and trans,trans-muconic acid (t,t-MA) with personal exposure levels on the day of urine collection and studied the effect of dose on the biotransformation of benzene to these key metabolites. Urinary S-PMA and t,t-MA were determined simultaneously by liquid chromatography-tandem mass spectrometry analyses. Both S-PMA and t,t-MA, but specifically the former, correlated well with personal benzene exposure over a broad range of exposure (0.06-122 ppm). There was good correlation in the subgroup that had been exposed to <1 ppm benzene with both metabolites (P-trend <0.0001 for S-PMA and 0.006 for t,t-MA). Furthermore, the levels of S-PMA were significantly higher in the subgroup exposed to <0.25 ppm than that in unexposed subjects (n=17; P=0.001). There is inter-individual variation in the rate of conversion of benzene into urinary metabolites. The percentage of biotransformation of benzene to urinary S-PMA ranged from 0.005 to 0.3% and that to urinary t,t-MA ranged from 0.6 to approximately 20%. The percentage of benzene biotransformed into S-PMA and t,t-MA decreased with increasing concentration of benzene, especially conversion of benzene into t,t-MA. It appears that women excreted more metabolites than men for the same levels of benzene exposures. Our data suggest that S-PMA is superior to t,t-MA as a biomarker for low levels of benzene exposure.

Validated method for quantitation of biomarkers for benzene and its alkylated analogues in urine

A validated gas chromatography-mass spectrometric method for the analysis of the metabolites of benzene and its alkylated analogues in urine is reported. A number of metabolites, as required by authorities for biomonitoring of industrial exposure to aromatic vapour, were analysed simultaneously with preservation of quantitative information concerning positional isomers. The use of this method replaces a combination of analytical methods required for the analysis of all these metabolites. Urine samples were subjected to acidic deconjugation followed by a derivatization step. Phenol, ortho-, meta-, para-cresol, mandelic acid, and ortho-, meta-, para-methylhippuric acid were analysed as their corresponding ethoxycarbonyl derivatives, with single ion monitoring. The mass-to-charge ratios (m/z) of the ions used for quantitation by single ion monitoring of the metabolites were: phenol, 94 m/z; cresols, 108 m/z; mandelic acid, 206 m/z; hippuric acid, 105 m/z; methylhippuric acids, 119 m/z. The mass-to-charge ratios for the internal standards were: [(2)H(6)]phenol, 99 m/z; p-chlorophenol, 128 m/z and 3-chloro-4-hydroxyphenyl acetic acid, 214 m/z. The limits of detection for phenol and the cresols were below 0.4 micromol/l and below 0.05 micromol/l for mandelic acid and the hippuric acids. Within-run precision for mandelic acid was 6.2%, for hippuric acid was 7.32% and was below 5% for the rest of the analytes.

Catechol ortho-quinones: the electrophilic compounds that form depurinating DNA adducts and could initiate cancer and other diseases

Catechol estrogens and catecholamines are metabolized to quinones, and the metabolite catechol (1,2-dihydroxybenzene) of the leukemogenic benzene can also be oxidized to its quinone. We report here that quinones obtained by enzymatic oxidation of catechol and dopamine with horseradish peroxidase, tyrosinase or phenobarbital-induced rat liver microsomes react with DNA by 1,4-Michael addition to form predominantly depurinating adducts at the N-7 of guanine and the N-3 of adenine. These adducts are analogous to the ones formed with DNA by enzymatically oxidized 4-catechol estrogens (Cavalieri,E.L., et al. (1997) PROC: Natl Acad. Sci., 94, 10937). The adducts were identified by comparison with standard adducts synthesized by reaction of catechol quinone or dopamine quinone with deoxyguanosine or adenine. We hypothesize that mutations induced by apurinic sites, generated by the depurinating adducts, may initiate cancer by benzene and estrogens, and some neurodegenerative diseases (e.g. Parkinson's disease) by dopamine. These data suggest that there is a unifying molecular mechanism, namely, formation of specific depurinating DNA adducts at the N-7 of guanine and N-3 of adenine, that could initiate many cancers and neurodegenerative diseases.

NAD(P)H:quinone oxidoreductase (NQO1) polymorphism, exposure to benzene, and predisposition to disease: a HuGE review

NAD(P)H:quinone oxidoreductase (NQO1) catalyzes the two- or four-electron reduction of numerous endogenous and environmental quinones (e.g., the vitamin E alpha-tocopherol quinone, menadione, benzene quinones). In laboratory animals treated with various environmental chemicals, inhibition of NQO1 metabolism has long been known to increase the risk of toxicity or cancer. Currently, there are 22 reported single-nucleotide polymorphisms (SNPs) in the NQO1 gene. Compared with the human consensus (reference, "wild-type") NQO1*1 allele coding for normal NQO1 enzyme and activity, the NQO1*2 allele encodes a nonsynonymous mutation (P187S) that has negligible NQO1 activity. The NQO1*2 allelic frequency ranges between 0.22 (Caucasian) and 0.45 (Asian) in various ethnic populations. A large epidemiologic investigation of a benzene-exposed population has shown that NQO1*2 homozygotes exhibit as much as a 7-fold greater risk of bone marrow toxicity, leading to diseases such as aplastic anemia and leukemia. The extent of the contribution of polymorphisms in other genes involved in the metabolism of benzene and related compounds-such as the P450 2E1 (CYP2E1), myeloperoxidase (MPO), glutathione-S-transferase (GSTM1, GSTT1), microsomal epoxide hydrolase (EPHX1), and other genes-should also be considered. However, it now seems clear that a lowered or absent NQO1 activity can increase one's risk of bone marrow toxicity, after environmental exposure to benzene and benzene-like compounds. In cancer patients, the NQO1*2 allele appears to be associated with increased risk of chemotherapy-related myeloid leukemia. Many other epidemiological studies, attempting to find an association between the NQO1 polymorphism and one or another human disease, have now begun to appear in the medical literature.

Pharmacokinetic studies in Tg.AC and FVB mice administered [14C] benzene either by oral gavage or intradermal injection

Chronic benzene toxicity has been demonstrated to result in either aplastic anemia or acute myelogenous leukemia, a form of granulocytic leukemia, in exposed people (Snyder and Kalf, Crit. Rev. Toxicol. 24, 177-209, 1994). Aplastic anemia has been demonstrated in animal models following benzene exposure but, heretofore, it has not been possible to replicate benzene-induced granulocytic leukemia in animals. The Tg.AC mouse appears to be the first animal model in which a granulocytic leukemia was produced by treatment with benzene (Tennant et al., The Use of Short- and Medium-Term Tests for Carcinogenic Hazard Evaluation, 1999; French and Saulnier, J. Toxicol. Environ. Health 61, 377-379, 2000). Leukemia was observed in Tg.AC mice to which benzene was administered dermally. Neither orally dosed Tg.AC mice or mice of the parental FVB strain treated by either route of exposure developed leukemia. It is well established that benzene metabolism is required to produce benzene toxicity. To determine whether metabolic differences arising from differences in route of exposure or strain of mouse directed the development of leukemia, the pharmacokinetics of benzene were compared between the two strains and between the two routes of administration. Regardless of the route of exposure or the strain of mouse, seven major metabolites plus unmetabolized benzene were detected in most samples at most time points. Few differences were observed between the two strains following either route of administration. These results suggest that the genetic modification in the Tg.AC mouse, i.e., insertion of the v-Ha-ras construct into the genome, did not disrupt any major pathways involved in determining the pharmacokinetics of benzene. Two significant differences were observed between the two routes of exposure: first, benzene was absorbed more slowly after intradermal injection than after oral gavage, and second, the intradermally dosed mice produced more conjugates of hydroquinone than did the orally dosed mice. These differences in metabolism may be involved in the previously observed differences in hematotoxicity between the two routes of exposure.

Proliferation and differentiation of murine haemopoietic progenitor cells in stroma-free culture in the presence of metabolites of chlorinated pesticides

We have studied the influence of metabolites of chlorinated pesticides (lindane, pentachlorophenol, hexachlorobenzene) on proliferation and differentiation in two stroma-free murine bone marrow culture models, a multipotent progenitor cell line (FDCP-mix) and primary lineage-depleted bone marrow cells. Tetrachlorohydroquinone (Cl(4)pHQ), tetrachloro-p-benzoquinone (Cl(4p)BQ), but not their positional isomers, tetrachlorocatechol (Cl(4)oHQ) and tetrachloro-o-benzoquinone (Cl(4)oBQ), nor 2,4,6-trichlorophenol (2,4,6-Cl(3)P), were much more toxic to FDCP-mix cells cultured under conditions which lead to self-renewal than under conditions which lead to granulocyte-macrophage differentiation. Under the latter conditions, Cl(4)pHQ and Cl(4p)BQ even stimulated growth at intermediate concentration levels. In the primary cell cultures, pronounced differences were observed in the sensitivity between individual developmental pathways and between the different compounds. The percent of cells differentiating into the granulocytic lineage was increased at high concentration levels of each test compound. However, stimulatory effects on the macrophage lineage were observed at intermediate concentration levels of Cl(4)pHQ, Cl(4p)BQ and 2,4,6-Cl(3)P, and differentiation into erythrocytes was stimulated at low concentrations of 2,4,6-Cl(3)P. It is concluded that chlorinated monocyclic pesticides, after biotransformation to quinoid metabolites, may interact directly with haemopoietic progenitor cells with differential effects on self-renewal and differentiation. These mechanisms could lead to myeloplastic disorders.