In utero exposure to benzene disrupts fetal hematopoietic progenitor cell growth via reactive oxygen species

Hematopoietic stem cell discovery: unveiling the historical and future perspective of colony-forming units assay

Stem cells are special cells with the distinctive capability to self-renew, forming a new pool of undifferentiated stem cells. They are also able to differentiate into lineage-specific cell types that are specialized and matured. Thus, stem cells are considered as the building blocks of tissues and organs in which they reside. Among the many types of stem cells, hematopoietic stem cells (HSCs) are the most studied adult stem cells and are considered as a promising source of cells for applications in the clinical and basic sciences. Historically, research on HSCs was initiated in the 1940s, where in a groundbreaking experiment, intravenously injected bone marrow (BM) cells prevented the death of irradiated mice by restoring blood cell production. Since then, HSCs have been studied and utilized in medical therapies and research for over several decades. Over time, more sophisticated tools have been developed to evaluate the behaviour of specifically purified subsets of hematopoietic cells that have the capacity to produce blood cells. One of the established tools is the colony-forming units (CFUs) assay. This assay facilitates the identification, enumeration, and analysis of colonies formed by differentiated hematopoietic stem and progenitor cells (HSPCs) from myeloid, erythroid and lymphoid lineages. Hence, the CFUs assay is a fundamental in vitro platform that allows functional studies on the lineage potential of an individual HSPCs. The outcomes of such studies are crucial in providing critical insights into hematopoiesis. In this review, we explore the fundamental discoveries concerning the CFUs assay by covering the following aspects: (i) the historical overview of the CFUs assay for the study of clonal hematopoiesis involving multilineage potential of HSPCs, (ii) its use in various experimental models comprising humans, mice/rodents, zebrafish and induced pluripotent stem cells (iPSCs) and (iii) research gaps and future direction concerning the role of CFUs assay in clinical and basic sciences. Overall, the CFUs assay confers a transformative platform for a better understanding of HSPCs biology in governing hematopoiesis.

Oxidative stress and its role in recurrent pregnancy loss: mechanisms and implications

Recurrent pregnancy loss (RPL) is the occurrence of two or more consecutive miscarriages before 20 weeks of gestation. Recent research has increasingly focused on the role of oxidative stress in RPL, providing insights into its underlying mechanisms and potential therapeutic targets. Oxidative stress arises from an imbalance between reactive oxygen species (ROS) production and antioxidant defenses, leading to cellular damage and inflammation. Oxidative stress has been implicated in disrupting placental blood flow, inducing apoptosis in fetal and placental cells, and exacerbating inflammatory responses, all of which can contribute to pregnancy loss. Elevated levels of ROS have been associated with compromised placental function, impaired fetal development, and increased risk of RPL. Additionally, oxidative stress can modulate maternal immune responses, potentially leading to immune-related pregnancy complications. This review synthesizes current evidence on the mechanisms by which oxidative stress contributes to RPL and highlights emerging research on potential interventions, including antioxidant therapies and lifestyle modifications. Understanding these mechanisms is crucial for developing effective preventive and therapeutic strategies to reduce the risk of RPL and improve pregnancy outcomes. Future research should focus on elucidating the specific pathways involved and exploring novel treatments aimed at mitigating oxidative damage during pregnancy.

Identification of critical genes associated with oxidative stress pathways in benzene-induced hematotoxicity

Background and aims

Bone marrow failure (BMF) is chronic benzene-induced hematotoxicity, which is associated with differential gene expression abnormality. Benzene-induced BMF is characterized by irreversible bone marrow depression. Despite extensive studies have been conducted, there is a lack of reliable, useful and simple diagnostic method for BMF. Previous studies have shown that the aberrant gene expression changes and reactive oxygen species production in bone marrow cells related to the development of BMF. Early detection of differentially expressed genes (DEGs) as potential biomarkers is important for diagnosis and treatment. However, the validation of effective biomarker through DEGs analysis in benzene-induced BMF still deserve to be clarified. This study aimed to identify target genes as potential biomarkers with benzene-induced BMF based on DEGs analysis.

Methods

First, we developed a benzene-induced BMF mouse model and obtained the DEGs in bone marrow cells of benzene-exposed CD1 mice. Next, after obtaining the DEGs via RNA-Sequencing (RNA-seq) analysis, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis were also used, key genes associated with benzene-induced BMF were identified. Additionally, the key markers for benzene poisoning was evaluated using qRT-PCR technique.

Results

We identified DEGs for further KEGG functional analysis. Ten statistically significantly (up or down) regulated genes, namely Mapk11, Foxo1, Lefty1, Ren1, Bank1, Fgf3, Cdc42ep2, Rasgrf1, P2rx7, and Shank3 were found mainly associated with mitogen-activated protein kinases (MAPK) oxidative stress pathway . Further analysis using qRT-PCR identified that eight statistically significant DEGs associated with signaling pathways such as MAPK. We found that the level of mRNA expression of Mapk11, Foxo1, Bank1, Lefty1, Ren1, P2rx7, and Fgf3 genes were increased and Cdc42ep2 gene was decreased in BMF mice compared to control mice. Additionally, we validated the eight candidate genes for potential biomarkers in peripheral blood mononuclear cells of benzene poisoning patients by qRT-PCR.

Conclusion

Our results indicated that Mapk11 and Fgf3 were predominantly candidate genes linked to novel biomarkers for benzene hematotoxicity in human beings. Our study will provide new candidate genes as useful biomarkers involved in benzene-induced hematotoxicity.

An umbrella review of the evidence associating occupational carcinogens and cancer risk at 19 anatomical sites

Occupational exposure to carcinogens of increasing cancer risk have been extensively suggested. A robust assessment of these evidence is needed to guide public policy and health care. We aimed to classify the strength of evidence for associations of 13 occupational carcinogens (OCs) and risk of cancers. We searched PubMed and Web of Science up to November 2022 to identify potentially relevant studies. We graded the evidence into convincing, highly suggestive, suggestive, weak, or not significant according to a standardized classification based on: random-effects p value, number of cancer cases, 95% confidence interval of largest study, heterogeneity between studies, 95% prediction interval, small study effect, excess significance bias and sensitivity analyses with credibility ceilings. The quality of meta-analysis was evaluated by AMSTAR 2. Forty-eight articles yielded 79 meta-analyses were included in current umbrella review. Evidence of associations were convincing (class I) or highly suggeastive (class II) for asbestos exposure and increasing risk of lung cancer among smokers (RR = 8.79, 95%CI: 5.81-13.25 for cohort studies and OR = 8.68, 95%CI: 5.68-13.24 for case-control studies), asbestos exposure and increasing risk of mesothelioma (RR = 4.61, 95%CI: 2.57-8.26), and formaldehyde exposure and increasing risk of sinonasal cancer (RR = 1.68, 95%CI: 1.38-2.05). Fifteen associations were supported by suggestive evidence (class III). In summary, the current umbrella review found strong associations between: asbestos exposure and increasing risk of lung cancer among smokers; asbestos exposure and increasing risk of mesothelioma; and formaldehyde exposure and higher risk of sinonasal cancer. Other associations might be genuine, but substantial uncertainty remains.

Non-coding RNAs: A new frontier in benzene-mediated toxicity

One of the most frequent environmental contaminants, benzene is still widely used as an industrial solvent around the world, especially in developing nations, posing a serious occupational risk. While the processes behind the toxicity of benzene grounds are not fully understood, it is generally accepted that its metabolism, which involves one or more reactive metabolites, is crucial to its toxicity. In order to evaluate the many ways that benzene could influence gene regulation and thus have an impact on human health, new methodologies have been created. The pathophysiology of the disorder may result from epigenetic reprogramming caused by exposure to benzene, including changes in non-coding RNA (ncRNA) markers, according to recent studies. We are interested in the identification of hazardous regulatory ncRNAs, the identification of these ncRNAs' targets, and the comprehension of the significance of these interactions in the mechanisms behind benzene toxicity. Hence, the focus of recent research is on long non-coding RNAs (lncRNAs), circular RNAs (circRNAs) and microRNAs (miRNAs), and some of the more pertinent articles are also discussed.

Adult-Onset Transcriptomic Effects of Developmental Exposure to Benzene in Zebrafish (Danio rerio): Evaluating a Volatile Organic Compound of Concern

Urban environments are afflicted by mixtures of anthropogenic volatile organic compounds (VOCs). VOC sources that drive human exposure include vehicle exhaust, industrial emissions, and oil spillage. The highly volatile VOC benzene has been linked to adverse health outcomes. However, few studies have focused on the later-in-life effects of low-level benzene exposure during the susceptible window of early development. Transcriptomic responses during embryogenesis have potential long-term consequences at levels equal to or lower than 1 ppm, therefore justifying the analysis of adult zebrafish that were exposed during early development. Previously, we identified transcriptomic alteration following controlled VOC exposures to 0.1 or 1 ppm benzene during the first five days of embryogenesis using a zebrafish model. In this study, we evaluated the adult-onset transcriptomic responses to this low-level benzene embryogenesis exposure (n = 20/treatment). We identified key genes, including col1a2 and evi5b, that were differentially expressed in adult zebrafish in both concentrations. Some DEGs overlapped at the larval and adult stages, specifically nfkbiaa, mecr, and reep1. The observed transcriptomic results suggest dose- and sex-dependent changes, with the highest impact of benzene exposure to be on cancer outcomes, endocrine system disorders, reproductive success, neurodevelopment, neurological disease, and associated pathways. Due to molecular pathways being highly conserved between zebrafish and mammals, developmentally exposed adult zebrafish transcriptomics is an important endpoint for providing insight into the long term-effects of VOCs on human health and disease.

Identification of Cellular Compositions in Different Microenvironments and Their Potential Impacts on Hematopoietic Stem Cells HSCs Using Single-Cell RNA Sequencing with Systematical Confirmation

Hematopoietic stem cells (HSCs) are stem cells that can differentiate into various blood cells and have long-term self-renewal capacity. At present, HSC transplantation is an effective therapeutic means for many malignant hematological diseases, such as aplastic hematological diseases and autoimmune diseases. The hematopoietic microenvironment affects the proliferation, differentiation, and homeostasis of HSCs. The regulatory effect of the hematopoietic microenvironment on HSCs is complex and has not been thoroughly studied yet. In this study, we focused on mononuclear cells (MNCs), which provided an important microenvironment for HSCs and established a methodological system for identifying cellular composition by means of multiple technologies and methods. First, single-cell RNA sequencing (scRNA-seq) technology was used to investigate the cellular composition of cells originating from different microenvironments during different stages of hematopoiesis, including mouse fetal liver mononuclear cells (FL-MNCs), bone marrow mononuclear cells (BM-MNCs), and in vitro-cultured fetal liver stromal cells. Second, bioinformatics analysis showed a higher proportion and stronger proliferation of the HSCs in FL-MNCs than those in BM-MNCs. On the other hand, macrophages in in vitro-cultured fetal liver stromal cells were enriched to about 76%. Differential gene expression analysis and Gene Ontology (GO) functional enrichment analysis demonstrated that fetal liver macrophages have strong cell migration and actin skeleton formation capabilities, allowing them to participate in the hematopoietic homeostasis through endocytosis and exocytosis. Last, various validation experiments such as quantitative real-time PCR (qRT-PCR), ELISA, and confocal image assays were performed on randomly selected target genes or proteins secreted by fetal liver macrophages to further demonstrate the potential relationship between HSCs and the cells inhabiting their microenvironment. This system, which integrates multiple methods, could be used to better understand the fate of these specific cells by determining regulation mechanism of both HSCs and macrophages and could also be extended to studies in other cellular models.

Linking Benzene, in Utero Carcinogenicity and Fetal Hematopoietic Stem Cell Niches: A Mechanistic Review

Previous research reported that prolonged benzene exposure during in utero fetal development causes greater fetal abnormalities than in adult-stage exposure. This phenomenon increases the risk for disease development at the fetal stage, particularly carcinogenesis, which is mainly associated with hematological malignancies. Benzene has been reported to potentially act via multiple modes of action that target the hematopoietic stem cell (HSCs) niche, a complex microenvironment in which HSCs and multilineage hematopoietic stem and progenitor cells (HSPCs) reside. Oxidative stress, chromosomal aberration and epigenetic modification are among the known mechanisms mediating benzene-induced genetic and epigenetic modification in fetal stem cells leading to in utero carcinogenesis. Hence, it is crucial to monitor exposure to carcinogenic benzene via environmental, occupational or lifestyle factors among pregnant women. Benzene is a well-known cause of adult leukemia. However, proof of benzene involvement with childhood leukemia remains scarce despite previously reported research linking incidences of hematological disorders and maternal benzene exposure. Furthermore, accumulating evidence has shown that maternal benzene exposure is able to alter the developmental and functional properties of HSPCs, leading to hematological disorders in fetus and children. Since HSPCs are parental blood cells that regulate hematopoiesis during the fetal and adult stages, benzene exposure that targets HSPCs may induce damage to the population and trigger the development of hematological diseases. Therefore, the mechanism of in utero carcinogenicity by benzene in targeting fetal HSPCs is the primary focus of this review.

Linalool reverses benzene-induced cytotoxicity, oxidative stress and lysosomal/mitochondrial damages in human lymphocytes

Benzene exposure results in bone marrow suppression, leading to a decrease in the number of circulating white blood cells, an increased risk of chronic lymphocytic leukemia, acute myeloid leukemia and aplastic anemia. Since the mechanism of induction of benzene toxicity is due to active metabolites through cytochrome p450 enzymes and production of reactive oxygen species (ROS), we hypothesized that natural compound such linalool with anti-inflammatory/antioxidant properties could be effective in reducing its toxicity. Lymphocytes isolated from healthy individuals were simultaneously cotreated with different concentrations of LIN (10, 25 and 50 µM) and benzene (50 µM) for 4 h at 37 °C. After incubation, the toxicity parameters such cytotoxicity, ROS formation, lysosomal membrane integrity, mitochondria membrane potential (ΔΨm) collapse, oxidized/reduced glutathione (GSH/GSSG) and malondialdehyde (MDA) were analyzed using biochemical and flow cytometry evaluations. Our data showed that benzene (50 µM) induced a significant increase in cytotoxicity, ROS formation, mitochondrial membrane potential (MMP) collapse, lipid peroxidation and oxidative stress while LIN with antioxidant potential reversed the toxic effects of benzene on isolated human lymphocytes. Our results suggest that LIN reduces and reverses benzene-induced cytotoxicity, oxidative stress and lysosomal/mitochondrial damages in human lymphocyte. This study demonstrated that cotreatment of LIN with benzene can reduce several parameters indicative of oxidative stress. As such, LIN could represent a potential therapeutic agent in reducing certain aspects of benzene-induced toxicity.

Exposure to outdoor air pollution at different periods and the risk of leukemia: a meta-analysis

The causes of leukemia remain largely unknown; our aims were to examine the association between the exposure to outdoor air pollution and leukemia risk and to explore the effect of this exposure during different periods of pregnancy and early life. We searched for all case-control and cohort studies published before February 20, 2021, which measured the risk of leukemia in relation to exposure to the air pollutants: particulate matter, benzene, nitrogen dioxide (NO₂), and nitrogen oxides (NO_x). We then carried out a meta-analysis and calculated the summary relative risks (RRs) of leukemia by using a random-effects model. The potential dose-response relationship was further explored. The results showed that the highest exposure to benzene (RR: 1.20, 95%CI: 1.06-1.35) and NO₂ (RR: 1.04, 95%CI; 1.02-1.08) were positively correlated with leukemia risk when compared to the lowest exposure categories for each air pollutant. During pregnancy, exposure to benzene in the third trimester, as well as exposure to NO₂ in the second trimester and entire pregnancy, could also increase the risk of leukemia. In the dose-response analysis, benzene exposure and NO₂ exposure were linearly associated with the risk of leukemia. Other air pollutants did not have a statistical correlation with leukemia risk. There was a certain degree of publication bias in studies on benzene. Overall, our results support a link between outdoor air pollution and leukemia risk, particularly due to benzene and NO₂. Prospero Registration Number: PROSPERO CRD42020207025.

Benzene and its effects on cell signaling pathways related to hematopoiesis and leukemia

Benzene is an environmental toxicant found in many consumer products. It is an established human carcinogen and is known to cause acute myeloid leukemia in adults. Epidemiological evidence has since shown that benzene can cross the placenta and affect the fetal liver. Animal studies have shown that in utero exposure to benzene can increase tumor incidence in offspring. Although there have been risk factors established for acute myeloid leukemia, they still do not account for many of the cases. Clearly then, current efforts to elucidate the mechanism by which benzene exerts its carcinogenic properties have been superficial. Owing to the critical role of cell signaling pathways in the development of an organism and its various organ systems, it seems plausible to suspect that these pathways may have a role in leukemogenesis. This review article assesses current evidence of the effects of benzene on critical hematopoietic signaling pathways. Pathways discussed included Hedgehog, Notch/Delta, Wingless/Integrated, nuclear factor-kappaB and others. Following a review of the literature, it seems that current evidence about the effects of benzene on these critical signaling pathways remains limited. Given the important role of these pathways in hematopoiesis, more attention should be given to them.

Evaluation of immunological, inflammatory, and oxidative stress biomarkers in gasoline station attendants

Background

Gasoline is a complex mixture of saturated and unsaturated hydrocarbons, in which aromatic compounds, such as BTX (benzene, toluene, and xylene) feature as the main constituents. Simultaneous exposure to these aromatic hydrocarbons causes a significant impact on benzene toxicity. In order to detect early alterations caused in gasoline station attendants exposed to BTX compounds, immunological, inflammatory, and oxidative stress biomarkers were evaluated.

Methods

A total of 66 male subjects participated in this study. The gasoline station attendants (GSA) group consisted of 38 gasoline station attendants from Rio Grande do Sul, Brazil. The non-exposed group consisted of 28 subjects who were non-smokers and who had no history of occupational exposure. Environmental and biological monitoring of BTX exposure was performed using blood and urine.

Results

The GSA group showed increased BTX concentrations in relation to the non-exposed group (p < 0.001). The GSA group showed elevated protein carbonyl (PCO) levels and pro-inflammatory cytokines, decreased expression of CD80 and CD86 in monocytes, and reduced glutathione S-transferase (GST) activity compared to the non-exposed group (p < 0.05). BTX levels and trans,trans-muconic acid levels were positively correlated with pro-inflammatory cytokines and negatively correlated with interleukin-10 contents (p < 0.001). Increased levels of pro-inflammatory cytokines were accompanied by increased PCO contents and decreased GST activity (p < 0.001). Furthermore, according to the multiple linear regression analysis, benzene exposure was the only factor that significantly contributed to the increased pro-inflammatory cytokines (p < 0.05).

Conclusions

Taken together, these findings show the influence of exposure to BTX compounds, especially benzene, on the immunological, inflammatory, and oxidative stress biomarkers evaluated. Furthermore, the data suggest the relationship among the evaluated biomarkers of effect, which could contribute to providing early signs of damage to biomolecules in subjects occupationally exposed to BTX compounds.

DNA Damage and Perturbed Topoisomerase IIα as a Target of 1,4-Benzoquinone Toxicity in Murine Fetal Liver Cells

Benzene is a ubiquitous environmental pollutant. Recent studies have shown a link between the development of childhood leukemias and maternal benzene exposure, suggesting that these leukemias may be initiated in utero. Benzene crosses the placental barrier however the mechanisms behind in utero benzene toxicity have not been well elucidated. This study is the first to show that the benzene metabolite, benzoquinone (BQ), perturbs fetal topoisomerase IIα (Topo IIα), an enzyme essential for DNA repair. Using cultured murine CD-1 fetal liver cells, this study shows that Topo IIα activity decreases following 24 hours of exposure to BQ (12.5 and 15.625 µM), with the 12.5 µM confirmed to disrupt the c-kit+Lin-Sca-1-Il7rα- population of cells in culture. Pre-treatment with the antioxidant, N-acetylcysteine did not prevent the inhibtion of Topo IIα by BQ. An increase in Topo IIα-DNA covalent adducts was detected following 24-hour exposures to BQ (12.5 and 50 µM). Interestingly, BQ (12.5 µM) exposure did not significantly increase levels of 4-hydroxynonenal (4-HNE), a marker of oxidative stress after 24 hours. However, increased levels of the double-stranded DNA break marker γH2AX were detected following 24 hours of BQ exposure, confirming that Topo IIα-induced breaks are increased in BQ treated cells. This study shows that fetal Topo IIα is perturbed by BQ and suggests that this protein is a target of benzene and may be implicated with in utero benzene toxicity.

Comprehensive Proteomic Characterization of Ontogenic Changes in Hematopoietic Stem and Progenitor Cells

Hematopoietic stem and progenitor cells (HSPCs) in the fetus and adult possess distinct molecular landscapes that regulate cell fate and change their susceptibility to initiation and progression of hematopoietic malignancies. Here, we applied in-depth quantitative proteomics to comprehensively describe and compare the proteome of fetal and adult HSPCs. Our data uncover a striking difference in complexity of the cellular proteomes, with more diverse adult-specific HSPC proteomic signatures. The differential protein content in fetal and adult HSPCs indicate distinct metabolic profiles and protein complex stoichiometries. Additionally, adult characteristics include an arsenal of proteins linked to viral and bacterial defense, as well as protection against ROS-induced protein oxidation. Further analyses show that interferon α, as well as Neutrophil elastase, has distinct functional effects in fetal and adult HSPCs. This study provides a rich resource aimed toward an enhanced mechanistic understanding of normal and malignant hematopoiesis during fetal and adult life.

Functional Assays of Hematopoietic Stem Cells in Toxicology Research

The hematopoietic stem cell is the foundational cell of the entire blood and immune system and as such is particularly sensitive to toxicological insults. While this review will identify some of the classes of chemicals known to be hematotoxic, most of the discussion will focus on the strengths and weaknesses of various hematological assays used in toxicology research. Furthermore, protocols for isolating both human and murine hematopoietic stem cells are described. Methodologies are also described for various culture systems useful for testing the impacts of potential toxicants on hematopoietic stem cells both in vivo and in vitro.

Benzene exposure is associated with cardiovascular disease risk

Benzene is a ubiquitous, volatile pollutant present at high concentrations in toxins (e.g. tobacco smoke) known to increase cardiovascular disease (CVD) risk. Despite its prevalence, the cardiovascular effects of benzene have rarely been studied. Hence, we examined whether exposure to benzene is associated with increased CVD risk. The effects of benzene exposure in mice were assessed by direct inhalation, while the effects of benzene exposure in humans was assessed in 210 individuals with mild to high CVD risk by measuring urinary levels of the benzene metabolite trans,trans-muconic acid (t,t-MA). Generalized linear models were used to assess the association between benzene exposure and CVD risk. Mice inhaling volatile benzene had significantly reduced levels of circulating angiogenic cells (Flk-1⁺/Sca-1⁺) as well as an increased levels of plasma low-density lipoprotein (LDL) compared with control mice breathing filtered air. In the human cohort, urinary levels of t,t-MA were inversely associated several populations of circulating angiogenic cells (CD31⁺/34⁺/45⁺, CD31⁺/34⁺/45⁺/AC133^–, CD34⁺/45⁺/AC133⁺). Although t,t-MA was not associated with plasma markers of inflammation or thrombosis, t,t-MA levels were higher in smokers and in individuals with dyslipidemia. In smokers, t,t-MA levels were positively associated with urinary metabolites of nicotine (cotinine) and acrolein (3-hydroxymercapturic acid). Levels of t,t-MA were also associated with CVD risk as assessed using the Framingham Risk Score and this association was independent of smoking. Thus, benzene exposure is associated with increased CVD risk and deficits in circulating angiogenic cells in both smokers and non-smokers.

The Yiqi and Yangyin Formula ameliorates injury to the hematopoietic system induced by total body irradiation

In this study, we examined whether the Yiqi and Yangyin Formula (YYF), used in traditional Chinese medicine, could ameliorate damage to the hematopoietic system induced by total body irradiation (TBI). Treatment with 15 g/kg of YYF increased the survival rate of Institute of Cancer Research (ICR) mice exposed to 7.5 Gy TBI. Furthermore, YYF treatment increased the white blood cell (WBC), red blood cell (RBC), hemoglobin (HGB) and hematocrit (HCT) counts in ICR mice exposed to 2 Gy or 4 Gy TBI. Treatment with YYF also increased the number of bone marrow cells, hematopoietic progenitor cells (HPCs), hematopoietic stem cells (HSCs) and the colony-forming ability of granulocyte-macrophage cells. YYF alleviated TBI-induced suppression of the differentiation ability of HPCs and HSCs and decreased the reactive oxygen species (ROS) levels in bone marrow mononuclear cells (BMMNCs), HPCs and HSCs from mice exposed to 2 Gy or 4 Gy TBI. Overall, our data suggest that YYF can ameliorate myelosuppression by reducing the intracellular ROS levels in hematopoietic cells after TBI at doses of 2 Gy and 4 Gy.

Parental, In Utero, and Early-Life Exposure to Benzene and the Risk of Childhood Leukemia: A Meta-Analysis

Benzene is an established cause of adult leukemia, but whether it is associated with childhood leukemia remains unclear. We conducted a meta-analysis in which we reviewed the epidemiologic literature on this topic and explored causal inference, bias, and heterogeneity. The exposure metrics that we evaluated included occupational and household use of benzenes and solvents, traffic density, and traffic-related air pollution. For studies of occupational and household product exposure published from 1987 to 2014, the summary relative risk for childhood leukemia was 1.96 (95% confidence interval (CI): 1.53, 2.52; n = 20). In these studies, the summary relative risk was higher for acute myeloid leukemia (summary relative risk (sRR) = 2.34, 95% CI: 1.72, 3.18; n = 6) than for acute lymphoblastic leukemia (sRR = 1.57; 95% CI: 1.21, 2.05; n = 14). The summary relative risk was higher for maternal versus paternal exposure, in studies that assessed benzene versus all solvents, and in studies of gestational exposure. In studies of traffic density or traffic-related air pollution published from 1999 to 2014, the summary relative risk was 1.48 (95% CI: 1.10, 1.99; n = 12); it was higher for acute myeloid leukemia (sRR = 2.07; 95% CI: 1.34, 3.20) than for acute lymphoblastic leukemia (sRR = 1.49; 95% CI: 1.07, 2.08) and in studies that involved detailed models of traffic pollution (sRR = 1.70; 95% CI: 1.16, 2.49). Overall, we identified evidence of associations between childhood leukemia and several different potential metrics of benzene exposure.

Estimation of residue depletion of cyadox and its marker residue in edible tissues of pigs using physiologically based pharmacokinetic modelling

Physiologically based pharmacokinetic (PBPK) models are powerful tools to predict tissue distribution and depletion of veterinary drugs in food animals. However, most models only simulate the pharmacokinetics of the parent drug without considering their metabolites. In this study, a PBPK model was developed to simultaneously describe the depletion in pigs of the food animal antimicrobial agent cyadox (CYA), and its marker residue 1,4-bisdesoxycyadox (BDCYA). The CYA and BDCYA sub-models included blood, liver, kidney, gastrointestinal tract, muscle, fat and other organ compartments. Extent of plasma-protein binding, renal clearance and tissue-plasma partition coefficients of BDCYA were measured experimentally. The model was calibrated with the reported pharmacokinetic and residue depletion data from pigs dosed by oral gavage with CYA for five consecutive days, and then extrapolated to exposure in feed for two months. The model was validated with 14 consecutive day feed administration data. This PBPK model accurately simulated CYA and BDCYA in four edible tissues at 24-120 h after both oral exposure and 2-month feed administration. There was only slight overestimation of CYA in muscle and BDCYA in kidney at earlier time points (6-12 h) when dosed in feed. Monte Carlo analysis revealed excellent agreement between the estimated concentration distributions and observed data. The present model could be used for tissue residue monitoring of CYA and BDCYA in food animals, and provides a foundation for developing PBPK models to predict residue depletion of both parent drugs and their metabolites in food animals.

Investigating the effects of in utero benzene exposure on epigenetic modifications in maternal and fetal CD-1 mice

Exposure to the ubiquitous environmental pollutant benzene is positively correlated with leukemia in adults and may be associated with childhood leukemia following in utero exposure. While numerous studies implicate oxidative stress and DNA damage as playing a role in benzene-mediated carcinogenicity, emerging evidence suggests that alterations in epigenetic regulations may be involved. The present study aimed to determine whether DNA methylation and/or various histone modifications were altered following in utero benzene exposure in CD-1 mice. Global DNA methylation and promoter-specific methylation of the tumor suppressor gene, p15, were assessed. Additionally, levels of acetylated histones H3, H4, and H3K56, as well as methylated histones H3K9 and H3K27 were assessed by Western blotting. A significant decrease in global DNA methylation of maternal bone marrow was observed following benzene exposure; however no effect on global DNA methylation was detected in fetal livers. Additionally, no effect of benzene exposure was observed on p15 promoter methylation or any measured histone modifications in both maternal bone marrow and fetal livers. These results suggest that the methodology used in the present study did not reveal alterations in DNA methylation and histone modifications following in utero exposure to benzene; however further experimentation investigating these modifications at the whole genome/epigenome level, as well as at later stages of benzene-induced carcinogenesis, are warranted.

Altered Expression of Genes in Signaling Pathways Regulating Proliferation of Hematopoietic Stem and Progenitor Cells in Mice with Subchronic Benzene Exposure

Leukemias and hematopoietic disorders induced by benzene may arise from the toxicity of benzene to hematopoietic stem or progenitor cells (HS/PCs). Since there is a latency period between initial benzene exposure and the development of leukemia, subsequent impact of benzene on HS/PCs are crucial for a deeper understanding of the carcinogenicity and hematotoxicity in post-exposure stage. This study aims to explore the effects of benzene on HS/PCs and gene-expression in Wnt, Notch and Hh signaling pathways in post-exposure stage. The C3H/He mice were injected subcutaneously with benzene (0, 150, 300 mg/kg/day) for three months and were monitored for another 10 months post-exposure. The body weights were monitored, the relative organ weights, blood parameters and bone marrow smears were examined. Frequency of lineage^- sca-1⁺ c-kit⁺ (LSK) cells, capability of colony forming and expression of genes in Wnt, Notch and Hedghog (Hh) signaling pathways were also analyzed. The colony formation of the progenitor cells for BFU-E, CFU-GEMM and CFU-GM was significantly decreased with increasing benzene exposure relative to controls, while no significant difference was observed in colonies for CFU-G and CFU-M. The mRNA level of cyclin D1 was increased and Notch1 and p53 were decreased in LSK cells in mice exposed to benzene but with no statistical significance. These results suggest that subsequent toxic effects of benzene on LSK cells and gene expression in Wnt, Notch and Hh signaling pathways persist in post-exposure stage and may play roles in benzene-induced hematotoxicity.

Metabolic Disposition and Elimination of Cyadox in Pigs, Chickens, Carp, and Rats

The metabolism, distribution, and elimination of cyadox (CYA) is investigated in pigs, chickens, carp, and rats to identify the marker residue and target tissue of CYA in food animals for food safety concerns. Following a single oral gavage of [(3)H]-CYA, the total radioactivity was rapidly excreted, with more than 95% of the dose excreted within 14 days in the four species. Fecal excretion of the total radioactivity was 66.2% and 51.6%, and urinary excretion of the total radioactivity was 28.35% and 44.3% in rats and pigs, respectively. Radioactivity was observed in nearly all of the tissues in the first 6 h after 7 days of consecutive oral dosing. The highest radioactivity and longest persistence were in the livers and kidneys, where the majority of the radioactivity was cleared within 7 days. A total of 15 metabolites were identified in rats, pigs, chickens, and carp, and eight new metabolites were identified for the first time in vivo. No parent drug could be detected in the tissues of rats and pigs. The major metabolites of CYA were Cy1, Cy3, and Cy6 in pigs, Cy1, Cy5, and Cy6 in chickens, Cy1, Cy2, and Cy4 in carp, and Cy1, Cy2, Cy4, and Cy5 in rats. Cy1 was suggested to be the marker residue, and the kidneys were identified as the target tissue of CYA in pigs and chickens. These results provide comprehensive information for the food safety evaluation of CYA in food animals and will improve the understanding of the pharmacology and toxicology of CYA in animals.

1,4-benzoquinone-induced STAT-3 hypomethylation in AHH-1 cells: Role of oxidative stress

Benzene, a known occupational and environmental contaminant, is associated with increased risk of leukemia. The objectives of this study were to elucidate the regulatory mechanism of the hypomethylated STAT3 involved in benzene toxicity in vitro. As 1,4-benzoquinone (1,4-BQ) is one of benzene’s major toxic metabolites, AHH-1 cells were treated by 1,4-BQ for 24 h with or without pretreatment of the antioxidant a-LA or the methyltransferase inhibitor, 5-aza-2′ deoxycytidine (5-aza). The cell viability was investigated using the 3-(4, 5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. ROS was determined via 2′,7′-dichlorodihydrofluorescein diacetate (DCFDA) flow cytometric assays. The level of oxidative stress marker 8-OHdG was measured by enzyme-linked immunosorbent assay. Methylation-specific PCR was used to detect the methylation status of STAT3. Results indicated the significantly increasing expression of ROS and 8-OHdG which accompanied with STAT3 hypomethylation in 1,4-BQ-treated AHH-1 cells. α-LA suppressed the expression of both ROS and 8-OHdG, simultaneously reversed 1,4-BQ-induced STAT3 hypomethylation. However, although the methylation inhibitor, 5-aza reduced the expression level of ROS and 8-OHdG, but had no obvious inhibiting effect on STAT3 methylation level. Taken together, oxidative stress are involved 1,4-BQ-induced STAT3 methylation expression.

Regulation of PKM2 and Nrf2-ARE pathway during benzoquinone induced oxidative stress in yolk sac hematopoietic stem cells

Benzene is an occupational toxicant and an environmental pollutant that is able to induce the production of reactive oxygen species (ROS), causing oxidative stress and damages of the macromolecules in target cells, such as the hematopoietic stem cells. We had previously found that embryonic yolk sac hematopoietic stem cells (YS-HSCs) are more sensitive to benzene toxicity than the adult bone marrow hematopoietic stem cells, and that nuclear factor-erythroid-2-related factor 2 (Nrf2) is the major regulator of cytoprotective responses to oxidative stress. In the present report, we investigated the effect of PKM2 and Nrf2-ARE pathway on the cellular antioxidant response to oxidative stress induced by benzene metabolite benzoquinone (BQ) in YS-HSC isolated from embryonic yolk sac and enriched by magnetic-activated cell sorting (MACS). Treatment of the YS-HSC with various concentrations of BQ for 6 hours induces ROS generation in a dose-dependent manner. Additional tests showed that BQ is also capable of inducing expression of NADPH oxidase1 (NOX1), and several other antioxidant enzymes or drug-metabolizing enzymes, including heme oxygenase 1 (HMOX1), superoxide dismutase (SOD), catalase and NAD(P)H dehydrogenase quinone 1 (NQO1). Concomitantly, only the expression of PKM2 protein was decreased by the treatment of BQ but not the PKM2 mRNA, which suggested that BQ may induce PKM2 degradation. Pretreatment of the cells with antioxidant N-acetylcysteine (NAC) decreased ROS generation and prevented BQ-induced PKM2 degradation, suggesting involvement of ROS in the PKM2 protein degradation in cellular response to BQ. These findings suggest that BQ is a potent inducer of ROS generation and the subsequent antioxidant responses of the YS-HSC. The accumulated ROS may attenuate the expression of PKM2, a key regulator of the pyruvate metabolism and glycolysis.

The LINA cohort: Cord blood eosinophil/basophil progenitors predict respiratory outcomes in early infancy

RATIONALE

Cord blood eosinophil/basophil progenitor cells (Eo/B) of high risk infants have been shown to predict respiratory illnesses in infancy. Here we investigated this association in a population-based cohort. Furthermore, we analysed whether newborns Th1/Th2 balance and prenatal environmental exposure impact Eo/B recruitment.

METHODS

In a sub-cohort of the LINA study cord blood mononuclear cells were used for methylcellulose assays to assess Eo/B differentiation. Questionnaires were recorded during pregnancy and annually thereafter. Volatile organic compounds were measured during pregnancy and cord blood cytokines after ex vivo stimulation.

RESULTS

Cord blood IL-4 and IL-13 positively correlated with Eo/B. Tobacco smoke related benzene was also positively associated with Eo/B. Enhanced Eo/B numbers increased the risk for wheezing within the first 24 months.

CONCLUSIONS

The association between cord blood Eo/B and respiratory illnesses is not restricted to high-risk children. Prenatal environmental exposure and a Th2 milieu at birth contribute to Eo/B recruitment.

Application of toxicogenomic profiling to evaluate effects of benzene and formaldehyde: from yeast to human

Genetic variation underlies a significant proportion of the individual variation in human susceptibility to toxicants. The primary current approaches to identify gene-environment (GxE) associations, genome-wide association studies and candidate gene association studies, require large exposed and control populations and an understanding of toxicity genes and pathways, respectively. This limits their application in the study of GxE associations for the leukemogens benzene and formaldehyde, whose toxicity has long been a focus of our research. As an alternative approach, our published work has applied innovative in vitro functional genomics testing systems, including unbiased functional screening assays in yeast and a near-haploid human bone marrow cell line. Through comparative genomic and computational analyses of the resulting data, human genes and pathways that may modulate susceptibility to benzene and formaldehyde were identified, and the roles of several genes in mammalian cell models were validated. In populations occupationally exposed to low levels of benzene, we applied peripheral blood mononuclear cell transcriptomics and chromosome-wide aneuploidy studies in lymphocytes. In this review, we describe our comprehensive toxicogenomic approach and the potential mechanisms of toxicity and susceptibility genes identified for benzene and formaldehyde, as well as related studies conducted by other researchers.

Cytotoxic effects of benzene metabolites on human sperm function: an in vitro study

In recent years, individuals are rampantly exposed to vapours of benzene, through paint, plastic, petroleum industries, fuel exhaust, and tobacco smoke. Hence the present investigation was directed towards determining the effect of benzene metabolites, namely, phenol-hydroquinone and catechol, on the motility, viability, and nuclear integrity of the human spermatozoa. From the results obtained it was clear that exposure to phenol-hydroquinone caused a significant decline in both, sperm motility and viability. Exposure to a phenol-hydroquinone (Phase I) microenvironment may therefore inhibit metabolically active enzymes, thus impeding ATP production, and in turn lowers sperm motility and viability. In addition, the present study also revealed that both metabolites of benzene caused significant denaturation of sperm nuclear DNA. Hence, exposure to phenol-hydroquinone in vitro could have resulted in generation of free radicals and altered membrane function, which is reflected by a decline in the motility, viability, and loss of sperm nuclear DNA integrity. In Phase II, the exposure of human sperm in vitro to varied concentrations of catechol caused only insignificant changes in sperm motility and viability as compared to those observed on exposure to phenol-hydroquinone. Hence, exposure to catechol appeared to have less toxic effects than those of phenol-hydroquinone.

Allergy and risk of acute lymphoblastic leukemia among children: a nationwide case control study in Greece

BACKGROUND

Several reports point to inverse associations between allergies and ALL; yet, no study has explored this link using both self-reported-data on allergic history and biomarkers of atopic sensitization.

METHODS

Clinical information for the variables of interest was available for 252 out of 292 cases of childhood (0-14 years) ALL, newly diagnosed across Greece over a 4.5 year period as well as for 294 hospital controls. Allergen-specific-IgEs, as markers of allergic predisposition, against 24 most prevalent respiratory and food allergens, were determined, using an enzyme immunoassay procedure for 199 children with ALL and 113 controls. Cases were compared with controls through frequency distributions and unconditional multiple logistic regression models to estimate odds ratios (ORs) and 95% confidence-intervals (CIs) regarding associations of allergy with childhood ALL.

RESULTS

Self-reported-allergic history overall (OR: 0.49, 95% CI: 0.34-0.72) and practically each one of its main components (respiratory, food, any other clinical allergy) were strongly and inversely associated with ALL. Likewise, the serum IgE inverse association was of the same magnitude (OR: 0.43, 95% CI: 0.22-0.84) mainly contributed by food IgE (OR: 0.39, 95% CI: 0.18-0.83).

CONCLUSION

Beyond the already established inverse association of allergic history with childhood ALL, a same magnitude association is evident when serologic markers of allergic predisposition are used as an alternative measure of allergy. Further research with more appropriate study designs is needed to better understand possible associations between prior allergy and childhood ALL risk.

Effects of residential indoor air quality and household ventilation on preterm birth and term low birth weight in Los Angeles County, California

OBJECTIVES

The purpose of our study was to examine the effects of indoor residential air quality on preterm birth and term low birth weight (LBW).

METHODS

We evaluated 1761 nonsmoking women from a case-control survey of mothers who delivered a baby in 2003 in Los Angeles County, California. In multinomial logistic regression models adjusted for maternal age, education, race/ethnicity, parity and birthplace, we evaluated the effects of living with smokers or using personal or household products that may contain volatile organic compounds and examined the influence of household ventilation.

RESULTS

Compared with unexposed mothers, women exposed to secondhand smoke (SHS) at home had increased odds of term LBW (adjusted odds ratio [OR] = 1.36; 95% confidence interval [CI] =  0.85, 2.18) and preterm birth (adjusted OR = 1.27; 95% CI = 0.95, 1.70), although 95% CIs included the null. No increase in risk was observed for SHS-exposed mothers reporting moderate or high window ventilation. Associations were also observed for product usage, but only for women reporting low or no window ventilation.

CONCLUSIONS

Residential window ventilation may mitigate the effects of indoor air pollution among pregnant women in Los Angeles County, California.

Assessing the influence of traffic-related air pollution on risk of term low birth weight on the basis of land-use-based regression models and measures of air toxics

Few studies have examined associations of birth outcomes with toxic air pollutants (air toxics) in traffic exhaust. This study included 8,181 term low birth weight (LBW) children and 370,922 term normal-weight children born between January 1, 1995, and December 31, 2006, to women residing within 5 miles (8 km) of an air toxics monitoring station in Los Angeles County, California. Additionally, land-use-based regression (LUR)-modeled estimates of levels of nitric oxide, nitrogen dioxide, and nitrogen oxides were used to assess the influence of small-area variations in traffic pollution. The authors examined associations with term LBW (≥37 weeks' completed gestation and birth weight <2,500 g) using logistic regression adjusted for maternal age, race/ethnicity, education, parity, infant gestational age, and gestational age squared. Odds of term LBW increased 2%-5% (95% confidence intervals ranged from 1.00 to 1.09) per interquartile-range increase in LUR-modeled estimates and monitoring-based air toxics exposure estimates in the entire pregnancy, the third trimester, and the last month of pregnancy. Models stratified by monitoring station (to investigate air toxics associations based solely on temporal variations) resulted in 2%-5% increased odds per interquartile-range increase in third-trimester benzene, toluene, ethyl benzene, and xylene exposures, with some confidence intervals containing the null value. This analysis highlights the importance of both spatial and temporal contributions to air pollution in epidemiologic birth outcome studies.

Current understanding of the mechanism of benzene-induced leukemia in humans: implications for risk assessment

Benzene causes acute myeloid leukemia and probably other hematological malignancies. As benzene also causes hematotoxicity even in workers exposed to levels below the US permissible occupational exposure limit of 1 part per million, further assessment of the health risks associated with its exposure, particularly at low levels, is needed. Here, we describe the probable mechanism by which benzene induces leukemia involving the targeting of critical genes and pathways through the induction of genetic, chromosomal or epigenetic abnormalities and genomic instability, in a hematopoietic stem cell (HSC); stromal cell dysregulation; apoptosis of HSCs and stromal cells and altered proliferation and differentiation of HSCs. These effects modulated by benzene-induced oxidative stress, aryl hydrocarbon receptor dysregulation and reduced immunosurveillance, lead to the generation of leukemic stem cells and subsequent clonal evolution to leukemia. A mode of action (MOA) approach to the risk assessment of benzene was recently proposed. This approach is limited, however, by the challenges of defining a simple stochastic MOA of benzene-induced leukemogenesis and of identifying relevant and quantifiable parameters associated with potential key events. An alternative risk assessment approach is the application of toxicogenomics and systems biology in human populations, animals and in vitro models of the HSC stem cell niche, exposed to a range of levels of benzene. These approaches will inform our understanding of the mechanisms of benzene toxicity and identify additional biomarkers of exposure, early effect and susceptibility useful for risk assessment.

Assessment of xenobiotic biotransformation including reactive oxygen species generation in the embryo using benzene as an example

Quantification of embryonic metabolic capacity is an important tool in developmental toxicology research. Bioactivation of xenobiotics into reactive intermediates often contributes to embryo toxicity; thus, identification and quantification of these toxic metabolites is essential to gain further understanding of developmental toxicity. This chapter uses the environmental chemical benzene as a model xenobiotic to describe the detection of both metabolites and reactive oxygen species (ROS) in fetal liver. Briefly, mice are bred and the presence of a vaginal plug in a female mouse indicates gestational day 1. On the desired gestational day, pregnant dams are exposed to benzene followed by sacrifice at the desired time-point after exposure. Using gas chromatography coupled to mass spectrometry, the detection of benzene metabolites can be achieved. Additionally, we describe the measurement of ROS by flow cytometry using the fluorescent probe 5-(and-6)-chloromethyl-2',7'-dichlorofluorescein diacetate, which readily diffuses into cells and, upon oxidation by any ROS, is converted to the highly fluorescent, negatively charged carboxydichlorofluorescein, which remains trapped within the cells.

Genome-wide functional profiling reveals genes required for tolerance to benzene metabolites in yeast

Benzene is a ubiquitous environmental contaminant and is widely used in industry. Exposure to benzene causes a number of serious health problems, including blood disorders and leukemia. Benzene undergoes complex metabolism in humans, making mechanistic determination of benzene toxicity difficult. We used a functional genomics approach to identify the genes that modulate the cellular toxicity of three of the phenolic metabolites of benzene, hydroquinone (HQ), catechol (CAT) and 1,2,4-benzenetriol (BT), in the model eukaryote Saccharomyces cerevisiae. Benzene metabolites generate oxidative and cytoskeletal stress, and tolerance requires correct regulation of iron homeostasis and the vacuolar ATPase. We have identified a conserved bZIP transcription factor, Yap3p, as important for a HQ-specific response pathway, as well as two genes that encode putative NAD(P)H:quinone oxidoreductases, PST2 and YCP4. Many of the yeast genes identified have human orthologs that may modulate human benzene toxicity in a similar manner and could play a role in benzene exposure-related disease.

Germline mutation rates in mice following in utero exposure to diesel exhaust particles by maternal inhalation

The induction of inherited DNA sequence mutations arising in the germline (i.e., sperm or egg) of mice exposed in utero to diesel exhaust particles (DEPs) via maternal inhalation compared to unexposed controls was investigated in this study. Previous work has shown that particulate air pollutants (PAPs) from industrial environments cause DNA damage and mutations in the sperm of adult male mice. Effects on the female and male germline during critical stages of development (in utero) are unknown. In mice, previous studies have shown that expanded simple tandem repeat (ESTR) loci exhibit high rates of spontaneous mutation, making this endpoint a valuable tool for studying inherited mutation and genomic instability. In the present study, pregnant C57Bl/6 mice were exposed to 19mg/m(3) DEP from gestational day 7 through 19, alongside air exposed controls. Male and female F1 offspring were raised to maturity and mated with control CBA mice. The F2 descendents were collected and ESTR germline mutation rates were derived from full pedigrees (mother, father, offspring) of F1 male and female mice. We found no evidence for increased ESTR mutation rates in females exposed in utero to DEP relative to control females. In contrast, a statistically significant increase in the mutation frequency of male mice exposed in utero to DEP was observed (2-fold; Fisher's exact p<0.05). Thus, maternal exposure to DEP results in increased mutation in sperm during development.

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.

Transplacental benzene exposure increases tumor incidence in mouse offspring: possible role of fetal benzene metabolism

Childhood cancer is the leading cause of disease-related death in children aged 1-14 years in Canada and the USA and it has been hypothesized that transplacental exposure to environmental carcinogens such as benzene may contribute to the etiology of these cancers. Our objectives were to determine if transplacental benzene exposure increased tumor incidence in mouse offspring and assess fetal benzene metabolism capability. Pregnant CD-1 and C57Bl/6N mice were given intraperitoneal injections of corn oil, 200 mg/kg, or 400 mg/kg benzene on gestational days 8, 10, 12 and 14. A significant increase in tumor incidence was observed in CD-1, but not C57BL/6N, 1-year-old offspring exposed transplacentally to 200 mg/kg benzene. Hepatic and hematopoietic tumors were predominantly observed in male and female CD-1 offspring, respectively. Female CD-1 offspring exposed transplacentally to 200 mg/kg benzene had significantly suppressed bone marrow CD11b(+) cells 1 year after birth, correlating with reduced colony-forming unit granulocyte/macrophage numbers in 2-day-old pups. CD-1 and C57Bl/6N maternal blood benzene levels and fetal liver benzene, t, t-muconic acid, hydroquinone and catechol levels were analyzed by gas chromatography/mass spectrometry. Significant strain-, gender- and dose-related differences were observed. Male CD-1 fetuses had high hydroquinone levels, whereas females had high catechol levels after maternal exposure to 200 mg/kg benzene. This is the first demonstration that transplacental benzene exposure can induce hepatic and hematopoietic tumors in mice, which may be dependent on fetal benzene metabolism capability.

Advances in understanding benzene health effects and susceptibility

Benzene is a ubiquitous chemical in our environment that causes acute leukemia and probably other hematological cancers. Evidence for an association with childhood leukemia is growing. Exposure to benzene can lead to multiple alterations that contribute to the leukemogenic process, indicating a multimodal mechanism of action. Research is needed to elucidate the different roles of multiple metabolites in benzene toxicity and the pathways that lead to their formation. Studies to date have identified a number of polymorphisms in candidate genes that confer susceptibility to benzene hematotoxicity. However, a genome-wide study is needed to truly assess the role of genetic variation in susceptibility. Benzene affects the blood-forming system at low levels of occupational exposure, and there is no evidence of a threshold. There is probably no safe level of exposure to benzene, and all exposures constitute some risk in a linear, if not supralinear, and additive fashion.

Benzene-initiated oxidative stress: Effects on embryonic signaling pathways

Approximately 90% of childhood cancers are of unknown etiology; however, it is hypothesized that in utero carcinogen exposure may contribute. Epidemiological studies have correlated parental exposure to benzene with an increased incidence of childhood leukemias. However, mechanisms of benzene-induced carcinogenesis following in utero exposure remain unknown. We hypothesize that in utero exposure to benzene causes alterations in the redox-sensitive signaling pathways involving c-Myb, Pim-1, AKT, ERK-MAPK, p38-MAPK, and NF-kappaB via the production of reactive oxygen species (ROS) as a possible mechanism of in utero-initiated carcinogenesis. Using a CD-1 mouse model we have shown increased oxidative stress in fetal tissue from embryos exposed in utero to benzene by measuring reduced to oxidized glutathione ratios, and increased levels of ROS in male fetuses using flow cytometry and the ROS sensitive fluorescent probe dichlorofluoroscein diacetate (DCFDA). In addition, using Western blotting techniques we observed increased expression of fetal Pim-1, Pim-1 phosphorylation, c-Myb, and phosphorylated p38-MAPK (activated form) and lower protein levels of IkappaBalpha, while phosphorylated ERK-MAPK and AKT protein levels did not change. Interestingly, we found male fetuses more susceptible to benzene-induced oxidative stress, which is in agreement with the literature suggesting that males are more susceptible to benzene toxicity. Further studies evaluating the reason for this gender difference are ongoing.