The effects of Nrf2 knockout on regulation of benzene-induced mouse hematotoxicity

Risk assessment of Benzene, Toluene, Ethyl benzene, and Xylene (BTEX) in the atmospheric air around the world: A review

Volatile organic compounds, such as BTEX, have been the subject of numerous debates due to their detrimental effects on the environment and human health. Human beings have had a significant role in the emergence of this situation. Even though US EPA, WHO, and other health-related organizations have set standard limits as unhazardous levels, it has been observed that within or even below these limits, constant exposure to these toxic chemicals results in negative consequences as well. According to these facts, various studies have been carried out all over the world - 160 of which are collected within this review article, so that experts and governors may come up with effective solutions to manage and control these toxic chemicals. The outcome of this study will serve the society to evaluate and handle the risks of being exposed to BTEX. In this review article, the attempt was to collect the most accessible studies relevant to risk assessment of BTEX in the atmosphere, and for the article to contain least bias, it was reviewed and re-evaluated by all authors, who are from different institutions and backgrounds, so that the insights of the article remain unbiased. There may be some limitations to consistency or precision in some points due to the original sources, however the attempt was to minimize them as much as possible.

8-OHdG mediates the association of co-exposure to fifty-five typical endocrine-disrupting chemicals with renal function: a cross-section investigation in Southern Chinese adults

Individual typical endocrine-disrupting chemicals (EDCs), including organophosphate triesters (OPEs), parabens, triclosan (TCS), bisphenols, benzophenones (BPs), phthalates (PAEs), and synthetic phenolic antioxidants (SPAs), are associated with renal dysfunction. However, the combined effects and underlying mechanisms of mixed EDC exposure on renal function remain unclear. Two hundred ninety-nine adult participants were enrolled in the cross-sectional survey conducted in Guangzhou, China. Urinary levels of 7 OPEs, 6 parabens, TCS, 14 bisphenols, 8 BPs, 15 PAEs, 4 SPAs, and 8-hydroxy-2'-deoxyguanosine (8-OHdG) were determined, and estimated glomerular filtration rate (eGFR) was served as the outcome index. We found elevated levels of diphenyl phosphate (DPP), bisphenol A (BPA), mono-(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP), and mono-butyl phthalate (MBP) showed dose-responsive associations with eGFR decline, However, nonlinear associations were observed for bis(2-butoxyethyl) hydrogen phosphate (BBOEP), TCS, 4-hydroxybenzophenone (HBP), mono-n-pentyl phthalate (MnPP), and mono-benzyl phthalate (MBzP). The quantile-based g-computation model demonstrated that a quartile increase in the EDC mixture corresponded to a 0.383-SD decrease (95% CI - 0.658 ~  - 0.108, P = 0.007) in eGFR. Notably, BPA was identified as the primary contributor to this effect. Moreover, 8-OHdG mediated the eGFR decline associated with EDC mixtures with a mediation proportion of 25.49%. A sex-modified effect was also observed (P = 0.004), indicating that exposure to the mixture of EDC was linked to more pronounced renal dysfunction in females. Our novel findings suggest that exposure to a typical mixture of EDCs is associated with renal dysfunction in the general adult population of Southern China. Furthermore, 8-OHdG may play a role in the pathogenesis of EDC mixture-related renal dysfunction.

Study on the underlying molecular mechanism of benzene-induced nervous system damage in mice based on tandem mass tag (TMT) proteomics

Benzene is known to be a common toxic industrial chemical, and prolonged benzene exposure may cause nervous system damage. At present, there were few studies on benzene-induced neurological damage. This research aimed to identify the protein biomarkers to explore the mechanism of nervous system damage caused by benzene. We established a benzene poisoning model of C57 mice by gavage of benzene-peanut oil suspension and identified differentially expressed proteins (DEPs) in brain tissue using tandem mass tag (TMT) proteomics. The results showed a significant weight loss and decrease in leukocyte and neutrophil counts in benzene poisoning mice compared to the control group. We also observed local cerebral oedema and small vessel occlusion in the cerebral white matter of benzene poisoning mice. TMT proteomic results showed that a total 6,985 proteins were quantified, with a fold change (FC) > 1.2 (or < 1/1.2) and P value <0.05 were considered as DEPs. Compared with the control group, we identified 43 DEPs, comprising 14 upregulated and 29 downregulated proteins. Kyoto encyclopedia of genes and genomes (KEGG) pathway analysis results showed that the candidate proteins were mainly involved in cholesterol metabolism, complement and coagulation cascades, african trypanosomiasis, PPAR signaling pathway, and vitamin digestion and absorption. Three proteins, 2-hydroxyacylsphingosine 1-beta-galactosyltransferase (UGT8), Apolipoprotein A-I (APOA1) and Complement C3 (C3) were validated using immunoblotting and immunohistochemical. In conclusion, our study preliminarily investigated the mechanism of benzene toxicity to the nervous system by analyzing DEPs changes in the brain.

Interventional probability of causation (IPoC) with epidemiological and partial mechanistic evidence: benzene vs. formaldehyde and acute myeloid leukemia (AML)

INTRODUCTION

Causal epidemiology for regulatory risk analysis seeks to evaluate how removing or reducing exposures would change disease occurrence rates. We define interventional probability of causation (IPoC) as the change in probability of a disease (or other harm) occurring over a lifetime or other specified time interval that would be caused by a specified change in exposure, as predicted by a fully specified causal model. We define the closely related concept of causal assigned share (CAS) as the predicted fraction of disease risk that would be removed or prevented by a specified reduction in exposure, holding other variables fixed. Traditional approaches used to evaluate the preventable risk implications of epidemiological associations, including population attributable fraction (PAF) and the Bradford Hill considerations, cannot reveal whether removing a risk factor would reduce disease incidence. We argue that modern formal causal models coupled with causal artificial intelligence (CAI) and realistically partial and imperfect knowledge of underlying disease mechanisms, show great promise for determining and quantifying IPoC and CAS for exposures and diseases of practical interest.

METHODS

We briefly review key CAI concepts and terms and then apply them to define IPoC and CAS. We present steps to quantify IPoC using a fully specified causal Bayesian network (BN) model. Useful bounds for quantitative IPoC and CAS calculations are derived for a two-stage clonal expansion (TSCE) model for carcinogenesis and illustrated by applying them to benzene and formaldehyde based on available epidemiological and partial mechanistic evidence.

RESULTS

Causal BN models for benzene and risk of acute myeloid leukemia (AML) incorporating mechanistic, toxicological and epidemiological findings show that prolonged high-intensity exposure to benzene can increase risk of AML (IPoC of up to 7e-5, CAS of up to 54%). By contrast, no causal pathway leading from formaldehyde exposure to increased risk of AML was identified, consistent with much previous mechanistic, toxicological and epidemiological evidence; therefore, the IPoC and CAS for formaldehyde-induced AML are likely to be zero.

CONCLUSION

We conclude that the IPoC approach can differentiate between likely and unlikely causal factors and can provide useful upper bounds for IPoC and CAS for some exposures and diseases of practical importance. For causal factors, IPoC can help to estimate the quantitative impacts on health risks of reducing exposures, even in situations where mechanistic evidence is realistically incomplete and individual-level exposure-response parameters are uncertain. This illustrates the strength that can be gained for causal inference by using causal models to generate testable hypotheses and then obtaining toxicological data to test the hypotheses implied by the models-and, where necessary, refine the models. This virtuous cycle provides additional insight into causal determinations that may not be available from weight-of-evidence considerations alone.

Oxidative stress-affected ACSL1 hydroxymethylation triggered benzene hematopoietic toxicity by inflammation and senescence

Long-term benzene exposure is harmful and causes hematopoietic dysfunction. However, the mechanism of benzene hematopoietic toxicity is still unclear. Acyl-CoA Synthetase Long-Chain Family Member 1 (ACSL1) has been found to participate in the progress of a variety of benign and malignant diseases, but there is no research about its effect on benzene-induced hematopoietic toxicity. Herein, We exposed C57BL/6J mice to benzene to construct an in vivo model. Human peripheral blood mononuclear cells (THP-1 cells) were treated with benzene metabolite 1, 4-BQ to construct an in vitro model. We observed that the ACSL1 expression was upregulated both in vivo and in vitro. Moreover, inhibition of ACSL1 relieved inflammation and senescence development in vitro, suggesting that ACSL1 mediates inflammation and senescence. As for the regulation mechanism of ACSL1 expression, it is closely related to hydroxymethylation modification. This was proved by hydroxymethylated DNA immunoprecipitation (hMeDIP) experiments. Furthermore, oxidative stress influenced the hydroxymethylation process. These results showed that benzene hematopoietic toxicity occurs through the induction of oxidative stress and thus the regulation of ACSL1 hydroxymethylation, which in turn mediates inflammation and senescence. Thus, this study might be of great significance in identifying and preventing benzene exposure in the early stage.

PM2.5 Increases Systemic Inflammatory Cells and Associated Disease Risks by Inducing NRF2-Dependent Myeloid-Biased Hematopoiesis in Adult Male Mice

Although PM_2.5 (fine particles with aerodynamic diameter <2.5 μm) exposure shows the potential to impact normal hematopoiesis, the detailed alterations in systemic hematopoiesis and the underlying mechanisms remain unclear. For hematopoiesis under steady-state or stress conditions, nuclear factor erythroid 2-related factor 2 (NRF2) is essential for regulating hematopoietic processes to maintain blood homeostasis. Herein, we characterized changes in the populations of hematopoietic stem progenitor cells and committed hematopoietic progenitors in the lungs and bone marrow (BM) of wild-type and Nrf2^-/- C57BL/6J male mice. PM_2.5-induced NRF2-dependent biased hematopoiesis toward myeloid lineage in the lungs and BM generates excessive numbers of various inflammatory immune cells, including neutrophils, monocytes, and platelets. The increased population of these immune cells in the lungs, BM, and peripheral blood has been associated with observed pulmonary fibrosis and high disease risks in an NRF2-dependent manner. Therefore, although NRF2 is a protective factor against stressors, upon PM_2.5 exposure, NRF2 is involved in stress myelopoiesis and enhanced PM_2.5 toxicity in pulmonary injury, even leading to systemic inflammation.

Curcumin attenuates AFB1-induced duck liver injury by inhibiting oxidative stress and lysosomal damage

Aflatoxin B1 (AFB1), as the most toxic secondary metabolite produced by Aspergillus flavus, is a serious threat to human and animal health. Curcumin, a polyphenol from the plant turmeric, has demonstrated unique anti-damage properties in several studies. But, its ability to alleviate AFB1-induced liver damage in ducks and the underlying mechanisms are not completely elucidated. In this study, we investigated the intervention of curcumin on AFB1-induced hepatotoxicity in ducks. Research data showed that the combination of curcumin and AFB1 alleviated oxidative stress, reduced malondialdehyde (MDA) accumulation and relieved hepatotoxicity after 28 days of treatment, compared with AFB1. Also, curcumin upregulated the expression of nuclear factor erythroid 2-related factor 2 (Nrf2) and its downstream antioxidant enzymes (SOD, HO-1), which enhanced the antioxidant capacity of the liver. In addition, curcumin inhibited AFB1-induced lysosomal damage in the liver, with the character of reduced lysosomal membrane permeabilization, restored autophagic flux, and promoted lysosomal biogenesis, thereby enhancing the self-protective capacity of the liver. In conclusion, our results suggest that curcumin alleviates AFB1-induced duck hepatotoxicity by inhibiting oxidative stress and lysosomal damage.

Assessment of health risk and dose-effect of DNA oxidative damage for the thirty chemicals mixture of parabens, triclosan, benzophenones, and phthalate esters

Humans are constantly exposed to parabens (PBs), triclosan (TCS), benzophenones (BPs), and phthalate esters (PAEs) due to the widespread existence of these chemicals in personal care products (PCPs), and the high frequency of usage for humans. Previous studies indicated each class of the above-mentioned chemicals can exhibit potential adverse effects on humans, in particular DNA oxidative damage. However, the health risk assessment of combined exposures to multiple PCPs is limited, especially the overall dose-effect of mixtures of these chemicals on DNA oxidative damage. In this study, we measured the urinary levels of 6 PBs, TCS, 8 BPs, 15 metabolites of PAEs (mono-PAEs), and 8-hydroxy-2'-deoxyguanosine (8-OHdG) from 299 adults simultaneously. PBs, TCS, BPs, and mono-PAEs were frequently detected in urinary samples with median concentrations of 52.888, 0.737, 1.305, and 141.381 ng/ml, suggesting a broad, low-level exposure among participants. Risk assessments indicated approximately 22% and 15% of participants suffered health risks (Hazard index >1) from exposure to TCS and PAEs. The relationship between 8-OHdG levels and chemical exposure was estimated by Bayesian kernel machine regression (BKMR) models. It indicated an overall positive correlation between the mixture of these chemicals and 8-OHdG, with methylparaben and mono-benzyl phthalate contributing the most to this association. Of note, sex-related differences were observed, in which exposure to PCPs led to higher health risks and more pronounced dose-effect on DNA damage in the female population. Our novel findings reveal the health risks of exposure to low-level PCPs mixtures and further point out the overall dose-response relationship between DNA oxidative damage and PCP mixtures.

Iron-dependent ferroptosis participated in benzene-induced anemia of inflammation through IRP1-DHODH-ALOX12 axis

Benzene, a widely existing environmental pollutant, gives huge harm to the hematopoietic system. Iron is one of the raw materials for the creation of blood cells, but the role of iron in the blood toxicity of benzene is still unknown. Here, we examined the role of iron homeostasis in benzene-induced toxicity both in vivo and in vitro. In this study, mice exposed to benzene at 50 ppm for 8 weeks demonstrated the anemia of inflammation, mainly manifested as the decreased serum Fe²⁺, increased serum ferritin and inflammation factors (TNF-α, IL6, IL1β) in the plasma of mice. Furthermore, we found that iron maldistribution in the spleen and bone marrow is accompanied by inflammation reaction and ferroptosis. In the vitro study, benzene metabolite 1,4-BQ stimulated the obvious ROS production and ferroptosis activation in the normal B lymphocytes cells. Meanwhile, from the molecular perspective, the combined proteomics and transcriptome enriched the ferroptosis pathway, and we further confirmed the increased expression of iron regulator IRP1, ferroptosis-regulator DHODH, and fatty acids metabolism enzyme ALOX12 were the crucial participators in regulating benzene-mediated iron metabolism imbalance and ferroptosis. Particularly, the targeted and un-targeted metabolomics in the vivo and vitro study further emphasized the importance of DHODH in benzene-induced ferroptosis. In conclusion, this study revealed that iron-dependent ferroptosis participated in benzene-induced anemia of inflammation and provided a constructive perspective on targeting ferroptosis for the prevention and control of benzene toxicity.

ROS-directed activation of Toll/NF-κB in the hematopoietic niche triggers benzene-induced emergency hematopoiesis

Hematopoietic stem cells/progenitor cells (HSC/HPCs) orchestrate the hematopoietic process, effectively regulated by the hematopoietic niche under normal and stressed conditions. The hematopoietic niche provides various soluble factors which influence the differentiation and self-renewal of HSC/HSPs. Unceasing differentiation/proliferation/high metabolic activity of HSC/HPCs makes them susceptible to damage by environmental toxicants like benzene. Oxidative stress, epigenetic modifications, and DNA damage in the HSC/HPCs are the key factors of benzene-induced hematopoietic injury. However, the role of the hematopoietic niche in benzene-induced hematopoietic injury/response is still void. Therefore, the current study aims to unravel the role of the hematopoietic niche in benzene-induced hematotoxicity using a genetically tractable model, Drosophila melanogaster. The lymph gland is a dedicated hematopoietic organ in Drosophila larvae. A group of 30-45 cells called the posterior signaling center (PSC) in the lymph gland acts as a niche that regulates Drosophila HSC/HPCs maintenance. Benzene exposure to Drosophila larvae (48 h) resulted in aberrant hemocyte production, especially hyper-differentiation of lamellocytes followed by premature lymph gland dispersal and reduced adult emergence upon developmental exposure. Subsequent genetic experiments revealed that benzene-induced lamellocyte production and premature lymph gland dispersal were PSC mediated. The genetic experiments further showed that benzene generates Dual oxidase (Duox)-dependent Reactive Oxygen Species (ROS) in the PSC, activating Toll/NF-κB signaling, which is essential for the aberrant hemocyte production, lymph gland dispersal, and larval survival. Together, the study establishes a functional perspective of the hematopoietic niche in a benzene-induced hematopoietic emergency in a genetic model, Drosophila, which might be relevant to higher organisms.

Effects of Benzene: Hematological and Hypersensitivity Manifestations in Resident Living in Oil Refinery Areas

Literature is teeming with publications on industrial pollution. Over the decades, the main industrial pollutants and their effects on human health have been widely framed. Among the various compounds involved, benzene plays a leading role in the onset of specific diseases. Two systems are mainly affected by the adverse health effects of benzene exposure, both acute and chronic: the respiratory and hematopoietic systems. The most suitable population targets for a proper damage assessment on these systems are oil refinery workers and residents near refining plants. Our work fits into this area of interest with the aim of reviewing the most relevant cases published in the literature related to the impairment of the aforementioned systems following benzene exposure. We perform an initial debate between the two clinical branches that see a high epidemiological expression in this slice of the population examined: residents near petroleum refinery areas worldwide. In addition, the discussion expands on highlighting the main immunological implications of benzene exposure, finding a common pathophysiological denominator in inflammation, oxidative stress, and DNA damage, thus helping to set the basis for an increasingly detailed characterization aimed at identifying common molecular patterns between the two clinical fields discussed.

Benzene Exposure Leads to Lipodystrophy and Alters Endocrine Activity In Vivo and In Vitro

Benzene is a ubiquitous pollutant and mainly accumulates in adipose tissue which has important roles in metabolic diseases. The latest studies reported that benzene exposure was associated with many metabolic disorders, while the effect of benzene exposure on adipose tissue remains unclear. We sought to investigate the effect using in vivo and in vitro experiments. Male adult C57BL/6J mice were exposed to benzene at 0, 1, 10 and 100 mg/kg body weight by intragastric gavage for 4 weeks. Mature adipocytes from 3T3-L1 cells were exposed to hydroquinone (HQ) at 0, 1, 5 and 25 μM for 24 hours. Besides the routine hematotoxicity, animal experiments also displayed significant body fat content decrease from 1 mg/kg. Interestingly, the circulating non-esterified fatty acid (NEFA) level increased from the lowest dose (p_trend < 0.05). Subsequent analysis indicated that body fat content decrease may be due to atrophy of white adipose tissue (WAT) upon benzene exposure. The average adipocyte area of WAT decreased significantly even from 1 mg/kg with no significant changes in total number of adipocytes. The percentages of small and large adipocytes in WAT began to significantly increase or decrease from 1 mg/kg (all p < 0.05), respectively. Critical genes involved in lipogenesis and lipolysis were dysregulated, which may account for the disruption of lipid homeostasis. The endocrine function of WAT was also disordered, manifested as significant decrease in adipokine levels, especially the leptin. In vitro cell experiments displayed similar findings in decreased fat content, dysregulated critical lipid metabolism genes, and disturbed endocrine function of adipocytes after HQ treatment. Pearson correlation analysis showed positive correlations between white blood cell (WBC) count with WAT fat content and plasma leptin level (r = 0.330, 0.344, both p < 0.05). This study shed light on the novel aspect that benzene exposure could induce lipodystrophy and disturb endocrine function of WAT, and the altered physiology of WAT might in turn affect benzene-induced hematotoxicity and metabolic disorders. The study provided new insight into understanding benzene-induced toxicity and the relationship between benzene and adipose tissue.

The effects of glucose-6-phosphate dehydrogenase deficiency on benzene-induced hematotoxicity in mice

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most common human enzyme deficiency. Our previous study revealed the level of G6PD changed in wild type (WT) mice after benzene exposure. In this study, the pentose phosphate pathway (PPP) in regulation of benzene-induced hematotoxicity was investigated and other potential pathways were discovered in a G6PD deficiency mouse model. WT and G6PD mutation (G6PD^mut) mice were exposed to benzene (diluted in corn oil) at doses of 0 and 160 mg/kg by subcutaneous injection for 5 days/week, 4 weeks. Peripheral blood samples and bone marrow cells (BMCs) were obtained and measured. The levels of nicotinamide adenine dinucleotide phosphate (NADPH),reduced glutathione (GSH) and malondialdehyde (MDA) were detected and comet assay was analyzed for DNA damage in BMCs. Finally, RNA sequencing (RNA-seq) of BMCs was performed. The results showed that white blood cells decreased significantly in G6PD^mut mice compared with WT mice after benzene treatment. The ratio of hematopoietic stem/progenitor cells significantly decreased in G6PD^mut mice exposed to benzene. The reduction of NADPH and GSH revealed the effect on PPP with G6PD deficiency, which then caused the increase of MDA and DNA damage. Finally, RNA-seq results suggested potential genes including SHROOM4, CAMK2B and REN1 played potential roles of G6PD deficiency on benzene-induced hematotoxicity. Renin-angiotensin system and cAMP signaling pathway were potentially involved in the process. Our study provides a better understanding for the effects of G6PD deficiency on benzene-induced hematotoxicity.

Exposure to a mixture of 23 chemicals associated with unconventional oil and gas operations alters immune response to challenge in adult mice

The prevalence of unconventional oil and gas (UOG) operations raises concerns regarding the potential for adverse health outcomes following exposure to water tainted by mixtures of UOG associated chemicals. The potential effects that exposure to complex chemical mixtures has on the immune system have yet to be fully evaluated. In this study, effects on the immune system of adult mice exposed to a mixture of 23 chemicals that have been associated with water near active UOG operations were investigated. Female and male mice were exposed to the mixture via their drinking water for at least 8 weeks. At the end of the exposure, cellularity of primary and secondary immune organs, as well as an immune system function, were assessed using three different models of disease, i.e. house dust mite (HDM)-induced allergic airway disease, influenza A virus infection, and experimental autoimmune encephalomyelitis (EAE). The results indicated exposures resulted in different impacts on T-cell populations in each disease model. Furthermore, the consequences of exposure differed between female and male mice. Notably, exposure to the chemical mixture significantly increased EAE disease severity in females, but not in male, mice. These findings indicated that direct exposure to this mixture leads to multiple alterations in T-cell subsets and that these alterations differ between sexes. This suggested to us that direct exposure to UOG-associated chemicals may alter the adult immune system, leading to dysregulation in immune cellularity and function.

Quercetin and Isorhamnetin Attenuate Benzo[a]pyrene-Induced Toxicity by Modulating Detoxification Enzymes through the AhR and NRF2 Signaling Pathways

Benzo[a]pyrene, classified as a Group 1 carcinogen, is metabolized to B[a]P-7,8-dihydrodiol-9,10-epoxide (BPDE), causing DNA mutations and eventually cancer. Quercetin is a dietary flavonoid abundant in fruits and vegetables. After quercetin intake, quercetin's metabolites isorhamnetin and miquelianin are more highly concentrated than quercetin in the human plasma. In this study, we investigated the molecular mechanisms associated with the cytoprotective effect of quercetin and its metabolites against benzo[a]pyrene from a detoxification perspective. Quercetin and its metabolite isorhamnetin reduced benzo[a]pyrene-induced cytotoxicity, whereas the metabolite miquelianin did not mitigate benzo[a]pyrene-induced cytotoxicity. Moreover, quercetin and isorhamnetin reduced intracellular levels of BPDE-DNA adducts. The formation and elimination of BPDE is mediated by the xenobiotic detoxification process. Quercetin and isorhamnetin increased the gene and protein expression levels of phase I, II, and III enzymes involved in xenobiotic detoxification. Furthermore, quercetin and isorhamnetin induced the translocation of aryl hydrocarbon receptor (AhR) and nuclear factor erythroid 2-related factor 2 (NRF2), which regulate the expression level of phase enzymes. Our results suggest that quercetin and isorhamnetin promote the metabolism, detoxification, and elimination of B[a]P, thereby increasing anti-genotoxic effects and protecting against B[a]P-induced cytotoxicity.

Utility of a next generation framework for assessment of genomic damage: A case study using the industrial chemical benzene

We recently published a next generation framework for assessing the risk of genomic damage via exposure to chemical substances. The framework entails a systematic approach with the aim to quantify risk levels for substances that induce genomic damage contributing to human adverse health outcomes. Here, we evaluated the utility of the framework for assessing the risk for industrial chemicals, using the case of benzene. Benzene is a well-studied substance that is generally considered a genotoxic carcinogen and is known to cause leukemia. The case study limits its focus on occupational and general population health as it relates to benzene exposure. Using the framework as guidance, available data on benzene considered relevant for assessment of genetic damage were collected. Based on these data, we were able to conduct quantitative analyses for relevant data sets to estimate acceptable exposure levels and to characterize the risk of genetic damage. Key observations include the need for robust exposure assessments, the importance of information on toxicokinetic properties, and the benefits of cheminformatics. The framework points to the need for further improvement on understanding of the mechanism(s) of action involved, which would also provide support for the use of targeted tests rather than a prescribed set of assays. Overall, this case study demonstrates the utility of the next generation framework to quantitatively model human risk on the basis of genetic damage, thereby enabling a new, innovative risk assessment concept. Environ. Mol. Mutagen. 61:94-113, 2020. © 2019 The Authors. Environmental and Molecular Mutagenesis published by Wiley Periodicals, Inc. on behalf of Environmental Mutagen Society.

Reactive Oxygen Species and Nrf2: Functional and Transcriptional Regulators of Hematopoiesis

Hematopoietic stem cells (HSCs) are characterized by self-renewal and multilineage differentiation potentials. Although they play a central role in hematopoietic homeostasis and bone marrow (BM) transplantation, they are affected by multiple environmental factors in the BM. Here, we review the effects of reactive oxygen species (ROS) and Nrf2 on HSC function and BM transplantation. HSCs reside in the hypoxic microenvironment of BM, and ROS play an important role in HSPC regulation. Recently, an extraphysiologic oxygen shock/stress phenomenon was identified in human cord blood HSCs collected under ambient air conditions. Moreover, Nrf2 has been recently recognized as a master transcriptional factor that regulates multiple antioxidant enzymes. Since several years, the role of Nrf2 in hematopoiesis has been extensively studied, which has functional similarities of cellular oxygen sensor hypoxia-inducible factor-1 as transcriptional factors. Increasing evidence has revealed that abnormally elevated ROS production due to factors such as genetic defects, aging, and ionizing radiation unexceptionally resulted in lethal impairment of HSC function and hematopoiesis. Both experimental and clinical studies have identified elevated ROS levels as a major culprit of ineffective BM transplantation. Lastly, we discuss the possibility of using small molecule antioxidants, such as N-acetyl cysteine, resveratrol, and curcumin, to augment HSC function and improve the therapeutic efficacy of BM transplantation. Further research on the function of ROS levels and improving the efficacy of BM transplantation may have a great potential for broad clinical applications of HSCs.