Benzene metabolites enhance reactive oxygen species generation in HL60 human leukemia cells

Association of Urinary Benzene Metabolite and the Ratio of Triglycerides to High-Density Lipoprotein Cholesterol: A Cross-Sectional Study Using the Korean National Environmental Health Survey (2018-2020)

The aim of this study was to investigate the association between benzene and toluene, and the ratio of triglycerides to high-density lipoprotein cholesterol (TG/HDL-C). This cross-sectional study analyzed 1928 adults using nationally representative data from the Korean National Environmental Health Survey (KoNEHS) Cycle 4 (2018-2020). Urinary trans, trans-muconic acid (t,t-MA) and benzylmercapturic acid (BMA) were measured by high-performance liquid chromatography-mass spectrometry (HPLC-MS/MS), and high-density lipoprotein cholesterol (HDL-C) and triglycerides (TGs) were analyzed by colorimetry. Survey logistic regression analysis was applied to examine the association between urinary t,t-MA and BMA and the TG/HDL-C ratio. Urinary t,t-MA is significantly associated with an elevated TG/HDL-C ratio in both men and women (for men, OR [95% (CI)]: 2nd quartile: 2.10 [1.04, 4.22]; 3rd quartile: 2.13 [0.98, 4.62]; 4th quartile: 2.39 [1.05, 5.45]; for women, OR [95% (CI)]: 2nd quartile: 1.21 [0.71, 2.06]; 3rd quartile: 1.65 [0.94, 2.90]; 4th quartile: 1.78 [1.01, 3.11]), with significant dose-response relationships (P for trend: for men, 0.029; women, 0.024). This study shows that environmental exposure to benzene is associated with the TG/HDL-C ratio in the Korean general population. This suggests that more stringent environmental health policies are needed to reduce benzene exposure.

Association of metabolites of benzene and toluene with lipid profiles in Korean adults: Korean National Environmental Health Survey (2015-2017)

Background

Environmental exposure to benzene and toluene is a suspected risk factor for metabolic disorders among the general adult population. However, the effects of benzene and toluene on blood lipid profiles remain unclear. In this study, we investigated the association between urinary blood lipid profiles and metabolites of benzene and toluene in Korean adults.

Methods

We analyzed the data of 3,423 adults from the Korean National Environmental Health Survey Cycle 3 (2015–2017). We used urinary trans,trans-muconic acid (ttMA) as a biomarker of benzene exposure, and urinary benzylmercapturic acid (BMA) as an indicator of toluene exposure. Multivariate logistic regression analyses were performed to explore the association between blood lipid profiles and urinary metabolites of benzene and toluene. Additionally, we examined the linear relationship and urinary metabolites of benzene and toluene between lipoprotein ratios using multivariate regression analyses.

Results

After adjusting for covariates, the fourth quartile (Q4) of ttMA [odds ratio (OR) (95% confidence interval, CI = 1.599 (1.231, 2.077)] and Q3 of BMA [OR (95% CI) = 1.579 (1.129, 2.208)] were associated with an increased risk of hypertriglyceridemia. However, the Q4 of urinary ttMA [OR (95% CI) = 0.654 (0.446, 0.961)] and Q3 of urinary BMA [OR (95% CI) = 0.619 (0.430, 0.889)] decreased the risk of a high level of low-density lipoprotein cholesterol (LDL-C). Higher urinary ttMA levels were positively associated with the ratio of triglycerides to high-density lipoproteins [Q4 compared to Q1: β = 0.11, 95% CI: (0.02, 0.20)]. Higher urinary metabolite levels were negatively associated with the ratio of low-density lipoprotein to high-density lipoprotein [Q4 of ttMA compared to reference: β = -0.06, 95% CI: (-0.11, -0.01); Q4 of BMA compared to reference: β = -0.13, 95% CI: (-0.19, -0.08)].

Conclusion

Benzene and toluene metabolites were significantly and positively associated with hypertriglyceridemia. However, urinary ttMA and BMA levels were negatively associated with high LDL-C levels. These findings suggest that environmental exposure to benzene and toluene disrupts lipid metabolism in humans.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12889-022-14319-x.

Combined efficacy of Cinnamomum zeylanicum and doxorubicin against leukemia through regulation of TRAIL and NF-kappa B pathways in rat model

BACKGROUND

Recent discoveries in cancer therapeutics have proven combination therapies more effective than individual drugs. This study describes the efficacy of the combination of Cinnamomum zeylanicum and doxorubicin against benzene-induced leukemia.

METHODS AND RESULTS

Brine shrimp assay was used to assess the cytotoxicity of C. zeylanicum, doxorubicin and their combination. After AML induction in Sprague Dawley rats, the same drugs were given to rat groups. Changes in organ weight, haematological profile, and hepatic enzymes were determined. Real-time PCR was used to elucidate the effect on the expression of STMN1, GAPDH, P53 and various TRAIL and NF-kappaB components. C. zeylanicum reduced the cytotoxicity of doxorubicin. The combination treatment showed better anti-leukemic results than any of the individual drugs as evident from STMN1 expression (p < 0.001). It was particularly effective in reducing total white blood cell counts and recovering lymphocytes, monocytes and eosinophils along with hepatic enzymes ALT and AST (p < 0.001). All doses recovered relative organ weights and improved blood parameters. The combination therapy was particularly effective in inducing apoptosis, inhibition of proliferation marker GAPDH (p < 0.001) and NF-kappaB pathway components Rel-A (p < 0.001) and Rel-B (p < 0.01). Expressions of TRAIL components c-FLIP (p < 0.001), TRAIL ligand (p < 0.001) and caspase 8 (p < 0.01) were also altered.

CONCLUSION

Cinnamomum zeylanicum in combination with doxorubicin helps to counter benzene-induced cellular and hepatic toxicity and improves haematological profile. The anti-leukemic effects are potentially due to inhibition of GAPDH and NF-kappa B pathway, and through regulation of TRAIL pathway. Our data suggests the use of C. zeylanicum with doxorubicin to improve anti-leukemic therapeutic regimes.

Exposure to benzene, toluene and polycyclic aromatic hydrocarbons in Nunavimmiut aged 16 years and over (Nunavik, Canada) - Qanuilirpitaa 2017 survey

There are numerous volatile organic compounds (VOCs) and polycyclic aromatic hydrocarbons (PAHs) that Inuit may be exposed to from combustion, cooking, heating, vehicle exhaust, active and passive smoking and other local sources of contaminants such as oil spills or open-air burning in landfills. To better assess the levels of exposure to these non-persistent chemicals, we measured a suite of benzene, toluene (two VOCs) and PAHs metabolites in pooled urine samples from youth and adults aged 16 years old and over who participated in the Qanuilirpitaa? 2017 Inuit Health Survey (Q2017), a population health survey conducted in Nunavik. A cost-effective pooling strategy was established and 30 different pools from individual urine samples (n = 1266) were created by grouping individual urine samples by sex, age groups and regions. To assess smoking and exposure to second-hand smoke, cotinine levels were measured in individual urine samples. We found that benzene, toluene, all detected PAHs metabolites and cotinine levels were significantly higher in Q2017 compared to adults in the Canadian Health Measure Survey Cycle 4 (2014-2015) or the general U.S population (2015-2016). Moreover, mean levels of one benzene metabolite, S-phenylmercapturic acid, and several PAHs metabolites, 1-naphthol, 2-and 3-hydroxyfluorene, and 4- and 9-hydroxyphenanthrene, known to be associated with smoking habits, were higher in Q2017 compared to reference values (RV₉₅) established for non-smokers in the general Canadian population. Furthermore, benzene and PAHs metabolites were all correlated with cotinine levels. Our results suggest that the high smoking prevalence in Nunavik is an important contributor to the elevated benzene and PAHs exposure. Other local sources may add to that exposure, although we were not able to account for their contribution. These data highlight the importance of regional and community efforts for reducing smoking and to encourage smoke-free homes in Nunavik, while continuing to investigate and reduce other possible local sources of exposure to benzene, toluene and PAHs.

Effect of Environmental Stressors, Xenobiotics, and Oxidative Stress on Male Reproductive and Sexual Health

This article examines the environmental factor-induced oxidative stress (OS) and their effects on male reproductive and sexual health. There are several factors that induce OS, i.e. radition, metal contamination, xenobiotic compounds, and cigarette smoke and lead to cause toxicity in the cells through metabolic or bioenergetic processes. These environmental factors may produce free radicals and enhance the reactive oxygen species (ROS). Free radicals are molecules that include oxygen and disbalance the amount of electrons that can create major chemical chains in the body and cause oxidation. Oxidative damage to cells may impair male fertility and lead to abnormal embryonic development. Moreover, it does not only cause a vast number of health issues such as ageing, cancer, atherosclerosis, insulin resistance, diabetes mellitus, cardiovascular diseases, ischemia-reperfusion injury, and neurodegenerative disorders but also decreases the motility of spermatozoa while increasing sperm DNA damage, impairing sperm mitochondrial membrane lipids and protein kinases. This chapter mainly focuses on the environmental stressors with further discussion on the mechanisms causing congenital impairments due to poor sexual health and transmitting altered signal transduction pathways in male gonadal tissues.

Exposure to polycyclic aromatic hydrocarbons and volatile organic compounds is associated with a risk of obesity and diabetes mellitus among Korean adults: Korean National Environmental Health Survey (KoNEHS) 2015-2017

Environmental pollutants have been known to increase the risks of not only respiratory and cardiovascular disease but also metabolic diseases such as obesity and diabetes mellitus (DM). Polycyclic aromatic hydrocarbons (PAHs) and volatile organic compounds (VOCs) such as benzene and toluene are major constituents of environmental pollution. In the present study, we employed the population of the Korean National Environmental Health Survey (KoNEHS) Cycle 3 conducted between 2015 and 2017, and assessed the associations of urinary biomarkers for PAHs and VOCs exposure with obesity and DM. A total of 3787 adult participants were included and the urinary concentrations of four PAH metabolites and two VOC metabolites were measured. For correcting urine dilution, a covariate-adjusted standardization method was used. The highest quartiles of urinary 2-hydroxynaphthalene (2-NAP) [OR (95% confidence interval (CI)) = 1.46 (1.13, 1.87)] and sum of PAH metabolites [OR (95% CI) = 1.45 (1.13, 1.87)] concentrations were associated with a higher risk of obesity [body mass index (BMI)≥25 kg/m²]. BMI was positively associated with urinary 2-NAP [β (95% CI) = 0.25 (0.09, 0.41), p = 0.003] and sum of PAH metabolites [β (95% CI) = 0.29 (0.08, 0.49), p = 0.006] concentrations. The risk of DM was increased with increasing quartile of 2-hydroxyfluorene (2-OHFlu) and trans, trans-muconic acid (t,t-MA) (p for trend<0.05 and < 0.001, respectively). The highest quartile of t,t-MA showed a significantly higher risk of DM [OR (95% CI) = 2.77 (1.74, 4.42)] and obesity [OR (95% CI) = 1.42 (1.06, 1.90)]. Urinary t,t,-MA level was positively associated with BMI [(β (95% CI) = 0.51 (0.31, 0.71), p < 0.001] and non-alcoholic fatty liver disease index [(β (95% CI) = 0.09 (0.06, 0.12), p < 0.001]. In conclusion, the benzene metabolites t,t-MA and PAH metabolite 2-OHFlu were associated with an increased risk of DM. Urinary biomarkers for PAHs and VOCs were positively associated with BMI in the Korean adult population. Further studies to validate these observations in other populations are warranted.

Clastogenicity and Aneugenicity of 1,4-Benzoquinone in Different Lineages of Mouse Hematopoietic Stem/Progenitor Cells

Previous reports on hematotoxicity and leukemogenicity related to benzene exposure highlighted its adverse effects on hematopoiesis. Despite the reported findings, studies concerning the mechanism of benzene affecting chromosomal integrity in lineage-committed hematopoietic stem/progenitor cells (HSPCs) remain unclear. Here, we studied the clastogenicity and aneugenicity of benzene in lineage-committed HSPCs via karyotyping. Isolated mouse bone marrow cells (MBMCs) were exposed to the benzene metabolite 1,4-benzoquinone (1,4-BQ) at 1.25, 2.5, 5, 7, and 12 μM for 24 h, followed by karyotyping. Then, the chromosomal aberration (CA) in 1,4-BQ-exposed hematopoietic progenitor cells (HPCs) comprising myeloid, Pre-B lymphoid, and erythroid lineages were evaluated following colony-forming cell (CFC) assay. Percentage of CA, predominantly via Robertsonian translocation (Rb), was increased significantly (p < 0.05) in MBMCs and all progenitors at all concentrations. As a comparison, Pre-B lymphoid progenitor demonstrated a significantly higher percentage of CA (p < 0.05) than erythroid progenitor at 1.25, 2.5, and 7 μM as well as a significantly higher percentage (p < 0.05) than myeloid progenitor at 7 μM of 1,4-BQ. In conclusion, 1,4-BQ induced CA, particularly via Rb in both MBMCs and HPCs, notably via a lineage-dependent response. The role of lineage specificity in governing the clastogenicity and aneugenicity of 1,4-BQ deserves further investigation.

Fabrication of an Extremely Cheap Poly(3,4-ethylenedioxythiophene) Modified Pencil Lead Electrode for Effective Hydroquinone Sensing

Hydroquinone (HQ) is one of the major deleterious metabolites of benzene in the human body, which has been implicated to cause various human diseases. In order to fabricate a feasible sensor for the accurate detection of HQ, we attempted to electrochemically modify a piece of common 2B pencil lead (PL) with the conductive poly(3,4-ethylenedioxythiophene) or PEDOT film to construct a PEDOT/PL electrode. We then examined the performance of PEDOT/PL in the detection of hydroquinone with different voltammetry methods. Our results have demonstrated that PEDOT film was able to dramatically enhance the electrochemical response of pencil lead electrode to hydroquinone and exhibited a good linear correlation between anodic peak current and the concentration of hydroquinone by either cyclic voltammetry or linear sweep voltammetry. The influences of PEDOT film thickness, sample pH, voltammetry scan rate, and possible chemical interferences on the measurement of hydroquinone have been discussed. The PEDOT film was further characterized by SEM with EDS and FTIR spectrum, as well as for stability with multiple measurements. Our results have demonstrated that the PEDOT modified PL electrode could be an attractive option to easily fabricate an economical sensor and provide an accurate and stable approach to monitoring various chemicals and biomolecules.

Filling the gap between risk assessment and molecular determinants of tumor onset

In the past two decades, a ponderous epidemiological literature has causally linked tumor onset to environmental exposure to carcinogens. As consequence, risk assessment studies have been carried out with the aim to identify both predictive models of estimating cancer risks within exposed populations and establishing rules for minimizing hazard when handling carcinogenic compounds. The central assumption of these works is that neoplastic transformation is directly related to the mutational burden of the cell without providing further mechanistic clues to explain increased cancer onset after carcinogen exposure. Nevertheless, in the last few years, a growing number of studies have implemented the traditional models of cancer etiology, proposing that neoplastic transformation is a complex process in which several parameters and crosstalk between tumor and microenvironmental cells must be taken into account and integrated with mutagenesis. In this conceptual framework, the current strategies of risk assessment that are solely based on the 'mutator model' require an urgent update and revision to keep pace with advances in our understanding of cancer biology. We will approach this topic revising the most recent theories on the biological mechanisms involved in tumor formation in order to envision a roadmap leading to a future regulatory framework for a new, protective policy of risk assessment.

Bone Marrow Oxidative Stress and Acquired Lineage-Specific Genotoxicity in Hematopoietic Stem/Progenitor Cells Exposed to 1,4-Benzoquinone

Hematopoietic stem/progenitor cells (HSPCs) are susceptible to benzene-induced genotoxicity. However, little is known about the mechanism of DNA damage response affecting lineage-committed progenitors for myeloid, erythroid, and lymphoid. Here, we investigated the genotoxicity of a benzene metabolite, 1,4-benzoquinone (1,4-BQ), in HSPCs using oxidative stress and lineage-directed approaches. Mouse bone marrow cells (BMCs) were exposed to 1,4-BQ (1.25–12 μM) for 24 h, followed by oxidative stress and genotoxicity assessments. Then, the genotoxicity of 1,4-BQ in lineage-committed progenitors was evaluated using colony forming cell assay following 7–14 days of culture. 1,4-BQ exposure causes significant decreases (p < 0.05) in glutathione level and superoxide dismutase activity, along with significant increases (p < 0.05) in levels of malondialdehyde and protein carbonyls. 1,4-BQ exposure induces DNA damage in BMCs by significantly (p < 0.05) increased percentages of DNA in tail at 7 and 12 μM and tail moment at 12 μM. We found crucial differences in genotoxic susceptibility based on percentages of DNA in tail between lineage-committed progenitors. Myeloid and pre-B lymphoid progenitors appeared to acquire significant DNA damage as compared with the control starting from a low concentration of 1,4-BQ exposure (2.5 µM). In contrast, the erythroid progenitor showed significant damage as compared with the control starting at 5 µM 1,4-BQ. Meanwhile, a significant (p < 0.05) increase in tail moment was only notable at 7 µM and 12 µM 1,4-BQ exposure for all progenitors. Benzene could mediate hematological disorders by promoting bone marrow oxidative stress and lineage-specific genotoxicity targeting HSPCs.

Benzene Exposure Induces Insulin Resistance in Mice

Benzene is a ubiquitous pollutant associated with hematotoxicity but its metabolic effects are unknown. We sought to determine if and how exposure to volatile benzene impacted glucose handling. We exposed wild type C57BL/6 mice to volatile benzene (50 ppm × 6 h/day) or HEPA-filtered air for 2 or 6 weeks and measured indices of oxidative stress, inflammation, and insulin signaling. Compared with air controls, we found that mice inhaling benzene demonstrated increased plasma glucose (p = .05), insulin (p = .03), and HOMA-IR (p = .05), establishing a state of insulin and glucose intolerance. Moreover, insulin-stimulated Akt phosphorylation was diminished in the liver (p = .001) and skeletal muscle (p = .001) of benzene-exposed mice, accompanied by increases in oxidative stress and Nf-κb phosphorylation (p = .025). Benzene-exposed mice also demonstrated elevated levels of Mip1-α transcripts and Socs1 (p = .001), but lower levels of Irs-2 tyrosine phosphorylation (p = .0001). Treatment with the superoxide dismutase mimetic, TEMPOL, reversed benzene-induced effects on oxidative stress, Nf-κb phosphorylation, Socs1 expression, Irs-2 tyrosine phosphorylation, and systemic glucose intolerance. These findings suggest that exposure to benzene induces insulin resistance and that this may be a sensitive indicator of inhaled benzene toxicity. Persistent ambient benzene exposure may be a heretofore unrecognized contributor to the global human epidemics of diabetes and cardiovascular disease.

Meta-Analysis Reveals the Association Between Male Occupational Exposure to Solvents and Impairment of Semen Parameters

OBJECTIVES

Solvent exposure is among the most common occupational exposures to chemical toxicants; data about the impact of such exposure on semen parameters are contradictory. We conducted the first meta-analysis to evaluate the risk of alteration in semen parameters related to occupational exposure to solvents.

METHODS

From the PubMed database, we selected studies analyzing the semen of subjects occupationally exposed to solvents, compared with unexposed controls. The meta-analysis was performed on the various semen parameters analyzed in both populations.

RESULTS

Seven studies were included in the study. The meta-analysis revealed a significant decrease in ejaculate volume [standardized mean difference (SMD) = -0.35 (-0.63 to -0.07)] and sperm concentration [SMD = -0.36 (-0.64 to -0.08)] in workers exposed to solvents compared with unexposed controls.

CONCLUSION

Our results highlight the importance of preventing reprotoxic risks to male fertility in the workplace.

Overexpression of HIF-1a could partially protect K562 cells from 1,4-benzoquinone induced toxicity by inhibiting ROS, apoptosis and enhancing glycolysis

Benzene is an environmental contaminant which causes hematological diseases. Previously, hypoxia inducible factor-1a (HIF-1a) was found to be involved in benzene-induced hematotoxicity. This study aims to explore whether overexpression of HIF-1a in K562 cell line could influence the toxicity caused by 1,4-BQ. HIF-1a overexpression K562 cell line was constructed with a lentiviral vector. Results showed that HIF-1a was significantly elevated in control K562 cells and HIF-1a overexpression cells exposed to 1,4-BQ. Compared with 1,4-BQ exposed control cells, HIF-1a overexpression blocked cell cycle at G2/M phase, remarkably reduced apoptosis and ROS level. And HIF-1a overexpression caused downregulation of Nox4 and upregulation of Bcl-2. In addition, the lactic acid (LD)/pyruvic acid (PA) ratio was significantly higher in HIF-1a overexpression cells than that in control cells at the same 1,4-BQ dose. Furthermore, significant increases in Glut1, Ldha, Pkm2, Pgk1, Pdk1, Pfkl, Pfkfb3 protein levels was also observed in HIF-1a overexpression cells. Overall, our results indicated that HIF-1a overexpression could alleviate ROS and apoptosis caused by 1,4-BQ through targeting Nox4, Bcl-2 and key enzymes in glycolysis.

Epigenetic and Transcriptional Modifications in Repetitive Elements in Petrol Station Workers Exposed to Benzene and MTBE

Benzene, a known human carcinogen, and methyl tert-butyl ether (MTBE), not classifiable as to its carcinogenicity, are fuel-related pollutants. This study investigated the effect of these chemicals on epigenetic and transcriptional alterations in DNA repetitive elements. In 89 petrol station workers and 90 non-occupationally exposed subjects the transcriptional activity of retrotransposons (LINE-1, Alu), the methylation on repeated-element DNA, and of H3K9 histone, were investigated in peripheral blood lymphocytes. Median work shift exposure to benzene and MTBE was 59 and 408 µg/m³ in petrol station workers, and 4 and 3.5 µg/m³, in controls. Urinary benzene (BEN-U), S-phenylmercapturic acid, and MTBE were significantly higher in workers than in controls, while trans,trans-muconic acid (tt-MA) was comparable between the two groups. Increased BEN-U was associated with increased Alu-Y and Alu-J expression; moreover, increased tt-MA was associated with increased Alu-Y and Alu-J and LINE-1 (L1)-5'UTR expression. Among repetitive element methylation, only L1-Pa5 was hypomethylated in petrol station workers compared to controls. While L1-Ta and Alu-YD6 methylation was not associated with benzene exposure, a negative association with urinary MTBE was observed. The methylation status of histone H3K9 was not associated with either benzene or MTBE exposure. Overall, these findings only partially support previous observations linking benzene exposure with global DNA hypomethylation.

Benzoquinone induces ROS-dependent mitochondria-mediated apoptosis in HL-60 cells

Benzene exposure affects the hematopoietic system and leads to the occurrence of various types of leukemia and hematotoxicity. It has been confirmed that active metabolites of benzene, including 1,4-benzoquinone (1,4-BQ), can induce reactive oxygen species (ROS) and apoptosis in the bone marrow, and recent studies have also suggested that benzene exposure can affect mitochondrial function in both experimental animals and cell lines. However, the potential relationship among ROS production, mitochondrial damages, and subsequent apoptosis following benzene exposure has not been well studied in detail. In the present study, we utilized HL-60 cells, a well-characterized human myeloid cell line, as an in vitro model and examined the effects of 1,4-BQ on intracellular ROS formation, mitochondria damage, and the occurrence of apoptotic events with or without using the ROS scavenger N-acetyl-l-cysteine (NAC). The results demonstrated that 1,4-BQ could dose-dependently induce production of ROS and mitochondrial damage as characterized by mitochondrial membrane potential disruption, mitochondrial ultrastructure alteration, and induced apoptosis and activated caspase-3 and caspase-9. Preincubation of HL-60 cells with NAC prior to 1,4-BQ treatment could block 1,4-BQ-induced production of ROS and the occurrence of apoptosis. These results demonstrated that 1,4-BQ induced apoptosis in HL-60 cells through a ROS-dependent mitochondrial-mediated pathway.

Application of cell-based assays for toxicity characterization of complex wastewater matrices: Possible applications in wastewater recycle and reuse

Exposure to pre-concentrated inlet or outlet STP wastewater extracts at different concentrations (0.001% to 1%) induced dose-dependent toxicity in MCF-7 cells, whereas drinking water extracts did not induce cytotoxicity in cells treated. GC-MS analysis revealed the occurrence of xenobiotic compounds (Benzene, Phthalate, etc.) in inlet/outlet wastewater extracts. Cells exposed to inlet/outlet extract showed elevated levels of reactive oxygen species (ROS: inlet: 186.58%, p<0.05, outlet, 147.8%, p<0.01) and loss of mitochondrial membrane potential (Δψm: inlet, 74.91%, p<0.01; outlet, 86.70%, p<0.05) compared to the control. These concentrations induced DNA damage (Tail length: inlet: 34.4%, p<0.05, outlet, 26.7%, p<0.05) in treated cells compared to the control (Tail length: 7.5%). Cell cycle analysis displayed drastic reduction in the G1 phase in treated cells (inlet, G1:45.0%; outlet, G1:58.3%) compared to the control (G1:67.3%). Treated cells showed 45.18% and 28.0% apoptosis compared to the control (1.2%). Drinking water extracts did not show any significant alterations with respect to ROS, Δψm, DNA damage, cell cycle and apoptosis compared to the control. Genes involved in cell cycle and apoptosis were found to be differentially expressed in cells exposed to inlet/outlet extracts. Herein, we propose cell-based toxicity assays to evaluate the efficacies of wastewater treatment and recycling processes.

Elevated monocyte phosphorylated p38 in nearby employees after a chemical explosion

Personalised health surveillance is infrequent or absent in occupational and environmental medicine. The shortage of functional tests in relevant cells and tissues greatly limits our understanding of environmental exposures and associated disease risk. We evaluated single cell signalling in peripheral blood mononuclear cells from 301 individuals in a cross sectional health survey 18 months after a chemical explosion of sulphorous coker gasoline. The accident created a malodourous environment leading to long-term health complaints. Multiple regression analysis revealed T-cell specific elevated phosphorylation of the stress kinase p-p38 (T180/Y182) among tobacco smokers and monocyte-specific elevated phosphorylation in employees at the explosion site. Other studies of the accident reported reduced tear film stability, and more airway obstruction and subjective health complaints among the employees at the accident site. Elevated monocyte p-p38 in the employee group was independent of such health effects, and could therefore be dependent on the sulphuric malodorous environment. The present study proposes signalling status in leukocytes as a scalable biomarker providing information about environmental exposures.

Combined chemoassay and mass spectrometric approach to study the reactive potential of electrophiles towards deoxynucleosides as model for DNA

The modification of DNA by adduct formation is a potential molecular initiating event of genotoxicity. A chemoassay was established to study adduct formation of electrophiles with deoxynucleosides. Liquid chromatography-mass spectrometry was used to determine the reactivity of the model electrophiles para-benzoquinone, hydroquinone, and 1,4-naphthoquinone with deoxynucleoside (deoxyadenosine (dA), deoxyguanosine (dG), deoxycytidine (dC) and thymidine (dT)) to detect formation of adducts via constant neutral loss scan of deoxyribose (116 Da), and to elucidate adduct structures using high resolution mass spectrometry. Of the four deoxynucleosides dG was most susceptible, followed by dC and para-benzoquinone was the most reactive electrophile. With this approach five dG and four dC adducts were detected, formed by Michael addition and subsequent condensation. Also oxidation occurred with reactive oxygen species (ROS). Three of the adducts formed by benzoquinone have not been reported before. This chemoassay combined with mass spectrometry offers a way (a) to screen a large number of chemicals for their genotoxic potential, (b) to determine novel adducts that may be searched for in in vitro and in vivo studies and thus (c) to better understand the reaction of electrophiles with nucleobases.

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.

Phenolic metabolites of benzene induced caspase-dependent cytotoxicities to K562 cells accompanied with decrease in cell surface sialic acids

Benzene-induced erythropoietic depression has been proposed to be due to the production of toxic metabolites. Presently, the cytotoxicities of benzene metabolites, including phenol, catechol, hydroquinone, and 1,2,4-benzenetriol, to erythroid progenitor-like K562 cells were investigated. After exposure to these metabolites, K562 cells showed significant inhibition of viability and apoptotic characteristics. Each metabolite caused a significant increase in activities of caspase-3, -8, and -9, and pretreatment with caspase-3, -8, and -9 inhibitors significantly inhibited benzene metabolites-induced phosphatidylserine exposure. These metabolites also elevated expression of Fas and FasL on the cell surface. After exposure to benzene metabolites, K562 cells showed an increase in reactive oxygen species level, and pretreatment with N-acetyl-l-cysteine significantly protected against the cytotoxicity of each metabolite. Interestingly, the control K562 cells and the phenol-exposed cells aggregated together, but the cells exposed to other metabolites were scattered. Further analysis showed that hydroquione, catechol, and 1,2,4-benzenetriol induced a decrease in the cell surface sialic acid levels and an increase in the cell surface sialidase activity, but phenol did not cause any changes in sialic acid levels and sialidase activity. Consistently, an increase in expression level of sialidase Neu3 mRNA and a decrease in mRNA level of sialyltransferase ST3GAL3 gene were detected in hydroquione-, catechol-, or 1,2,4-benzenetriol-treated cells, but no change in mRNA levels of two genes were found in phenol-treated cells. In conclusion, these benzene metabolites could induce apoptosis of K562 cells mainly through caspase-8-dependent pathway and ROS production, and sialic acid metabolism might play a role in the apoptotic process.

Current understandings and perspectives on non-cancer health effects of benzene: a global concern

OBJECTIVE

Benzene, as a volatile organic compound, is known as one of the main air pollutants in the environment. The aim of this review is to summarize all available evidences on non-cancerous health effects of benzene providing an overview of possible association of exposure to benzene with human chronic diseases, specially, in those regions of the world where benzene concentration is being poorly monitored.

METHODOLOGY

A bibliographic search of scientific databases including PubMed, Google Scholar, and Scirus was conducted with key words of "benzene toxic health effects", "environmental volatile organic compounds", "diabetes mellitus and environmental pollutants", "breast cancer and environmental pollution", "prevalence of lung cancer", and "diabetes prevalence". More than 300 peer reviewed papers were examined. Experimental and epidemiologic studies reporting health effects of benzene and volatile organic compounds were included in the study.

RESULTS

Epidemiologic and experimental studies suggest that benzene exposure can lead to numerous non-cancerous health effects associated with functional aberration of vital systems in the body like reproductive, immune, nervous, endocrine, cardiovascular, and respiratory.

CONCLUSION

Chronic diseases have become a health burden of global dimension with special emphasis in regions with poor monitoring over contents of benzene in petrochemicals. Benzene is a well known carcinogen of blood and its components, but the concern of benzene exposure is more than carcinogenicity of blood components and should be evaluated in both epidemiologic and experimental studies. Aspect of interactions and mechanism of toxicity in relation to human general health problems especially endocrine disturbances with particular reference to diabetes, breast and lung cancers should be followed up.

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.

Metabonomics biomarkers for subacute toxicity screening for benzene exposure in mice

Benzene is known to produce hematotoxicity in occupational exposure workers. This study examined the utility of metabonomic biomarkers to ascertain subacute toxicity produced by benzene in male C3H/He mice. A 30-d intermittent collection of urine was obtained from mice in this experiment. The relative organ weights, blood parameters, and bone marrow smears were examined to identify specific changes of benzene-induced toxicity. In addition, an integrated analytical approach based on liquid chromatography coupled with mass spectrometry (LC-MS) was developed to map metabolic responses in urine. Five endogenous metabolites, hypoxanthine, spermidine, 4-aminohippuric acid, indolelactic acid, and glutamylphenylalanine, were identified as potential biomarkers of benzene-induced toxicity, indicating that pathways of purine, spermidine, fatty acid, tryptophan, and peptides metabolism might be disturbed in benzene-exposed mice. Our findings showed that the use of urine metabonomics was a more sensitive tool to detect benzene-induced toxicity compared to body weight or blood parameter changes.

Mitochondria and reactive oxygen species. Which role in physiology and pathology?

Oxidative stress is among the major causes of toxicity due to interaction of Reactive Oxygen Species (ROS) with cellular macromolecules and structures and interference with signal transduction pathways. The mitochondrial respiratory chain, specially from Complexes I and III, is considered the main origin of ROS particularly under conditions of high membrane potential, but several other sources may be important for ROS generation, such as mitochondrial p66(Shc), monoamine oxidase, α-ketoglutarate dehydogenase, besides redox cycling of redox-active molecules. ROS are able to oxidatively modify lipids, proteins, carbohydrates and nucleic acids in mitochondria and to activate/inactivate signalling pathways by oxidative modification of redox-active factors. Cells are endowed with several defence mechanisms including repair or removal of damaged molecules, and antioxidant systems, either enzymatic or non-enzymatic. Oxidative stress is at the basis of ageing and many pathological disorders, such as ischemic diseases, neurodegenerative diseases, diabetes, and cancer, although the underlying mechanisms are not always completely understood.

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.

Identification of senescence-inducing microRNAs in normal human keratinocytes

MicroRNAs (miRNAs) are epigenetic regulators of eukaryotic gene expression and play key roles in many cellular processes. However, the role of miRNAs for replicative senescence of normal human keratinocytes (NHKs) remains unknown. Thus, we examined the expression profiles of 847 miRNAs in exponentially replicating and senescent NHKs and identified 126 senescence-associated miRNAs (SA-miRs). Among SA-miRs, 117 miRNAs (93%) were upregulated and 9 miRNAs (7%) were downregulated in senescent NHKs compared to those of exponentially replicating cells. Among the above miRNAs, we selected two miRNAs, miR-137 and miR-668, for further investigation because they were consistently upregulated with replicative senescence of three independent NHK cultures. Ectopic overexpression of miR-137 or miR-668 induced senescence in rapidly proliferating NHKs; a notable increase in senescence-associated β-galactosidase activity, p16INK4A and p53 was observed, indicating that they are novel senescence-inducing miRNAs. In addition, these senescence-inducing miRNAs were gradually increased during organismal aging of normal human oral epithelia. We also detected downregulation of miR-137 and miR-668 in many tested human head and neck squamous cell carcinoma cell lines. Since senescence would be viewed as a potent tumor suppressive pathway, the newly identified senescence-inducing miRNAs deserve to be further investigated for their therapeutic application in cancer treatment.

Cytotoxic and genotoxic effects of defence secretion of Ulomoides dermestoides on A549 cells

ETHNOPHARMACOLOGICAL RELEVANCE

Ulomoides dermestoides (Fairmaire, 1893) is a cosmopolitan tenebrionid beetle reared by Argentine people who consume them alive as an alternative medicine in the treatment of different illnesses such as asthma, Parkinson's, diabetes, arthritis, HIV and specially cancer.

AIM OF THE STUDY

To evaluate the cytotoxicity and DNA damage of the major volatile components released by Ulomoides dermestoides on human lung carcinoma epithelial cell line A549.

MATERIALS AND METHODS

The defence compounds of Ulomoides dermestoides were extracted with dichloromethane and analyzed and quantified by capillary gas chromatography. The toxicity effects of the beetle's extract against A549 cell line were evaluated. Cytotoxicity was evaluated by MTT test and Trypan blue assay and genotoxicity was evaluated by the comet assay. The synthetic compounds, individually or combined, were also tested in A549 cells and normal mononuclear human cells.

RESULTS

The defence compounds of Ulomoides dermestoides extracted with dichloromethane (methyl-1,4-benzoquinones, ethyl-1,4-benzoquinones and 1-pentadecene as major components) showed cytotoxic activity on A549 cells demonstrated by MTT test and Trypan blue assay, with IC(50) values of 0.26equivalent/ml and 0.34equivalent/ml, respectively (1equivalent=amount of components extracted per beetle). The inhibition of A549 cell proliferation with the synthetic blend (1,4-benzoquinone and 1-pentadecene) or 1,4-benzoquinone alone was similar to that obtained with the insect extract. 1-Pentadecene showed no inhibitory effect. Low doses of insect extract or synthetic blend (0.15equivalent/ml) inhibited mononuclear cell proliferation by 72.2±2.7% and induced significant DNA damage both in tumor and mononuclear cells.

CONCLUSION

Results of this study demonstrated that defence compounds of Ulomoides dermestoides reduced cell viability and induced DNA damage. We also concluded that the insect benzoquinones are primarily responsible for inducing cytotoxicity and genotoxicity in culture cells.

Modulation of phase-II enzyme activities in benzene treated ovariectomized rats

The aim of the study was to determine the influence of ovariectomy on phase II enzymes viz. glutathione-S-transferase (GST), glutathione peroxidase (GPX) and catalase (CAT) in liver and kidney of female rats treated with benzene. The results showed the significant decrease of the GST and GPX activity in benzene treated rats after ovariectomy. However progesterone supplementation stimulated the activity of GST and GPX in liver and kidney of benzene treated non ovariectomized and ovariectomized rats. Progesterone supplementation to benzene treated ovariectomized rats helps to gain in CAT activity. Our results on DNA damage using single cell gel electrophoresis also confirmed our findings on antioxidant enzymes. The results showed that lack of protective progesterone against benzene toxicity is reflected in alterations in antioxidant enzyme activities. However progesterone therapy to benzene treated ovariectomized rats results in activating the antioxidant defence system. Since female workers are engaged in industrial sector, these results are important from occupational health point of view. Benzene exposure affects their reproductive health. Nevertheless, it could be modulated by suitable hormonal therapy.

Structure and organization of mitochondrial respiratory complexes: a new understanding of an old subject

The enzymatic complexes of the mitochondrial respiratory chain have been extensively investigated in their structural and functional properties. A clear distinction is possible today between three complexes in which the difference in redox potential allows proton translocation (complexes I, III, and IV) and those having the mere function to convey electrons to the respiratory chain. We also have a clearer understanding of the structure and function of most respiratory complexes, of their biogenesis and regulation, and of their capacity to generate reactive oxygen species. Past investigations led to the conclusion that the complexes are randomly dispersed and functionally connected by diffusion of smaller redox components, coenzyme Q and cytochrome c. More-recent investigations by native gel electrophoresis and single-particle image processing showed the existence of supramolecular associations. Flux-control analysis demonstrated that complexes I and III in mammals and I, III, and IV in plants kinetically behave as single units, suggesting the existence of substrate channeling. This review discusses conditions affecting the formation of supercomplexes that, besides kinetic advantage, have a role in the stability and assembly of the individual complexes and in preventing excess oxygen radical formation. Disruption of supercomplex organization may lead to functional derangements responsible for pathologic changes.

The role of catechols and free radicals in benzene toxicity: an oxidative DNA damage pathway

Benzene is a widespread volatile compound and an environmental contaminant. Since it causes important toxic effects in workers exposed to low levels, long-term exposure to this compound has been extensively studied. Leukemia, blood disorders, bone marrow depression, and some types of cancer are directly related to benzene-initiated toxicity. Bioactivation of benzene can lead to the formation of hazardous metabolites such as phenol, hydroquinone, and catechol. Catechol forms semiquinones and reactive quinones that are presumed to play an important role in the generation of reactive oxygen species (ROS). ROS formation can directly induce single and double strand breaks in the DNA, oxidized nucleotides, and hyper-recombination, and consequently produces deleterious genetic changes. In this review, we have addressed the cytotoxic effects of benzene and its main metabolite, catechol, focusing on the oxidative pathway and further DNA damage.

Risk assessment of hydroquinone: differential responses of cell growth and lethality correlated to hydroquinone concentration

Hydroquinone (HQ) is a major metabolite of benzene and has been used as an antioxidant, a stabilizer, a photographic reducer, and an ingredient in skin lighteners. In this study, the effects of low (5 microM) and high (50 microM) concentrations of HQ were investigated on cell growth and lethality in Jurkat cells. Intracellular reactive oxygen species (ROS) levels were increased with both HQ concentrations. Fifty micromolar HQ markedly increased phosphorylation of ERK and activation of caspase-9/-3, followed by PARP cleavage. The addition of ERK inhibitor PD98059 or N-acetylcysteine (NAC) abolished HQ-induced apoptosis. Five micromolar HQ activated ERK protein, but not JNK or p38. However, S-phase recruitment was decreased by preincubation with NAC, but not PD98059. Thus, high levels of ROS contributed to HQ-induced apoptosis via ERK signaling and the caspase pathway, whereas low quantities of ROS resulted in S-phase recruitment in the cell-cycle distribution.

The DNA cleavage reaction of topoisomerase II: wolf in sheep's clothing

Topoisomerase II is an essential enzyme that is required for virtually every process that requires movement of DNA within the nucleus or the opening of the double helix. This enzyme helps to regulate DNA under- and overwinding and removes knots and tangles from the genetic material. In order to carry out its critical physiological functions, topoisomerase II generates transient double-stranded breaks in DNA. Consequently, while necessary for cell survival, the enzyme also has the capacity to fragment the genome. The DNA cleavage/ligation reaction of topoisomerase II is the target for some of the most successful anticancer drugs currently in clinical use. However, this same reaction also is believed to trigger chromosomal translocations that are associated with specific types of leukemia. This article will familiarize the reader with the DNA cleavage/ligation reaction of topoisomerase II and other aspects of its catalytic cycle. In addition, it will discuss the interaction of the enzyme with anticancer drugs and the mechanisms by which these agents increase levels of topoisomerase II-generated DNA strand breaks. Finally, it will describe dietary and environmental agents that enhance DNA cleavage mediated by the enzyme.

Reactive species: a cell damaging rout assisting to chemical carcinogens

Reactive oxygen and nitrogen species (ROS and RNS) are known to contribute as pathogenic factors to the development of chronic progressive diseases at various stages. The present review discusses the role of oxidative stress in chemically induced cancer development and progression. Reactive species are capable of inducing DNA damage that eventually may contribute to cell transformation and tumor initiation. ROS and RNS are also associated with tumor promotion and progression. Both endogenous processes and redox-cycling of xenobiotic compounds have been shown to result in oxidative DNA damage. In addition, several exocyclic DNA adducts represent secondary DNA damage caused by products of lipid peroxidation in the course of oxidative cellular stress. Due to their intrinsic ability to catalyze redox reactions, transition metals, and quinones from various classes of xenobiotics or endogenous compounds are important mediators of oxidative stress and thus likely of being involved in DNA damage, lipid peroxidation, cell transformation, and tumor development.

A review of the role of benzene metabolites and mechanisms in malignant transformation: summative evidence for a lack of research in nonmyelogenous cancer types

The aromatic hydrocarbon benzene is a well-recognised haematotoxin and carcinogen associated with malignancy in occupational environments. Primary benzene metabolites phenol, catechol, and hydroquinone are implicated in the progression from cytotoxicity to carcinogenicity, and malignant transformation in myelogenous cell lineage is hypothesised to encompass a complex multistep process involving gene mutations in cell signalling and mitosis, oncogene activation, downregulated immune-mediated tumour surveillance, anti-apoptotic activities, and genetic susceptibility. Several mechanisms of carcinogenicity are proposed but none are accepted widely as causative. Involvement of covariables such as duration and frequency of benzene exposure, metabolite concentration, and degree of biological interactions provides a theoretical framework for a multiple mechanistic model to explain cytotoxic-malignant transformation. Despite significant research in myeloid leukaemias, limited biological and epidemiological studies on benzene and its metabolites in nonhaematopoietic malignancies suggests more research is needed to determine its role in contributing to other cancer types.

Association of the NQO1, MPO, and XRCC1 polymorphisms and chromosome damage among workers at a petroleum refinery

Benzene is a leukemogen, and exposure to benzene is an occupational hazard in the petroleum refining industries. The effects of genetic polymorphisms in the NQO1 (rs1800566), MPO (rs2333227), and XRCC1 (rs25487) genes on benzene-induced chromosome abnormalities were assessed in 108 benzene-exposed workers and 33 office workers. The mean benzene exposure for exposed workers was 0.51 ppm for full-shift workers, and the time-weighted average ranged from 0.004 to 4.25 ppm. The frequencies of micronuclei (MN) and chromosome aberrations (CA) were significantly higher in workers exposed to benzene than unexposed controls. Exposed workers with the T/T genotype for NQO1 showed significant 1.9-fold (95% CI = 1.5-2.3) and 2.6-fold (95% CI = 1.7-3.9) increases in MN and CA frequencies, respectively, compared to controls with C/C and C/T genotypes, after adjusting for age, smoking status, and alcohol intake. Among exposed workers, subjects with the combination of MPO G/G and XRCC1 Arg/Gln or Gln/Gln showed a significantly higher CA frequency compared to those with the combination of MPO G/A or A/A and XRCC1 Arg/Arg genotypes. These results indicated that the genotoxicity induced by a chronic benzene exposure is modulated by genes involved in both DNA repair and benzene metabolic pathways.

Proteomic Analysis Identifies Oxidative Stress Induction by Adaphostin

PURPOSE

Activities distinct from inhibition of Bcr/abl have led to adaphostin (NSC 680410) being described as "a drug in search of a mechanism." In this study, proteomic analysis of adaphostin-treated myeloid leukemia cell lines was used to further elucidate a mechanism of action.

EXPERIMENTAL DESIGN

HL60 and K562 cells treated with adaphostin for 6, 12, or 24 h were analyzed using two-dimensional PAGE. Differentially expressed spots were excised, digested with trypsin, and analyzed by liquid chromatography-tandem mass spectrometry. The contribution of the redox-active hydroquinone group in adaphostin was also examined by carrying out proteomic analysis of HL60 cells treated with a simple hydroquinone (1,4-dihydroxybenzene) or H(2)O(2).

RESULTS

Analysis of adaphostin-treated cells identified 49 differentially expressed proteins, the majority being implicated in the response to oxidative stress (e.g., CALM, ERP29, GSTP1, PDIA1) or induction of apoptosis (e.g., LAMA, FLNA, TPR, GDIS). Interestingly, modulation of these proteins was almost fully prevented by inclusion of an antioxidant, N-acetylcysteine. Validation of the proteomic data confirmed GSTP1 as an adaphostin resistance gene. Subsequent analysis of HL60 cells treated with 1,4-dihydroxybenzene or H(2)O(2) showed similar increases in intracellular peroxides and an almost identical proteomic profiles to that of adaphostin treatment. Western blotting of a panel of cell lines identified Cu/Zn superoxide dismutase (SOD) as correlating with adaphostin resistance. The role of SOD as a second adaphostin resistance gene was confirmed by demonstrating that inhibition of SOD using diethyldithiocarbamate increased adaphostin sensitivity, whereas transfection of SOD I attenuated toxicity. Importantly, treatment with 1,4-dihydroxybenzene or H(2)O(2) replicated adaphostin-induced Bcr/abl polypeptide degradation, suggesting that kinase inhibition is a ROS-dependent phenomenon.

CONCLUSION

Adaphostin should be classified as a redox-active-substituted dihydroquinone.

Valproic Acid Increases Conservative Homologous Recombination Frequency and Reactive Oxygen Species Formation: A Potential Mechanism for Valproic Acid-Induced Neural Tube Defects

Valproic acid, a commonly used antiepileptic agent, is associated with a 1 to 2% incidence of neural tube defects when taken during pregnancy; however, the molecular mechanism by which this occurs has not been elucidated. Previous research suggests that valproic acid exposure leads to an increase in reactive oxygen species (ROS). DNA damage due to ROS can result in DNA double-strand breaks, which can be repaired through homologous recombination (HR), a process that is not error-free and can result in detrimental genetic changes. Because the developing embryo requires tight regulation of gene expression to develop properly, we propose that the loss or dysfunction of genes involved in embryonic development through aberrant HR may ultimately cause neural tube defects. To determine whether valproic acid induces HR, Chinese hamster ovary 3-6 cells, containing a neomycin direct repeat recombination substrate, were exposed to valproic acid for 4 or 24 h. A significant increase in HR after exposure to valproic acid (5 and 10 mM) for 24 h was observed, which seems to occur through a conservative HR mechanism. We also demonstrated that exposure to valproic acid (5 and 10 mM) significantly increased intracellular ROS levels, which were attenuated by preincubation with polyethylene glycol-conjugated (PEG)-catalase. A significant change in the ratio of 8-hydroxy-2'-deoxyguanosine/2'-de-oxyguanosine, a measure of DNA oxidation, was not observed after valproic acid exposure; however, preincubation with PEG-catalase significantly blocked the increase in HR. These data demonstrate that valproic acid increases HR frequency and provides a possible mechanism for valproic acid-induced neural tube defects.

Protective effect of 1,2,4-benzenetriol on LPS-induced NO production by BV2 microglial cells

Hydroxyhydroquinone or 1,2,4-benzenetriol (BT) detected in the beverages has a structure that coincides with the water-soluble form of a sesame lignan, sesamol. We previously showed that sesame antioxidants had neuroprotective abilities due to their antioxidant properties and/or inducible nitric oxide synthase (iNOS) inhibition. However, studies show that BT can induce DNA damage through the generation of reactive oxygen species (ROS). Therefore, we were interested to investigate the neuroprotective effect of BT in vitro and in vivo. The results showed that instead of enhancing free radical generation, BT dose-dependently (10-100 microM) attenuated nitrite production, iNOS mRNA and protein expression in lipopolysaccharide (LPS)-stimulated murine BV-2 microglia. BT significantly reduced LPS-induced NF-kappaB and p38 MAPK activation. It also significantly reduced the generation of ROS in H2O2-induced BV-2 cells and in H2O2-cellfree conditions. The neuroprotective effect of BT was further demonstrated in the focal cerebral ischemia model of Sprague-Dawley rat. Taken together, the inhibition of LPS-induced nitrite production might be due to the suppression of NF-kappaB, p38 MAPK signal pathway and the ROS scavenging effect. These effects might help to protect neurons from the ischemic injury.

Benzene increases protein-bound 3-nitrotyrosine in bone marrow of B6C3F1 mice

Benzene, an environmental pollutant, is myelotoxic and leukemogenic in humans. The molecular mechanisms that can account for its biological effects have not been fully elucidated. We hypothesize that one of the underlying mechanism involves nitration of proteins by peroxynitrite and/or by bone marrow myeloperoxidase-dependent pathways in nitric oxide (NO) metabolism. Using 3-nitrotyrosine [Tyr(NO(2))] as a biomarker for NO-induced damage to proteins, we examined the effects of benzene on the levels of Tyr(NO(2)) in bone marrow in vivo. Groups of 8 weeks old B6C3F(1) male mice were given a single i.p. injection of benzene (50, 100, 200 or 400mg/kg bodyweight) in corn oil. The mice in control groups received either no treatment or a single injection of the vehicle. The mice were killed 1h after treatment and proteins were isolated from bone marrow, lung, liver and plasma. The proteins were enzymatically hydrolyzed; amino acids were separated and purified by high pressure liquid chromatography, derivatized, and quantified by electron capture-negative chemical ionization-gas chromatography/mass spectrometry (EC-NCI-GC/MS). In the GC/MS assay, 3-nitro-l-[(13)C(9)]tyrosine was used as an internal standard and l-[(2)H(4)]tyrosine served to monitor artifactual formation of 3-nitrotyrosine during sample preparation and analysis. We found that treatment of mice with benzene elevates nitration of tyrosine residues in bone marrow proteins. There was a dose (50-200mg benzene/kg b.w.)-dependent increase in protein-bound Tyr(NO(2)) formation (1.5- to 4.5-fold); however, the levels of Tyr(NO(2)) at 400mg benzene/kg b.w. were significantly higher than control but lower than that formed at 200mg benzene/kg b.w. The results of this study, for the first time, indicate that benzene increases protein-bound 3-Tyr(NO(2)) in bone marrow in vivo, and support our previous finding that benzene is metabolized to nitrated products in bone marrow of mice; collectively, these results may in part account for benzene-induced myelotoxicity.