Urinary S-phenylmercapturic Acid Research Articles

Specific CpG sites methylation is associated with hematotoxicity in low-dose benzene-exposed workers

Benzene is a broadly used industrial chemicals which causes various hematologic abnormalities in human. Altered DNA methylation has been proposed as epigenetic biomarkers in health risk evaluation of benzene exposure, yet the role of methylation at specific CpG sites in predicting hematological effects remains unclear. In this study, we recruited 120 low-level benzene-exposed and 101 control male workers from a petrochemical factory in Maoming City, Guangdong Province, China. Urinary S-phenylmercapturic acid (SPMA) in benzene-exposed workers was 3.40-fold higher than that in control workers (P < 0.001). Benzene-induced hematotoxicity was characterized by reduced white blood cells counts and nuclear division index (NDI), along with an increased DNA damage and urinary 8-hydroxy-2′-deoxyguanosine (all P < 0.05). Methylation levels of TRIM36, MGMT and RASSF1a genes in peripheral blood lymphocytes (PBLCs) were quantified by pyrosequencing. CpG site 6 of TRIM36, CpG site 2, 4, 6 of RASSF1a and CpG site 1, 3 of MGMT methylation were recognized as hot CpG sites due to a strong correlation with both internal exposure and hematological effects. Notably, integrating hot CpG sites methylation of multiple genes reveal a higher efficiency in prediction of integrative damage compared to individual genes at hot CpG sites. The negative dose–response relationship between the combined methylation of hot CpG sites in three genes and integrative damage enabled the classification of benzene-exposed individuals into high-risk or low-risk groups using the median cut-off value of the integrative index. Subsequently, a prediction model for integrative damage in benzene-exposed populations was built based on the methylation status of the identified hot CpG sites in the three genes. Taken together, these findings provide a novel insight into application prospect of specific CpG site methylation as epi-biomarkers for health risk assessment of environmental pollutants.

Leukemia risk assessment of exposure to low-levels of benzene based on the linearized multistage model.

To assess leukemia risk in occupational populations exposed to low levels of benzene. Leukemia incidence data from the Chinese Benzene Cohort Study were fitted using the Linearized multistage (LMS) model. Individual benzene exposure levels, urinary S-phenylmercapturic acid (S-PMA) and trans, trans-muconic acid (t, t-MA) were measured among 98 benzene-exposed workers from factories in China. Subjects were categorized into four groups by rounding the quartiles of cumulative benzene concentrations (< 3, 3-5, 5-12, ≥12 mg/m3·year, respectively). The risk of benzene-induced leukemia was assessed using the LMS model, and the results were validated using the EPA model and the Singapore semi-quantitative risk assessment model. The leukemia risks showed a positive correlation with increasing cumulative concentration in the four exposure groups (excess leukemia risks were 4.34, 4.37, 4.44 and 5.52 × 10-4, respectively; Ptrend < 0.0001) indicated by the LMS model. We also found that the estimated leukemia risk using urinary t, t-MA in the LMS model was more similar to those estimated by airborne benzene compared to S-PMA. The leukemia risk estimated by the LMS model was consistent with both the Singapore semi-quantitative risk assessment model at all concentrations and the EPA model at high concentrations (5-12, ≥12 mg/m3·year), while exceeding the EPA model at low concentrations (< 3 and 3-5 mg/m3·year). However, in all four benzene-exposed groups, the leukemia risks estimated by these three models exceeded the lowest acceptable limit for carcinogenic risk set by the EPA at 1 × 10-6. This study demonstrates the utility of the LMS model derived from the Chinese benzene cohort in assessing leukemia risk associated with low-level benzene exposure, and suggests that leukemia risk may occur at cumulative concentrations below 3 mg/m3·year.

A Hybrid Molecularly Imprinted Polymer for Selective Adsorption of Urinary S-Phenylmercapturic Acid

A hybrid molecular imprinted polymer (HMIP) obtained by the organic monomer 4-vinylpyridine (4-VP) and the inorganic precursor tetraethyl orthosilicate (TEOS) was synthesized for the selective extraction of urinary S-phenylmercapturic acid (u-SPMA), a biomarker of benzene exposure. The chemical and structural characterization of the synthetic adsorbent was performed by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and textural analysis employing N2 adsorption-desorption isotherms. Selective and adsorptive performance of the imprinted polymers were evaluated by kinetic, isothermal, thermodynamic, and selectivity studies. The kinetic data were well adjusted to pseudo-second order and intraparticle diffusion models, leading to selectivity coefficient (K) value of 0.03 g mg-1 min-1 for HMIP. In addition, the adsorption isotherms were better described by the Sip model achieving a maximum adsorption capacity of 284.81 μg g-1 (at 288.15 K).

Early hematopoietic injury triggered by benzene characterized with inhibition of erythrocyte differentiation involving the mollicutes_RF39-derived citrulline.

Benzene poisoning is a common adverse blood outcome in occupational workers, manifested by hematopoietic dysfunction. However, the specific phenotype and its mechanisms of early hematopoietic toxicity caused by benzene remain unclear. After 15 days of exposure, the WBC levels were not significantly altered in benzene-exposed mice. However, the level of red blood cells (RBC) showed a significant decrease, and it was significantly and negatively correlated with urinary S-phenylmercapturic acid (SPMA). Notably, 5mg/kg benzene exposure significantly inhibited the renewal capacity and the number of colony formation of hematopoietic stem progenitor cells in mice, especially erythrocyte differentiation. These results suggested that the early hematopoietic toxicity phenotype caused by benzene was dominated by inhibition of erythroid differentiation rather than WBC-related inflammation. To further understand the underlying mechanisms of benzene-induced early hematopoietic toxicity, 16S rRNA sequencing and plasma metabolites analysis were conducted to investigate the impact of benzene exposure for 15 days on microbial composition and metabolic profile of mice. We found that short-term benzene exposure induced disturbances in gut microbiota and metabolism. The relative abundance of Mollicutes_RF39 at order levels was significantly reduced in benzene-exposed mice and was strongly correlated with hematopoietic indicators and urinary benzene markers. Interestingly, Mollicutes_RF39 might disturb the levels of eight metabolites, whereas Citrulline was highly linked to Mollicutes_RF39 (r=0.862, P=0.000). Consequently, Mollicutes_RF39-derived Citrulline might be the key regulator of early hematopoietic injury induced by benzene exposure. These findings promote the understanding of early hematotoxicity phenotypes and provide new perspectives on the underlying mechanisms of benzene-induced hematotoxicity.

Biological Monitoring: Evidence for Reductions in Occupational Exposure and Risk.

Aims: The aim of this publication is to explore occupational exposure trends from biological monitoring data collected over a period of more than 20 years. The data is stored within the HSE database, which holds more than 950,000 results from 120,000 workers in 8,000 companies. The data were collated for all biological monitoring results for lead, mercury, benzene, and hexamethylene diisocyanate exposures where there have been some regulatory drivers within the reported time period of the data searched. Methods: Relevant results from sample analysed were extracted from the database and categorised by year from 1996 to the end of 2019 for individual blood lead results and individual urine results for mercury, benzene, and hexamethylene diisocyanate. Results were classed by broad occupational sector where possible. Data were reported graphically by analytical biomarker result (as 90th percentile (P90)) and number of samples per year as well as with overall summary statistics. To look at longer-term trends, results were also evaluated as P90 over 6-year periods. Results: In the period 1996–2019, 37,474 blood lead, 11,723 urinary mercury, 9,188 urinary S-phenylmercapturic acid (SPMA, benzene metabolite) and 21,955 urinary hexamethylene diamine (HDA, metabolite of hexamethylene diisocyanate, HDI) samples were analysed and reported. Over the time period the blood lead concentrations saw the P90 reduce from 53 μg/dl 1996) to 24 μg/dl in 2019; the P90 urinary mercury levels reduced from 13.7 μmol/mol creatinine to 2.1 μmol/mol creatinine and the P90 urinary SPMA levels reduced from 133.7 μmol/mol creatinine to 1.7 μmol/mol creatinine. For HDI the P90 results reduced from 2 µmol HDA/mol creatinine in 1996–2000 to 0.7 in 2005–2010 but levels have since increased to 1.0 µmol HDA/mol creatinine (2016–2019). Conclusion: There is strong evidence of reductions in exposure of GB workers to lead, benzene and mercury from the data presented here. These reductions may reflect the impact of national, regional and global regulatory action to reduce exposures however, the loss of high exposure industries (from either GB as a whole or just this dataset i.e., samples are being sent elsewhere) and the increase in automation or substitution also need to be considered as potential factors. The results for HDI show that whilst interventions can reduce exposures significantly, such initiatives may need to be refreshed at intervals to maintain the reductions in exposure. We have observed that exposures move between sectors over time. Waste and recycling (lead, mercury) and tunnelling through contaminated land (benzene) were sectors or tasks associated with significant exposures and may be increasingly areas of concern.

Low-Dose Benzene Exposure Monitoring of Oil Refinery Workers: Inhalation and Biomarkers

Airborne benzene in workplaces has progressively decreased due to preventive actions and the redesigning of facility processes. Professionals who assess occupational exposure should select techniques to detect benzene levels comparable to ambient air exposure. Thus, sensitive biomarkers are needed to discriminate the effects of confounding factors, such as smoking or sorbic acid (SA). In order to identify sensitive biomarkers and to study their correlation with confounding factors, 23 oil refinery workers were enrolled in the study; their airborne benzene exposures and biomarkers were monitored. Urinary benzene (U-B), t,t-muconic acid (t,t-MA), and S-phenylmercapturic acid (SPMA) were quantified. Urinary cotinine (U-C) and t,t-sorbic acid (t,t-SA) were evaluated to flag smoking and SA intake, respectively. The benzene measured in personal inhalation sampling ranged from 0.6 to 83.5 (median 1.7) µg/m3. The concentration range of the biomarkers, U-B, t,t-MA, and SPMA, were 18–4893 ng/m3, &lt;10–79.4 µg/g creatinine, and &lt;0.5–3.96 µg/g creatinine, respectively. Pearson tests were carried out; the best correlations were between airborne benzene and U-B (µg/L r = 0.820, p &lt; 0.001) and between benzene and SPMA (g/L r = 0.812, p &lt; 0.001), followed by benzene and t,t-MA (mg/L r = 0.465, p = 0.039). From our study, U-B and SPMA result to be the most reliable biomarkers to assess the internal number of low doses of benzene exposure, thanks to their specificity and sensitivity.

Urinary metabolites as exposure biomarkers of benzene, toluene, ethylbenzene, and xylene in footwear workers and assessment of pulmonary function

Aim: This pilot cross-sectional study focused on biological monitoring of the benzene, toluene, ethylbenzene, and xylene (BTEX) urinary metabolites trans, trans-muconic acid (tt-MA), s-phenyl mercapturic acid (SPMA), hippuric acid (HA), mandelic acid (MA), and methylhippuric acid (MHA) and measured the effects of workplace BTEX exposure on pulmonary function of workers engaged in footwear manufacturing. Materials and Methods: Urinary metabolites tt-MA, SPMA, HA, MA, and MHA concentration in urine samples of study participants (N = 35) were analyzed by reverse-phase high-pressure liquid chromatography. Pulmonary function parameters were measured by spirometer and peak flow meter. Demographic information and work exposure information of study participants were collected by questionnaire interview. Results: In exposed workers, concentration of urinary SPMA, tt-MA, and HA was significantly higher (P < 0.01, in all) than the control group. Reduction in both force expiratory volume in 1 s (Forced expiratory volume in one second) and peak expiratory flow rate (PEFR) were inversely associated (P < 0.01) with growing years of age among all workers. Inverse association was measured between urinary tt-MA and decline in forced vital capacity and PEFR (P < 0.05, for each) in workers. Based on the questionnaire interview, workers were not found to be aware of workplace exposure hazards. Conclusions: Exposure biomarkers of benzene (tt-MA and SPMA) and toluene (HA) were significantly higher in workers than the control group. Study results evident the presence of occupational exposure to benzene and toluene in footwear workers. Deterioration in FEV1 and PEFR were also measured among all workers with growing years of age. The sample size was small in the present study, so further research required to confirm our results.

Benzene Exposure Analysis through S-Phenylmercapturic Acid in Urine at Platelet Levels in Footwear Workers in Sukajaya Village, Bogor Regency

BACKGROUND: Benzene is a toxic and carcinogenic compound whose presence in glue is endangering the health of workers in footwear workshops. One of its negative effects is its disruption of the bone marrow, which is where red blood cells, white blood cells, and platelets are produced. AIM: The purpose of this study was to analyze the relationship of benzene exposure with platelet levels in workers through examination of S-phenylmercapturic acid (S-PMA) concentrations in urine. METHODS: The design of the study was cross sectional, with 73 workers used as samples. The concentration of S-PMA was measured using Liquid chromatography-Mass Spectrometry/Mass Spectrometry and platelet counts using an automated hematology analyzer. Direct interview was used to retrieve workers’ individual characteristics. RESULTS: The results showed an odds ratio (OR) value of 2.28 for correlation between S-PMA concentration and platelet levels. The results also showed an OR value of 1.58 for correlation between non-routine exercise habits and platelet levels and an OR value of 1.78 for correlation between alcohol consumption and platelet levels. Multivariable logistic regression test results showed an OR of 2.59 for workers with S-PMA concentration (&gt;0.67 μg/g creatinine) on platelet counts after controlling for the variables of age and alcohol consumption. CONCLUSION: The study’s main recommendation is that information about the dangers of benzene in glue to health and how to avoid it should be disseminated to prevent benzene exposure.

Biomonitoring of the benzene metabolite s-phenylmercapturic acid and the toluene metabolite s-benzylmercapturic acid in urine from firefighters

The aim of this study was to determine firefighter’s exposure to benzene and toluene during a fire drill by monitoring air benzene and toluene, and their corresponding urinary metabolites. A liquid chromatography mass spectrometry (LC–MS) method with a minimal of sample preparation steps was developed for the benzene metabolite s-phenylmercapturic acid (SPMA) and the toluene metabolite s-benzylmercapturic acid (SBMA) in urine. Urine samples and air samples were collected from nine firefighters during and after a fire drill in a non-environmentally refurbished house. Benzene and toluene were detected in the air samples with a median concentration of 15.5 ppm and 3.2 ppm, respectively. The metabolites SPMA and SBMA was also detected in all urine samples donated ≥ three hours after the fire drill with a median concentration of 0.6 μg/g creatinine and 5.9 μg/g creatinine, respectively. By our knowledge, this is the first study detecting SPMA in urine from firefighters.

Assessment of the absorbed dose after exposure to surgical smoke in an operating room

Surgical smoke produced by electrosurgery contains various chemical substances such as volatile organic compounds (VOCs) and polycyclic aromatic hydrocarbons (PAHs). The aim of this study is to investigate airborne concentrations of VOCs and PAHs during electrosurgery in an operating room, in relation to metabolites in urine in order to assess the absorbed dose.A 5-day exposure study was set up in a general surgery operation room including surgeons, scrub assistants and circulation nurses (n = 15). Stationary and personal air sampling for VOCs and PAHs were carried out. Pre-, mid- and end-shift analysis of urinary S-phenylmercapturic acid (SPMA), o-cresol, mandelic acid and 1-hydroxypyrene was performed to assess the internal exposure to respectively benzene, toluene, styrene and PAHs.Several VOCs (styrene, ethyl benzene, benzene and toluene), ranging from 0.7 to 3.27 μg/m3 were detected in the air samples, along with one PAH (naphthalene, ranging from 0.012 to 0.39 μg/m3). There was no significant correlation between air monitoring and urinary biomonitoring. O-cresol levels were increased, especially among assistants and nurses at mid- and end-shift, exceeding current biological exposure indices several times. External and internal exposure for assistants and nurses was substantially more, compared to surgeons.This study confirms the presence of VOCs and PAHs in surgical smoke and shows the presence of their metabolites in urine, but the association is unclear. Urinary biomonitoring shows especially high concentrations of o-cresol.

Influence of benzene exposure, fat content, and their interactions on erythroid-related hematologic parameters in petrochemical workers: a cross-sectional study

BackgroundUbiquitously distributed benzene is a known hematotoxin. Increasing evidence has suggested that erythroid-related hematologic parameters may be sensitive to benzene exposure. Fat content, which is also closely associated with erythroid-related hematologic parameters, may affect the distribution and/or metabolism of benzene, and eventually benzene-induced toxicity.MethodsTo explore the influence of benzene exposure, fat content, and their interactions on erythroid-related hematologic parameters, we recruited 1669 petrochemical workers and measured their urinary S-phenylmercapturic acid (SPMA) concentration and erythroid-related hematological parameters. Indices for fat content included body fat percentage (BF%), plasma total cholesterol (TC) and triglycerides (TG), and occurrence of fatty liver.ResultsThe dose-response curve revealed U-shaped nonlinear relationships of SPMA with hematocrit (HCT) and mean corpuscular hemoglobin concentration (MCHC) (P-overall < 0.001, and P-nonlinear < 0.015), as well as positive linear associations and r-shaped nonlinear relationships of continuous fat content indices with erythroid-related hematological parameters (P-overall ≤0.005). We also observed modification effects of fat content on the associations between benzene exposure and erythroid-related hematological parameters, with workers of lower or higher BF% and TG more sensitive to benzene-induced elevation of MCHC (Pinteraction = 0.021) and benzene-induced decrease of HCT (Pinteraction = 0.050), respectively. We also found that some erythroid-related hematologic parameters differed between subgroups of workers with different SPMA levels and fat content combination.ConclusionsOur study suggested that benzene exposure, fat content, and their interactions may affect erythroid-related hematological parameters in petrochemical workers in a complex manner that are worthy of further investigation.

A SIMPLE AND SENSITIVE LC-MS/MS METHOD FOR THE DETERMINATION OF S-PHENYLMERCAPTURIC ACID IN HUMAN URINE

Benzene is an important environmental and occupational pollutant, and recognized as human carcinogen. S-phenylmercapturic acid (SPMA) is a highly specific biomarker of exposure to benzene, applied in occupational toxicology to assess low levels of benzene exposure. The objective of this study was to develop and validate a one-step liquid extraction bioanalytical method for the quantification of SPMA in urine by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The method was applied to the evaluation of benzene exposure in an occupational setting. The assay was linear from 0.5 to 500 ng mL-1 (r>0.99), accurate (91.4-105.2%) and precise, with CV% between 4.73 and 9.96%. SPMA was stable in urine for 90 days at -20 °C. Airborne benzene concentrations, urinary levels of SPMA and t,t-MA were significantly higher in gas station workers (n=30) in comparison to outdoor workers (n=14) and individuals non-occupationally exposed to benzene (n=34). Benzene airborne levels had higher correlation with urinary SPMA (r=0.532, p<0.001) than with t,t-MA (r=0.338, p=0.04), demonstrating the applicability of this biomarker for monitoring low levels of benzene exposure.

Urinary S-Phenylmercapturic Acid (S-PMA) Level and Leukocytes in Informal Shoes Industrial Workers Exposed to Benzene in Cibaduyut, Bandung Area

Urinary S-Phenylmercapturic Acid (S-PMA) Level and Leukocytes in Informal Shoes Industrial Workers Exposed to Benzene in Cibaduyut, Bandung Area

BENZENE EXPOSURE ANALYSIS IN INFORMAL SHOE INDUSTRY WORKERS IN SUKAJAYA VILLAGE, WEST JAVA VIA LEUKOCYTE COUNT AND S-PHENYLMERCAPTURIC ACID MEASUREMENT IN URINE

Background: Benzene is a hematotoxic and carcinogenic compound contained in the glue used in the shoe industry. This compound has been suspected of causing decreased leukocyte counts, which is one of the blood cell production disorders. Benzene exposure can be determined by measuring the concentration of S-phenylmercapturic acid (S-PMA) in urine.Objective: This study was conducted to determine the association between S-PMA urine concentration and the leukocyte count of shoe industry workers.Methods: The study design was cross sectional and the data were collected by conducting interviews, analyzing urine samples for S-PMA concentrations, and conducting blood examinations. Chi square and multiple logistic regression were used for the analysis.Results: The results showed there were no concentrations of S-PMA in urine that exceeded the Biological Exposure Index (BEI) value (≤25 μg/g creatinine). Higher S-PMA concentrations in this study show a higher risk of decreased leukocyte counts. When controlling for age, duration of work, history of infection, Body Mass Index (BMI), smoking, occupation, and exercise, workers with high S-PMA urine concentration were found to be at higher risk of a decreased leukocyte count.Conclusion: Although S-PMA urine concentrations were still below BEI values, workers with higher S-PMA urine concentration were more at risk of leukocyte counts of 5.0 x 103/μL. The decrease in the minimum BEI S-PMA limit value was lower than the current standard may need to be considered.

New fully automated gas chromatographic analysis of urinary S-phenylmercapturic acid in isotopic dilution using negative chemical ionization with isobutane as reagent gas.

The determination of urinary S-phenylmercapturic acid (S-PMA) represents the most reliable biomarker to monitor the intake risk of airborne benzene. Recently, the European Chemical Agency deliberated new occupational exposure limits for benzene and recommended an S-PMA biological limit value of 2-μg/g creatinine. This limit is an order of magnitude lower than the previous one, and its determination constitutes a challenge in the analytical field. We developed and validated a method that allows the fully automated and sensitive determination of S-PMA by the use of gas-chromatography negative chemical ionization tandem mass spectrometry in isotopic dilution. For negative chemical ionization, we selected a mixture of 1% isobutane in argon as reactive gas, by studying its chemical ionization mechanism and optimal parameters compared with pure isobutane or pure methane. This gas mixture produces a more abundant signal of the target analyte than isobutane or methane, and it extended the operative lifetime of the ion source, enabling us to start a high-throughput approach of the S-PMA analysis. Moreover, energy-resolved mass spectrometry experiments were carried out to refine the MS/MS analysis conditions, testing nitrogen and argon as collision gases. The method optimization was pursued by a chemometric model by using the experimental design. The quantification limit for S-PMA was 0.10 μg/L. Accuracy (between 98.3% and 99.6%) and precision (ranging from 1.6% to 6.4%) were also evaluated. In conclusion, the newly developed assay represents a powerful tool for the robust, reliable, and sensitive quantification of urinary S-PMA, and because of its automation, it is well suited for application in large environmental and biological monitoring.

Determination of seven urinary metabolites of benzene, toluene and xylene by ultra-high performance liquid chromatography-triple quadrupole mass spectrometry

Objective: To develop a method using ultra-high performance liquid chromatography-triple quadrupole mass spectrometry to determine the urinary metabolites of benzene, toluene and xylene. The selected metabolites are S-phenylmercapturic acid (S-PMA) , trans, trans-muconic acid (t, t-MA) , 8-hydroxy-2 deoxyguanosine (8-OHdG) , hippuric acid (HA) , 2-methylhippuric acid (2-MHA) , 3-methylhippuric acid (3-MHA) and 4-methylhippuric acid (4-MHA) . Methods: The urine sample was pretreated using methanol to precipitate the proteins. HSS T3 chromatographic column was used to separate the metabolites. The mass spectrometric acquisition was carried out using multiple reaction monitoring (MRM) after ionization with ESI source. External standard method was used for quantification. Results: All the standard curves showed good linear relation, and r of the seven metabolites was all above 0.999. The detection limits and quantitative limits of the seven metabolites were 0.01-500 ng/ml and 0.02-1 000 ng/ml (based on the actual dilution ratio) , respectively. The average spiked recoveries of four loadings ranged from 85.8% to 109.9%. The intra-day and inter-day precisions were 0.2%-4.5% and 0.6%-9.5%, respectively. The samples can be kept for at least 14 days at both 4 ℃ and -20 ℃. Conclusion: This method is simple, rapid and highly sensitive with low cost, and its accuracy, precision and stability can meet the daily test requirements. It can be applied for the determination of urinary S-PMA, t, t-MA, 8-OHdG, HA, 2-MHA, 3-MHA and 4-MHA for the occupational population exposed to benzene, toluene and xylene.

Benzene-induced mouse hematotoxicity is regulated by a protein phosphatase 2A complex that stimulates transcription of cytochrome P4502E1

Chronic benzene exposure is associated with hematotoxicity and the development of aplastic anemia and leukemia. However, the signaling pathways underlying benzene-induced hematotoxicity remain to be defined. Here, we investigated the role of protein phosphatase 2A (PP2A) in the regulation of benzene-induced hematotoxicity in a murine model. Male mice with a hepatocyte-specific homozygous deletion of the Ppp2r1a gene (encoding PP2A Aα subunit) (HO) and matched wildtype (WT) mice were exposed to benzene via inhalation at doses of 1, 10, and 100 ppm for 28 days. Peripheral white blood cell counts and activation of bone marrow progenitors were attenuated in the HO mice, indicating that Ppp2r1a deletion protects against benzene-induced hematotoxicity. Moreover, elevation of urinary S-phenyl mercapturic acid, a benzene metabolite, was much greater in WT mice than in HO mice. Real-time exhalation analysis revealed more exhaled benzene but fewer benzene metabolites in HO mice than in WT mice, possibly because of the down-regulation of Cyp2e1, encoding cytochrome P4502E1, in hepatocytes of the HO mice. Loss-of-function screening disclosed that PP2A complexes containing the B56α subunit participate in regulating Cyp2e1 expression. Notably, PP2A-B56α suppression in HepG2 cells resulted in persistent β-catenin phosphorylation at Ser33-Ser37-Thr41 in response to CYP2E1 agonists. In parallel, nuclear translocation of β-catenin was inhibited, concomitant with a remarkable decrease of Cyp2e1 expression. These findings support the notion that a regulatory cascade comprising PP2A-B56α, β-catenin, and Cyp2e1 is involved in benzene-induced hematotoxicity, providing critical insight into the role of PP2A in responses to the environmental chemicals.

Environmental exposure to benzene: evaluation of urinary S-PMA and polymorphism (CYP2E1-1293G&gt;C and NQO1 609C&gt;T) in Campos Elíseos residents, Duque de Caxias, Rio de Janeiro State, Brazil

Benzene is one of the most important substances for assessment, due to its significant use, the environmental contamination resulting from its emission and the effects on human health. It is classified by the International Agency for Research on Cancer (IARC) as a known carcinogen to humans (group 1) and associated with the development of leukemia. In general, the population is exposed to this substance by inhaling contaminated air, which varies according to the location and intensity of its potential sources. The petrochemical industry is one of the most important sources of this compound. The municipality of Duque de Caxias, specifically the Campos Elíseos district, in Rio de Janeiro State, Brazil, houses the Industrial Complex of Campos Elíseos (PICE), a grouping of over 25 industries, which includes the second largest oil refinery in Brazil. Environmental contamination from the PICE has been recognized, but there is a lack of studies concerning its impact on the health of the surrounding population. S-phenylmercapturic acid (S-PMA) concentrations ranging from 0.80 to 8.01μg.g-1 creatinine were observed in the local population, apparently related to hematological changes also observed in exposed population. The quantifiable presence of urinary S-PMA from the benzene metabolism is associated with the fact that 60% of the participants present specific hematological changes, which may be due to the environmental benzene exposure. The allele and genotype frequencies of the CYP2E1 and NQO1 enzymes observed in the study population were similar to those reported in other studies. The presence of the variant allele in the NQO1 genotype may be a risk factor for the observed hematological changes.

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

Previous studies have demonstrated that oxidative stress is implicated in benzene-induced hematotoxicity. However, the low dose-response effects and the mechanism underlying perturbation of hematopoiesis remain to be defined. This study aims to address the role of Nrf2 pathway in mediating benzene-induced hematotoxicity. Nrf2+/+ (wildtype, Nrf2-WT) and Nrf2−/− (knockout, Nrf2-KO) mice were administrated with benzene at doses of 0.1, 1.0, 10.0, 100.0 mg/kg by oral gavage for a consecutive 4 weeks (6 times/week). As a result, benzene exposure caused a decline of WBC and lymphocyte counts in a dose-dependent manner at a dose range from 1.0 to 100.0 mg/kg, while low dose benzene induced hormesis effects. Interestingly, Nrf2 deficiency seemed to relieve the decline of peripheral blood cell counts upon benzene exposure, indicating the involvement of Nrf2 in regulation of benzene-induced hematotoxicity. The suppression of phase II enzyme expression in Nrf2-KO mice resulted in considerable reduction in detoxification indicated by the decrease of urinary S-phenylmercapturic acid (SPMA), a metabolite of benzene. Ex vivo assay revealed enhanced cytotoxicity and oxidative stress were induced by benzene in Nrf2-KO mice. Notably, the depletion of Nrf2 triggered the proliferation and differentiation of hematopoietic cells, but induced aberrant morphological changes in periphery erythrocytes and bone marrow cells, implicating the compensatory effects carried on at the expense of induction of dysfunctional blood cells. Our findings provide a new insight into a low dose–response towards benzene-induced hematotoxicity and uncover the critical role of Nrf2 pathway in mediating abnormal hematopoiesis in response to oxidative stress.

Biomonitoring of Benzene and Effect of Wearing Respirators during an Oil Spill Field Trial at Sea

The main aim of this study was to assess the biological uptake of benzene and polycyclic aromatic hydrocarbons (PAHs) for subjects exposed to fresh crude oil released at sea. The study included 22 subjects participating in an 'oil-on-water' field trial in the North Sea. Over 2 consecutive days, there were six releases with two different types of fresh crude oils. Exposed subjects (n = 17) were either located in small, open-air boats downwind and close to the released oil (<50 m) or on the main deck of two large vessels further from the released oil (100-200 m). Subjects assumed to be unexposed (n = 5) were located indoors on the command bridge of either vessel. Full-shift personal benzene exposure was monitored with passive thermal desorption tubes (ATD-tubes) packed with Tenax TA and subsequent gas chromatographic analysis. Urine samples were collected before and after work-shift on both days and analyzed for urinary markers of benzene [(S-phenylmercapturic acid (SPMA)] and PAHs [1-hydroxypyrene (1-OH)]. Information about the use of personal protective equipment, smoking habits, location, work tasks, and length of work-shift were recorded by a questionnaire. Subjects located in the small boats downwind and close to the released oil were exposed to relatively high concentrations of benzene (arithmetic mean = 0.2 ppm, range 0.002-1.5 ppm) compared to the occupational exposure limits (OELs) for 8 h (1 ppm) and 12 h (0.6 ppm). Although respirators were available to all exposed subjects, SPMA was detected in post-shift urine (0.5-3.3 µmol mol-1) of five exposed subjects reporting not wearing respirators, all located in the small boats downwind and close to the released oil. For exposed subjects wearing respirators (n = 12), the post-shift urinary SPMA was below the detection limit (0.8 µmol mol-1) even when the benzene exposure exceeded the OELs. Urinary levels of PAH were within the reference range of what is considered as background levels (<0.4 µmol mol-1). During the initial stages of a bulk oil spill at sea, when the evaporation of benzene is at its highest, it is important to use appropriate respirators to prevent biological uptake of benzene.