Evaluation of genotoxicity in workers exposed to benzene and atmospheric pollutants

The Comet Assay as a Tool in Human Biomonitoring Studies of Environmental and Occupational Exposure to Chemicals-A Systematic Scoping Review

Biomonitoring of human populations exposed to chemical substances that can act as potential mutagens or carcinogens, may enable the detection of damage and early disease prevention. In recent years, the comet assay has become an important tool for assessing DNA damage, both in environmental and occupational exposure contexts. To evidence the role of the comet assay in human biomonitoring, we have analysed original research studies of environmental or occupational exposure that used the comet assay in their assessments, following the PRISMA-ScR method (preferred reporting items for systematic reviews and meta-analyses extension for scoping reviews). Groups of chemicals were designated according to a broad classification, and the results obtained from over 300 original studies (n = 123 on air pollutants, n = 14 on anaesthetics, n = 18 on antineoplastic drugs, n = 57 on heavy metals, n = 59 on pesticides, and n = 49 on solvents) showed overall higher values of DNA strand breaks in the exposed subjects in comparison with the unexposed. In summary, our systematic scoping review strengthens the relevance of the use of the comet assay in assessing DNA damage in human biomonitoring studies.

Brazilian workers occupationally exposed to different toxic agents: A systematic review on DNA damage

The evaluation of genotoxicity in workers exposed to different toxic agents is very important, especially considering the association between these exposures in a chronic context and DNA damage. Assessing biomarkers of exposure and, when possible, early biomarkers of effect, contributes to elucidating the potential toxic mechanisms involved in genotoxicity and its contribution to chronic non-communicable diseases. In Brazil, the biggest country in South America, workers are exposed to hazardous physical and chemical agents. Considering that these exposures occur, in most cases, throughout the worker's whole life, this is an important public health concern in Brazil. Therefore, this systematic review aims to analyze occupational exposure to chemical and physical agents and the association with DNA damage in studies carried out in Brazil from 1980 to 2021. A systematic and comprehensive literature search was performed in different databases based on occupational exposure to chemical and physical agents and DNA damage. Only full articles on studies that investigated experimental evidence on occupational exposure in Brazil and assessed DNA damage were included, amounting to 89 articles. Five main occupational exposure groups were identified: pesticides (36%), organic solvents (20%), dust and particles (16%), metals (11%), and ionizing radiation (6%). Another group called "others" included studies (11%) that did not fall into these main groups. It was found that comet assay and micronucleus tests are the most adopted methods to detect DNA damage. Occupational exposures were most associated with DNA damage. However, further improvements in study design would be needed to better characterize the association between biomonitoring and DNA damage, particularly to account for confounding factors.

Levamisole, a cocaine cutting agent, induces acute and subchronic systemic alterations in Wistar rats

The use of the anthelmintic levamisole as a cocaine adulterant has been increasing worldwide. Complications caused by this association include systemic vasculitis, agranulocytosis, neutropenia, tissue necrosis, pulmonary hemorrhage, and renal injury. Data about toxicity of levamisole are scarce, therefore the aim of this study was to evaluate the acute and subchronic toxic effects of levamisole in rats. Male Wistar rats received saline or levamisole by intraperitoneal route at the doses of 12, 24 and 36 mg/kg in the acute toxicity test; and at 3, 6 and 12 mg/kg in the subchronic toxicity test. Toxicity was evaluated using behavioral, cognitive, renal, hematological, biochemical and histopathological parameters. Acute administration of levamisole caused behavioral and histopathological alterations. Subchronic administration caused behavioral, cognitive and hematological alterations (p < 0.0001 and p < 0.05, respectively), impairment of liver and kidney functions (p < 0.05), and changes of antioxidant defenses (p ≤ 0.0001). Both administrations produced toxic effects of clinical relevance, which make levamisole a dangerous cutting agent. Furthermore, the knowledge of these effects can contribute to the correct diagnosis and treatment of cocaine dependents with unusual systemic alterations.

A new method to predict genotoxic effects based on serum molecular profile

It is critical to develop new methods to assess genotoxic effects in human biomonitoring since the conventional methods are usually laborious, time-consuming, and expensive. It is aimed to evaluate if the analysis of a drop of serum by Fourier Transform Infrared spectroscopy, allow to assess genotoxic effects in occupational exposure to cytostatic drugs in hospital professionals, as obtained by the lymphocyte cytokinesis-block micronucleus assay. It was considered peripheral blood from hospital professionals exposed to cytostatic drugs (n = 22) and from a non-exposed group (n = 36). It was observed that workers occupationally exposed presented a higher number of micronuclei (p < 0.05) in lymphocytes, in relation to the non-exposed group. The serum Fourier Transform Infrared spectra from exposed workers presented diverse different peaks (p < 0.01) in relation to the non-exposed group. The hierarchical cluster analysis of serum spectra separated serum samples of the exposed group from the non-exposed group with 61% sensitivity and 88% specificity. A support vector machine model of serum spectra enables to predict exposure with high accuracy (0.91), precision (0.89), sensitivity (0.86), F1 score (0.87) and AUC (0.96). Therefore, Fourier Transform Infrared spectroscopic analysis of a drop of serum enabled to predict in a rapid and simple mode the genotoxic effects of cytostatic drugs. The method presents therefore potential for high-dimension screening of exposure of genotoxic substances, due to its simplicity and rapid setup mode.

Biomarkers of Low-Level Environmental Exposure to Benzene and Oxidative DNA Damage in Primary School Children in Sardinia, Italy

Background: The main anthropic sources of exposure to airborne benzene include vehicular traffic, cigarette smoke, and industrial emissions. Methods: To detect early genotoxic effects of environmental exposure to benzene, we monitored environmental, personal, and indoor airborne benzene in children living in an urban area and an area near a petrochemical plant. We also used urinary benzene and S-phenylmercapturic acid (S-PMA) as biomarkers of benzene exposure and urinary 8-hydroxydeoxyguanosine (8-OHdG) as a biomarker of early genotoxic effects. Results: Although always below the European Union limit of 5 μg/m³, airborne benzene levels were more elevated in the indoor, outdoor, and personal samples from the industrial surroundings compared to the urban area (p = 0.026, p = 0.005, and p = 0.001, respectively). Children living in the surroundings of the petrochemical plant had urinary benzene values significantly higher than those from the urban area in both the morning and evening samples (p = 0.01 and p = 0.02, respectively). Results of multiple regression modelling showed that age was a significant predictor of 8-OHdG excretion, independent of the sampling hour. Moreover, at the low exposure level experienced by the children participating in this study, neither personal or indoor airborne benzene level, nor personal monitoring data, affected 8-OHdG excretion. Conclusions: Our results suggest the importance of biological monitoring of low-level environmental exposure and its relation to risk of genotoxic effects among children.

Occupational exposure assessment in professionals who manipulate and administer antineoplastic drugs in a university hospital in Southern Brazil

INTRODUCTION

Our goal was to demonstrate the effects of occupational exposure to antineoplastic drugs on oxidative stress parameters and DNA damage in health professionals who manipulate and administer antineoplastic drugs in a University Hospital in Southern Brazil.

METHODS

The case-control study with a longitudinal design, involved 64 individuals, 29 of them pharmacists, pharmacy technicians and nurses who were occupationally exposed to antineoplastic drugs and 35 professionals who were not exposed. Gene mutations were determined by micronucleus from salivary fluid; DNA damage by comet assay and oxidative stress parameters in whole blood were also evaluated.

RESULTS

All workers exposed to antineoplastic drugs used personal protective equipment (PPE). It was demonstrated that the total nonprotein thiol and thiobarbituric acid reactive substances levels showed interaction between group and time, with higher levels one week after handling/administration of antineoplastic drugs in the exposed group (GEE, p ≤ 0.0001 and p = 0,013, respectively). Additionally, there was a group effect on the activities of the catalase and glutathione peroxidase antioxidant enzymes (GEE, p = 0.027 and p ≤ 0.0001, respectively), and workers occupationally exposed to antineoplastic drugs had higher enzyme activities compared to those not exposed. No genotoxic damage was demonstrated through the evaluated parameters.

CONCLUSIONS

Despite the correct use of PPE, professionals occupationally exposed to antineoplastic drugs were more susceptible to oxidative stress than those not exposed. The evaluation of the studied parameters is especially important for the definition of conducts and practices in the area, always in search of guaranteeing the establishment of a rational policy to protect workers' health.

Sintocalmy, a Passiflora incarnata Based Herbal, Attenuates Morphine Withdrawal in Mice

Chronic opioid use changes brain chemistry in areas related to reward processes, memory, decision-making, and addiction. Both neurons and astrocytes are affected, ultimately leading to dependence. Passiflora incarnata L. (Passifloraceae) is the basis of frequently used herbals to manage anxiety and insomnia, with proven central nervous system depressant effects. Anti-addiction properties of P. incarnata have been reported. The aim of this study was to investigate the effect of a commercial extract of Passiflora incarnata (Sintocalmy®, Aché Laboratory) in the naloxone-induced jumping mice model of morphine withdrawal. In addition, glial fibrillary acidic protein (GFAP) and S100 calcium-binding protein B (S100B) levels were assessed in the frontal cortex and hippocampus, and DNA damage was verified on blood cells. In order to improve solubilization a Sintocalmy methanol extract (SME) was used. SME is mainly composed by flavonoids isovitexin and vitexin. The effects of SME 50, 100 and 200 mg/kg (i.p.) were evaluated in the naloxone-induced withdrawal syndrome in mice. SME 50 and SME 100 mg/kg decreased naloxone-induced jumping in morphine-dependent mice without reducing locomotor activity. No alterations were found in GFAP levels, however SME 50 mg/kg prevented the S100B increase in the frontal cortex and DNA damage. This study shows anti-addiction effects for a commercial standardized extract of P. incarnata and suggests the relevance of proper clinical assessment.

Derivation of an occupational exposure limit for benzene using epidemiological study quality assessment tools

This paper derives an occupational exposure limit for benzene using quality assessed data. Seventy-seven genotoxicity and 36 haematotoxicity studies in workers were scored for study quality with an adapted tool based on that of Vlaanderen et al., 2008 (Environ Health. Perspect. 116 1700-5). These endpoints were selected as they are the most sensitive and relevant to the proposed mode of action (MOA) and protecting against these will protect against benzene carcinogenicity. Lowest and No- Adverse Effect Concentrations (LOAECs and NOAECs) were derived from the highest quality studies (i.e. those ranked in the top tertile or top half) and further assessed as being "more certain" or "less certain". Several sensitivity analyses were conducted to assess whether alternative "high quality" constructs affected conclusions. The lowest haematotoxicity LOAECs showed effects near 2 ppm (8 h TWA), and no effects at 0.59 ppm. For genotoxicity, studies also showed effects near 2 ppm and showed no effects at about 0.69 ppm. Several sensitivity analyses supported these observations. These data define a benzene LOAEC of 2 ppm (8 h TWA) and a NOAEC of 0.5 ppm (8 h TWA). Allowing for possible subclinical effects in bone marrow not apparent in studies of peripheral blood endpoints, an OEL of 0.25 ppm (8 h TWA) is proposed.

Human CYP2E1-dependent mutagenicity of benzene and its hydroxylated metabolites in V79-derived cells: Suppression and enhancement by ethanol pretreatment

Benzene is a human carcinogen that requires metabolic activation. We previously observed that benzene and its hydroxylated metabolites induce micronuclei in mammalian cells expressing human CYP2E1. This study was initially aimed to study another endpoint, the induction of gene mutations by those compounds in the same cell models. A V79-derived cell line expressing human CYP2E1 and sulfotransferase (SULT) 1A1 (V79-hCYP2E1-hSULT1A1) pretreated with ethanol (a CYP2E1 stabilizer) was used in the hprt gene mutagenicity assay. Phenol, hydroquinone, catechol, and 1,2,4-trihydroxybenzene all induced gene mutations, while they were inactive, or only weakly positive (hydroquinone), in parental V79-Mz cells. Unexpectedly, benzene was non-mutagenic in both cell lines, but it became positive in V79-hCYP2E1-hSULT1A1 cells using regimes of short exposure/long recovery without ethanol pretreatment, for both gene mutations and micronuclei formation. In silico molecular simulation showed binding energies and positions favorable for each compound to be oxidized by human CYP2E1, benzene demonstrating the highest affinity. By tunnel analysis, ethanol binding did not limit benzene to pass tunnel S, which was specifically active for benzene. However, its end product, acetic acid, decreased the occurrence of tunnel S from 5.4 to 2.2% and extended the length of its bottleneck from 5.5 to 9.0 Å. With residual ethanol molecules still being present in CYP2E1 for a period of time after benzene exposure, the acetic acid formed could limit the entrance of benzene, thus inhibit its metabolic activation. In summary, ethanol may interfere with the activation of benzene to mutagenic metabolites, at least in cultured cells.

Biomarkers of exposure, effect, and susceptibility in occupational exposure to traffic-related air pollution: A review

There is a well-recognized association between environmental air pollution exposure and several human diseases. However, the relationship between diseases related to occupational air pollution exposure on roads and high levels of traffic-related air pollutants (TRAPs) is less substantiated. Biomarkers are essential tools in environmental and occupational toxicology, and studies on new biomarkers are increasingly relevant due to the need to determine early biomarkers to be assessed in exposure conditions. This review aimed to investigate the main advances in the biomonitoring of subjects occupationally exposed to air pollution, as well as to summarize the biomarkers of exposure, effect, and susceptibility. Furthermore, we discuss how biomarkers could be used to complement the current application of methods used to assess occupational exposures to xenobiotics present in air pollution. The databases used in the preparation of this review were PubMed, Scopus, and Science Direct. Considering the significant deleterious effects on health associated with chronic occupational exposure to xenobiotics, this topic deserves attention. As it is difficult to avoid occupational exposure to TRAPs, biomonitoring should be applied as a strategy to reduce the toxic effects of workplace exposure.

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

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

The prevalence and persistence of aberrant promoter DNA methylation in benzene-exposed Chinese workers

Aberrant DNA methylation patterns are common in cancers and environmental pollutant exposed subjects. Up to date, few studies have examined the aberrant DNA methylation patterns in benzene exposed workers. We recruited 141 benzene-exposed workers, including 83 benzene-exposed workers from a shoe factory in Wenzhou and 58 workers from a painting workshop in Wuhu, 35 workers in Wuhu were followed from 2009 to 2013, and 48 indoor workers as controls from Wenzhou. We used high-resolution melting (HRM) to quantitate human samples of DNA methylation in long interspersed nuclear element-1 (LINE-1), (6)-methylguanine-DNA methyltransferase (MGMT), and DNA mismatch repair gene human mutator L homologue 1 (hMLH1). AML-5 cells were treated with benzoquinone (BQ) and hydroquinone (HQ), and the promoter methylation of MGMT and hMLH1 was detected using the bisulfite sequencing PCR method. The degree of LINE-1 methylation in benzene-exposed workers was significantly lower than that of the controls (p<0.001), and the degree of MGMT (p<0.001) and hMLH1 (p = 0.01) methylation was significantly higher than that of the controls. The in vitro study validated the aberrant hypermethylation of hMLH1 after treatment with BQ. Among the cohort workers who were followed from 2009 to 2013, the LINE1 methylation elevated in 2013 than 2009 (p = 0.004), and premotor methylation in hMLH1 reduced in 2013 than 2009 (p = 0.045) with the reduction of the benzene exposure. This study provides evidence that benzene exposure can induce LINE-1 hypomethylation and DNA repair gene hypermethylation.

Environmental Assessment and Evaluation of Oxidative Stress and Genotoxicity Biomarkers Related to Chronic Occupational Exposure to Benzene

Environmental and occupational exposure to benzene from fuels is a major cause for concern for national and international authorities, as benzene is a known carcinogen in humans and there is no safe limit for exposure to carcinogens. The objective of this study was to evaluate the genotoxic effects of chronic occupational exposure to benzene among two groups of workers: filling station workers (Group I) and security guards working at vehicles entrances (Group II), both on the same busy highway in Rio de Janeiro, Brazil. Sociodemographic data on the workers were evaluated; the concentration of benzene/toluene (B/T) in atmospheric air and individual trans,trans-muconic acid (ttMA) and S-phenylmercapturic acid (S-PMA) were measured; oxidative stress was analyzed by catalase (CAT), glutathione S-transferase (GST), superoxide dismutase (SOD), thiol groups (THIOL) and malondialdehyde (MDA); genotoxicity was measured by metaphases with chromosomal abnormalities (MCA) and nuclear abnormalities, comet assay using the enzyme formamidopyrimidine DNA glycosylase (C-FPG), and methylation of repetitive element LINE-1, CDKN2B and KLF6 genes. Eighty-six workers participated: 51 from Group I and 35 from Group II. The B/T ratio was similar for both groups, but Group I had greater oscillation of benzene concentrations because of their work activities. No differences in ttMA and S-PMA, and no clinical changes were found between both groups, but linearity was observed between leukocyte count and ttMA; and 15% of workers had leukocyte counts less than 4.5 × 10⁹ cells L^-1, demanding close worker's attention. No differences were observed between the two groups for THIOL, MDA, MCA, or nuclear abnormalities. A multiple linear relationship was obtained for the biomarkers MCA and C-FPG. A significant correlation was found between length of time in current job and the biomarkers C-FPG, MCA, GST, and MDA. Although both populations had chronic exposure to benzene, the filling station workers were exposed to higher concentrations of benzene during their work activities, indicating an increased risk of DNA damage.

The role of B7 costimulation in benzene immunotoxicity and its potential association with cancer risk

Benzene is a recognized human carcinogen; however, there are still some gaps in the knowledge regarding the mechanism of toxicity of this organic solvent and potential early biomarkers for the damage caused by it. In a previous study, our research group demonstrated that the adhesion molecules of the immune system (B7.1 and B7.2) could be potential biomarkers in the early detection of immunotoxicity caused by benzene exposure. Therefore, this study was developed to deepen the understanding regarding this important topic, aiming to contribute to the comprehension of the benzene toxicity mechanism mediated by B7.1 and B7.2 and its potential association with the risk of carcinogenicity. B7.1 and B7.2 protein expression in blood monocytes and B7.1 and B7.2 gene expression in PBMCs were evaluated. Additionally, complement C3 and C4 levels in serum were measured, as well as p53 gene expression in PBMCs. Seventy-four gas station workers (GSW group) and 71 non-occupationally exposed subjects (NEG) were evaluated. Our results demonstrated decreased levels of B7.1 and B7.2 protein and gene expression in the GSW group compared to the NEG (n = 71) (p < 0.01). Along the same lines, decreased levels of the complement system were observed in the GSW group (p < 0.01), demonstrating the impairment of this immune system pathway as well. Additionally, a reduction was observed in p53 gene expression in the GSA group (p < 0.01). These alterations were associated with both the benzene exposure biomarker evaluated, urinary trans, trans-muconic acid, and with exposure time (p < 0.05). Moreover, strong correlations were observed between the gene expression of p53 vs. B7.1 (r = 0.830; p < 0.001), p53 vs. B7.2 (r = 0.685; p < 0.001), and B7.1 vs. B7.2 (r = 0.702; p < 0.001). Taken together, these results demonstrate that the immune system co-stimulatory molecule pathway is affected by benzene exposure. Also, the decrease in p53 gene expression, even at low exposure levels, reinforces the carcinogenicity effect of benzene in this pathway. Therefore, our results suggest that the promotion of immune evasion together with a decrease in p53 gene expression may play an important role in the benzene toxicity mechanism. However, further and targeted studies are needed to confirm this proposition.

Hair straightening products and the risk of occupational formaldehyde exposure in hairstylists

Hair straitening products are widely used by hairstylists. Many keratin-based hair smoothing products contain formaldehyde. This study aimed to investigate occupational formaldehyde exposure among hairstylists dealing with hair straightening products and the relation between genotoxicity biomarkers and the short-term formaldehyde exposure concentrations and the working years. The study was carried out in Cairo, Egypt on 60 hairstylists use hair straightening products divided into two groups according to the working years. All hairstylists were subjected to micronucleus (MN) frequencies in both epithelial buccal cells (EBC) and peripheral blood lymphocytes (PBL). Fifteen-minute (min) formaldehyde exposure concentrations were measured at workplace during hair straightening procedure. Fifteen-minute formaldehyde concentrations in both groups exceeded the National Institute for Occupational Safety and Health and the American Conference of Governmental Industrial Hygienist thresholds levels. The MN frequencies in EBC and PBL showed a significant increase in group II in comparison to control and group I, which in turn showed a significant increase in MN frequency in PBL and a nonsignificant increase in the MN frequency in EBC when compared to control. A positive correlation was found between genotoxicity biomarkers and working years. Occupational exposures to hair straightening products in the studied hairstylist were found to expose them to formaldehyde concentrations that exceeded the standard limits. All selected genotoxicity biomarkers showed a significant increase in exposed workers and were positively correlated to the duration of exposure.

The use of genotoxicity biomarkers in molecular epidemiology: applications in environmental, occupational and dietary studies

Molecular epidemiology is an approach increasingly used in the establishment of associations between exposure to hazardous substances and development of disease, including the possible modulation by genetic susceptibility factors. Environmental chemicals and contaminants from anthropogenic pollution of air, water and soil, but also originating specifically in occupational contexts, are potential sources of risk of development of disease. Also, diet presents an important role in this process, with some well characterized associations existing between nutrition and some types of cancer. Genotoxicity biomarkers allow the detection of early effects that result from the interaction between the individual and the environment; they are therefore important tools in cancer epidemiology and are extensively used in human biomonitoring studies. This work intends to give an overview of the potential for genotoxic effects assessment, specifically with the cytokinesis blocked micronucleus assay and comet assay in environmental and occupational scenarios, including diet. The plasticity of these techniques allows their inclusion in human biomonitoring studies, adding important information with the ultimate aim of disease prevention, in particular cancer, and so it is important that they be included as genotoxicity assays in molecular epidemiology.

8-Hydroxydeoxyguanosine as a biomarker of oxidative DNA damage in workers exposed to low-dose benzene

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Gasoline station attendants have higher urinary t,t,-MA and 8-OHdG levels.

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There is strong correlation between 8-OHdG and benzene exposure level.

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8-OHdG levels are significantly correlated also with job seniority.

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Low-level chronic exposure to benzene can determine oxidative damage on DNA.

The present study aims to investigate the relation between exposure to low-dose benzene and the occurrence of oxidative DNA damage in gasoline station workers, as well as the possible role of interfering or confounding factors.

Urine levels of 8-OHdG were evaluated by a competitive immunoassay in a group of 80 men, employed in gasoline stations located in East Sicily and compared with a control group (n = 63) of male office employees not occupationally exposed to benzene. Information regarding socio-demographic characteristics, lifestyle and job-related records were provided through a questionnaire.

Significantly higher (p < 0.05) urinary t,t,-MA and 8-OHdG levels were observed in gasoline station attendants compared to subjects not exposed to benzene.

Pearson’s test demonstrated a strong correlation (r = 0.377, p < 0.001) between 8-OHdG and benzene exposure level. 8-OHdG significantly correlated also with job seniority, (r = 0.312, p < 0.01), whereas the relation with age resulted weaker (r = 0.242, p < 0.05). Multiple linear regression analysis, performed to exclude a role for confounding factors, showed that variables like gender, smoking habit, alcohol consumption and BMI did not have a significant influence on the measured biomarkers. No subject enrolled in the study presented signs or symptoms of work-related disease or other illness linked to oxidative stress.

These results suggest that low-level chronic exposure to benzene among gasoline station attendants can determine oxidative damage on DNA, as indicated by alteration of 8-OHdG which may represent a non-invasive biomarker of early genotoxic damage in exposed subjects.

DNA damage in the elderly is associated with 5-MTHF levels: a pro-oxidant activity

The aging phenomenon is associated with oxidative stress damage in biomolecules, especially DNA. 5-Methyltetrahydrofolate (5-MTHF), the active folate form, plays a pivotal role in maintaining genomic integrity. However, recently it was associated with cancer development. In Brazil, there are folic acid enriched foods, such as flour, making the general population chronically exposed to folates. Therefore, the aim of this study was to investigate whether erythrocytes 5-MTHF levels were associated with age-related DNA damage in two groups (elderly and young subjects). Additionally, a study in Caenorhabditis elegans, an in vivo alternative model, was performed to verify if 5-MTHF presents a pro-oxidant effect. A total of 50 elderly and 25 young subjects participated in this study, which analyzed whole blood DNA damage, plasma carbonyl proteins (PCO), and erythrocytes 5-MTHF levels. In addition, ROS and RNS production, survival rate, and lifespan were performed in C. elegans exposed to 5-MTHF. Blood 5-MTHF levels and DNA damage were increased in the elderly compared to the young group. A positive association was found between 5-MTHF levels and DNA damage, and between DNA damage and PCO levels, suggesting an oxidative cause of damage associated with the active folate form. In an experimental study it was observed that 5-MTHF increased ROS production in C. elegans, in a dose dependent manner, while survival rate and life span were not affected at the test doses. These findings suggest that 5-MTHF, the active folate form, may be involved in DNA damage in the elderly. This damage could be a result of oxidative stress, as observed in the in vivo alternative model; however, more studies are necessary to prove our present results.

Environmental exposure to human carcinogens in teenagers and the association with DNA damage

BACKGROUND

We investigated whether human environmental exposure to chemicals that are labeled as (potential) carcinogens leads to increased (oxidative) damage to DNA in adolescents.

MATERIAL AND METHODS

Six hundred 14-15-year-old youngsters were recruited all over Flanders (Belgium) and in two areas with important industrial activities. DNA damage was assessed by alkaline and formamidopyrimidine DNA glycosylase (Fpg) modified comet assays in peripheral blood cells and analysis of urinary 8-hydroxydeoxyguanosine (8-OHdG) levels. Personal exposure to potentially carcinogenic compounds was measured in urine, namely: chromium, cadmium, nickel, 1-hydroxypyrene as a proxy for exposure to other carcinogenic polycyclic aromatic hydrocarbons (PAHs), t,t-muconic acid as a metabolite of benzene, 2,5-dichlorophenol (2,5-DCP), organophosphate pesticide metabolites, and di(2-ethylhexyl) phthalate (DEHP) metabolites. In blood, arsenic, polychlorinated biphenyl (PCB) congeners 118 and 156, hexachlorobenzene (HCB), dichlorodiphenyltrichloroethane (DDT) and perfluorooctanoic acid (PFOA) were analyzed. Levels of methylmercury (MeHg) were measured in hair. Multiple linear regression models were used to establish exposure-response relationships.

RESULTS

Biomarkers of exposure to PAHs and urinary chromium were associated with higher levels of both 8-OHdG in urine and DNA damage detected by the alkaline comet assay. Concentrations of 8-OHdG in urine increased in relation with increasing concentrations of urinary t,t-muconic acid, cadmium, nickel, 2,5-DCP, and DEHP metabolites. Increased concentrations of PFOA in blood were associated with higher levels of DNA damage measured by the alkaline comet assay, whereas DDT was associated in the same direction with the Fpg-modified comet assay. Inverse associations were observed between blood arsenic, hair MeHg, PCB 156 and HCB, and urinary 8-OHdG. The latter exposure biomarkers were also associated with higher fish intake. Urinary nickel and t,t-muconic acid were inversely associated with the alkaline comet assay.

CONCLUSION

This cross-sectional study found associations between current environmental exposure to (potential) human carcinogens in 14-15-year-old Flemish adolescents and short-term (oxidative) damage to DNA. Prospective follow-up will be required to investigate whether long-term effects may occur due to complex environmental exposures.

Micronucleus, Nucleoplasmic Bridge, and Nuclear Budding in Peripheral Blood Cells of Workers Exposed to Low Level Benzene

BACKGROUND

Benzene is one of the important occupational pollutants. There are some reports about the leukemogenic effects related to low-level exposure to benzene.

OBJECTIVE

To study the frequency of micronucleus (MN), nucleoplasmic bridge (NB), and nuclear budding (NBUD) in the peripheral blood lymphocytes of petrochemical workers with low level exposure to benzene.

METHODS

We enrolled 50 workers exposed to low-level benzene and 31 unexposed workers of a petrochemical industry. After exclusion of 3 samples, peripheral blood lymphocytes of the remaining 47 exposed and 31 unexposed workers were analyzed for the frequency of MN, NB, and NBUD by cytochalasin-blocked MN technique.

RESULTS

MN was present in 28 (60%) exposed and 18 (58%) unexposed workers. NB was observed in 6 (13%), and 2 (7%) exposed and unexposed workers, respectively; the frequency for NBUD was 20 (43%), and 13 (42%), respectively. No significant difference was found in the observed frequencies of MN, NB, and NBUD in the peripheral blood lymphocytes between the exposed and unexposed group workers.

CONCLUSION

Occupational exposure to low-level benzene does not increase the frequency of MN, NB, and NBUD in the peripheral blood lymphocytes, biomarkers for DNA damage.

Gaseous benzene degradation by photocatalysis using ZnO + Zn2TiO4 thin films obtained by sol-gel process

The benzene pollutant in gaseous phase was successfully degraded by using ZnO + Zn2TiO4 multicomponent oxide thin films as photocatalysts. The films were obtained with different Ti/Zn ratios (0, 0.20, 0.40, 0.45, 0.50, 0.67, 0.84, and 1) by the sol-gel route. The initial level of benzene concentration was 110 ± 10 ppm. The process was carried out under different conditions of relative humidity (RH): 25, 50, and 80 % in a batch-type reactor, at room temperature. The results show benzene degradation near to 95 % at t = 240 min, where the multicomponent oxide semiconductor has a Ti/Zn ratio of 0.67. Meanwhile, with the TiO2 thin films, only a degradation of 70 % was reached at the same measurement conditions. This synergistic effect on the photocatalytic activity is a result of the coupling of both semiconductor oxides. An adverse effect on the photocatalytic activity was observed as the relative humidity increases.

DNA damage and repair capacity in workers exposed to low concentrations of benzene

DNA damage and cellular repair capacity were studied in 18 male fuel tanker drivers and 13 male filling-station attendants exposed to low and very low concentrations of benzene, respectively, and compared to 20 males with no occupational exposure (controls). Exposure to airborne benzene was measured using passive personal samplers, and internal doses were assayed through the biomarkers t,t-muconic acid, S-phenylmercapturic acid and urinary benzene. DNA damage was evaluated using tail intensity (TI) determined by the comet assay in peripheral lymphocytes. Urinary 7-hydro-8-oxo-2'-deoxyguanosine (8-oxodG) was measured as a biomarker of oxidative damage. DNA repair kinetics were assessed using the comet assay in lymphocytes sampled 20 and 60 min post H2O2 exposure. Benzene exposure differed significantly between the drivers (median 246.3 µg/m(3)), attendants (median 13.8 µg/m(3)), and controls (median 4.1 µg/m(3)). There were no differences in TI and 8-oxodG among the three groups, or between smokers and non-smokers. DNA repair kinetics were similar among the drivers, attendants and controls, although the comet assay on H2 O2 -damaged lymphocytes after 60 min revealed significantly lower levels of TI only in drivers. The DNA repair process in smokers was similar to that observed in drivers. In conclusion, this study found no relationship between low levels of benzene exposure and DNA damage, although there was evidence that exposure interferes with DNA repair kinetics. The biological impact of this finding on the onset of genotoxic effects in exposed workers has still to be ascertained.

Overexpression of G6PD and HSP90 Beta in Mice with Benzene Exposure Revealed by Serum Peptidome Analysis

The small peptides representation of the original proteins are a valuable source of information that can be used as biomarkers involved in toxicity mechanism for chemical exposure. The aim of this study is to investigate serum peptide biomarkers of benzene exposure. C57BL/6 mice were enrolled into control group and benzene groups of 150 and 300 mg/kg/d Serum peptides were identified by mass spectrometry using an assisted laser desorption ionization/time of flight mass spectrometry (MS). Differential peptide spectra were obtained by tandem mass spectrometry and analyzed by searching the International Protein Index using the Sequest program. Forty-one peptide peaks were found in the range of 1000-10,000 Da molecular weight. Among them, seven peaks showed significantly different expression between exposure groups and control group. Two peptide peaks (1231.2 and 1241.8), which showed a two-fold increase in expression, were sequenced and confirmed as glucose 6-phosphate dehydrogenase (G6PD) and heat shock protein 90 Beta (HSP90 Beta), respectively. Furthermore, the expression of the two proteins in liver cells showed the same trend as in serum. In conclusion, G6PD and HSP90 beta might be the candidate serum biomarkers of benzene exposure. It also provided possible clues for the molecular mechanism of benzene-induced oxidative stress.