Effects of low concentrations of benzene on human lung cells in vitro

Benzene exposure and risk of lung cancer in the Norwegian Offshore Petroleum Worker cohort: a prospective case-cohort study

OBJECTIVE

The objective of our study was to examine whether occupational exposure to benzene is associated with lung cancer among males in the Norwegian Offshore Petroleum Workers cohort.

METHODS

Among 25 347 male offshore workers employed during 1965-1998, we conducted a case-cohort study with 399 lung cancer cases diagnosed between 1999 and 2021, and 2035 non-cases sampled randomly by 5-year birth cohorts. Individual work histories were coupled to study-specific job-exposure matrices for benzene and other known lung carcinogens. Weighted Cox regression was used to estimate HRs and 95% CIs for the associations between benzene exposure and lung cancer, by major histological subtypes, adjusted for age, smoking and occupational exposure to welding fumes, asbestos and crystalline silica. Missing data were imputed.

RESULTS

For lung cancer (all subtypes combined), HRs (95% CIs) for the highest quartiles of benzene exposure versus unexposed were 1.15 (0.61 to 2.35) for cumulative exposure, 1.43 (0.76 to 2.69) for duration, and 1.22 (0.68 to 2.18) for average intensity (0.280≤P-trend≤0.741). For 152 adenocarcinoma cases, a positive trend was observed for exposure duration (P-trend=0.044).

CONCLUSIONS

In this cohort of offshore petroleum workers generally exposed to low average levels of benzene, we did not find an overall clear support for an association with lung cancer (all subtypes combined), although an association was suggested for duration of benzene exposure and adenocarcinoma. The limited evidence might be due to restricted statistical power.

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

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

Herbicide Widespread: The Effects of Pethoxamid on Nonalcoholic Fatty Liver Steatosis In Vitro

Pethoxamid is a widespread herbicidal product, presenting itself as an extremely flexible active substance and with a high potential for use as an herbicide for preemergence. The emergence of multiple resistance in crops has been addressed using combinations of preemergence and postemergence herbicides in the same seeding-harvest cycle. A winning combination of pethoxamid and glyphosate mainly affected the acidobacteria population. Glyphosate scientific literature has demonstrated an observational link between herbicide exposure and liver disease in human subjects. Identifying and ranking the risk to the public that pethoxamid could exert on target organs has not been evaluated so far. Due to similarities to glyphosate, we did look at the effect of pethoxamid on impaired liver cells HepG2, using a nonalcoholic fatty liver disease (NAFLD) cell model in vitro. Pethoxamid was cytotoxic starting at 1 ppm. Fatty acid accumulation (FA) was enhanced while low doses of pethoxamid slightly decreased LDH protein expression compared to FA-treated HepG2. The same trend was observed for cytochrome c. Based on our data, we can argue that NAFLD hepatic cells react to pethoxamid trying detoxifying strategies, ready to undergo cell death to avoid further degeneration. Downregulation of cytochrome can lead to the hypothesis that pethoxamid should not induce herbicide resistance.

Interaction effects of environmental response gene polymorphisms and benzene exposure on telomere length in shoe-making workers

Benzene is a globally occurring environmental and occupational pollutant that causes leukemia. To better understand telomere length (TL) as a function of benzene toxicity, we recruited 294 shoe-making workers and 102 controls from Wenzhou, China in 2011. Biomarkers of TL, cytokinesis-block micronucleus (MN) frequency, and white blood cells (WBC) were measured. In total, 18 polymorphic sites in environmental response genes, including metabolic and DNA repair genes, were analyzed. Results indicate that benzene exposure led to a longer TL at a threshold of 32 mg/m³-year of cumulative exposure dose (CED). Furthermore, the TL was longer in members of the damaged group, when evaluated for MN frequency (P < 0.001) and reduced WBC (P < 0.001), than in those of the normal group. Workers carrying genotype TT (β = 0.32, P = 0.042) in rs3212986 of ERCC1 and genotype TC (β = 0.24, P = 0.082) in rs1051740 of mEH exon3 were associated with a longer TL as compared to the wild-type group. TA (β = -0.53, P < 0.001) in rs6413432 of CYP2E1 was associated with a shorter TL. Benzene exposure interacted with the TA type in rs6413432 (β = 0.003, 95% CI: 0, 0.006, P = 0.042) and the CC type in rs1051740 (β = 0.007, 95% CI: 0.001, 0.013, P = 0.015) after adjusting for confounding factors. Our results indicate that benzene induces an increase in TL at a threshold of CED ≥32mg/m³-year. Rs1051740, rs3212986, and rs6413432 were found to be involved in benzene-induced telomere growth; in particular, rs1051740 and rs6413432 interacted with the benzene exposure, resulting in an extended TL.

The effect of malondialdehyde is modified by simian virus 40 transformation in human lung fibroblast cells

The effects of malondialdehyde (MDA), a product of oxidative stress, on normal lung fibroblast cells (MRC5) and transformed cells (MRC5 SV2) showed differing responses between the two cell lines. MRC5 cells showed lower viability at low MDA concentrations (<250 μM) but had better viability at higher concentrations than the transformed cells. Both cell lines showed an increase in the number of micronuclei, nuclear size and a relocation of p53 to the nucleus with increasing MDA. The expression of p53 was higher in the MRC5 cells at 24 h; 2-8 fold induction vs 1-2.5 fold in the MRC5 SV2 cells, but reduced to almost zero at 48 h in the MRC5 cells. Mutation sequencing of the PCR products of a 689 bp region (residues 4640-5328) of the TP53 gene revealed MRC5 had more mutations than MRC5 SV2 cells (n = 21 and 11 respectively) and that they were predominantly insertions (MRC5 81%, MRC5 SV2 100%). A common mutation was observed in both cell lines; a G insertion at residue 4724 (n = 7) which could prove to be a mutational hotspot. These results indicate that the transformed cells are slower to respond to oxidative stress and/or mutagenic compounds. The mutation spectrum of predominantly frameshift mutations (insertions) suggests that oxidative stress plays a minimal role in smoking related lung cancer, but could be of greater importance to other lung diseases and cancer caused by exposures such as passive smokers, passive vapers and atmospheric pollutants.

Environmental Factors Impacting Bone-Relevant Chemokines

Chemokines play an important role in normal bone physiology and the pathophysiology of many bone diseases. The recent increased focus on the individual roles of this class of proteins in the context of bone has shown that members of the two major chemokine subfamilies-CC and CXC-support or promote the formation of new bone and the remodeling of existing bone in response to a myriad of stimuli. These chemotactic molecules are crucial in orchestrating appropriate cellular homing, osteoblastogenesis, and osteoclastogenesis during normal bone repair. Bone healing is a complex cascade of carefully regulated processes, including inflammation, progenitor cell recruitment, differentiation, and remodeling. The extensive role of chemokines in these processes and the known links between environmental contaminants and chemokine expression/activity leaves ample opportunity for disruption of bone healing by environmental factors. However, despite increased clinical awareness, the potential impact of many of these environmental factors on bone-related chemokines is still ill defined. A great deal of focus has been placed on environmental exposure to various endocrine disruptors (bisphenol A, phthalate esters, etc.), volatile organic compounds, dioxins, and heavy metals, though mainly in other tissues. Awareness of the impact of other less well-studied bone toxicants, such as fluoride, mold and fungal toxins, asbestos, and chlorine, is also reviewed. In many cases, the literature on these toxins in osteogenic models is lacking. However, research focused on their effects in other tissues and cell lines provides clues for where future resources could be best utilized. This review aims to serve as a current and exhaustive resource detailing the known links between several classes of high-interest environmental pollutants and their interaction with the chemokines relevant to bone healing.

BTEX in vitro exposure tool using human lung cells: trips and gains

Cytotoxicity of benzene, toluene, ethylbenzene and xylenes (BTEX) to human lung cells was explored using three different exposure methods: Method 1 - in normal 96-well plates using DMSO as a carrier vehicle, we exposed (a) human lung carcinoma A549 cells, (b) A549 cells over-expressed with cytochrome P450 2E1 cells, and (c) normal lung fibroblast LL-24 cells to benzene, toluene, ethylbenzene and xylene individually and in a mixture which models car exhaust gases for between 1-88 h. We found that the order of the BTEX potency is benzene<toluene<ethylbenzene=m-xylene with acute BTEX toxicity to A549≈LL-24>CYP2E1 over-expressed A549 cells. A significant difference was found between inter-assay responses for all 24h exposures (P<0.005) suggesting a poor assay repeatability. No sign of potency increase was found from 6 to 72 h exposures. Method 2 - Using sealed vials to expose A549 cells to benzene, toluene and ethylbenzene, we observed a twenty-fold increase in their cytotoxicity, but also with no time-course effect. Method 3 - Using air exposed hanging-drop cell culture, we were able to see both an increase of demonstration of toxicity and a time-course effect from 1 to 12h exposure. We conclude that exposing cells in sealed and unsealed media using DMSO as a carrier vehicle was not suitable for BTEX exposure studies. Hanging-drop air exposure has more potential. It should be noted that if there are any changes in their exposure matrixes, its exposure mass distribution in cells could differ.

Alterations in leukocyte telomere length in workers occupationally exposed to benzene

Exposure to benzene, a known leukemogen and probable lymphomagen, has been demonstrated to result in oxidative stress, which has previously been associated with altered telomere length (TL). TL specifically has been associated with several health outcomes in epidemiologic studies, including cancer risk, and has been demonstrated to be altered following exposure to a variety of chemical agents. To evaluate the association between benzene exposure and TL, we measured TL by monochrome multiplex quantitative PCR in 43 workers exposed to high levels of benzene and 43 age and sex-matched unexposed workers in Shanghai, China. Benzene exposure levels were monitored using organic vapor passive dosimetry badges before phlebotomy. The median benzene exposure level in exposed workers was 31 ppm. The mean TL in controls, workers exposed to levels of benzene below the median (≤31 ppm), and above the median (>31 ppm) was 1.26 ± 0.17, 1.25 ± 0.16, and 1.37 ± 0.23, respectively. Mean TL was significantly elevated in workers exposed to >31 ppm of benzene compared with controls (P = 0.03). Our findings provide evidence that high levels of occupational benzene exposure are associated with TL. Environ.

How benzene and its metabolites affect human marrow derived mesenchymal stem cells

Benzene is a known environmental pollutant with demonstrated leukemogenic activity. Marrow mesenchymal stem cells (MSCs), contribute to skeletal remodeling and repair. They also support haematopoiesis constructing important elements of haematopoietic niche. In the present study, the effects of a range of benzene concentrations along with those of its reactive metabolites, p-benzoquinone (BQ) and hydroquinone (HQ) on the viability of MSCs, apoptosis induction and caspase3/7 activity in these cells were analyzed. Our findings revealed that low concentrations of these chemicals (10μM of benzene, 5μM of either of BQ or HQ) significantly increase the number of chemically treated cells. Moreover, applied BQ/HQ concentrations were shown to be able to considerably inhibit caspase3/7 activity. While in benzene exposure experiments, the lowest concentration triggered the greatest increase in caspase3/7 activity during the initial hours of exposure. On the other hand, MSCs exposure to higher concentrations of benzene (100μM) and its metabolites, BQ/HQ (10μM and 50μM), can induce cell death after 24h of exposure mainly through apoptotic pathways. In addition, changes in the expression of six mRNAs due to being subjected to 10μM of BQ or HQ and 50μM of benzene were assessed. The genes under investigation were RUNX2, WNT5A, DKK1, JAG1, KITLG and CXCL12 which are expressed by MSCs playing roles in adipo-osteogenic differentiation of MSCs and the regulation of haematopoiesis. The analysis exhibited a great augmentation in RUNX2 expression associated with DKK1 and KITLG up-regulation. The results also indicated that treatment of cells with all three chemicals gives rise to down-regulation of JAG1 and treatment with both HQ and BQ triggers WNT5A over-expression. With regard to CXCL12, treatment with BQ caused slight up-regulation and treatment with HQ led to down-regulation. The alterations observed in the expression profile of genes could affect/modify the process of differentiation of MSCs into osteoblast. Other expected outcomes involve augmented canonical Wnt signaling activity in exposed cells with RUNX2 overexpression as the indicator which is probably forced to decrease to the normal level via DKK1 and WNT5A up-regulation. RUNX2 overexpression in MSCs can also be indicative of the RUNX2 up-regulation in myeloid progenitors thereby its involvement in AML development due to benzene exposure. Observed changes in the expression of WNT5A, DKK1, KITLG, CXCL12 and JAG1 can lead to the disturbance of HSC niche resulting in haematopoietic failure and leukemia development. It is obvious that increased viability together with caspase3/7 inhibition could aggravate the adverse effects of exposure to these chemicals.

An alternative gas-phase in vitro exposure system for toxicity testing: the interaction between nitrous oxide and A549 cells

An original in vitro approach was adopted to expose cells to volatile agents. The anaesthetic nitrous oxide (N(2)O) was chosen as the model agent, and type II pneumocyte-like cells (A549 cells) were used as the target to represent the lungs. A time-lapse microscopy station was equipped with a manual gas mixer that allowed the generation of a mixture of N(2)O/air/CO(2) in the gas phase, to provide a uniform distribution of the volatile agent. The dissolution of N(2)O in the culture medium was monitored by gas chromatography-electron capture detection. Biochemical alterations, in terms of homocysteine accumulation, demonstrated that intracellular methionine synthase had been inactivated by N(2)O absorbed by the cells, a process that also occurs in vivo. Toll-like receptors, which are key molecules in inflammatory lung diseases, were also investigated at the molecular level. Our experiments indicated that biochemical and molecular alterations occurred in the cells, even under conditions where neither morphologic changes nor consistent alterations in cell proliferation were evident. This in vitro exposure system can be efficiently adopted for looking at the repeat-dose effects of volatile agents on respiratory tissues. Moreover, it could be of further benefit for identifying the wide range of specific cell targets, and for monitoring relevant endpoints in the cellular and molecular processes that occur during exposure to volatile compounds.

Benzene induces cytotoxicity without metabolic activation

OBJECTIVES

Benzene has been consistently associated with hematological disorders, including acute myeloid leukemia and aplastic anemia, but the mechanisms causing these disorders are still unclear. Various metabolites of benzene lead to toxicity through the production of reactive oxygen species (ROS), the inhibition of topoisomerase and DNA damage. However, benzene itself is considered to have no mutagenic or cytotoxic activity. In this study, we investigated the effects of benzene itself on a human myeloid cell line with or without benzene metabolizing enzyme inhibitors.

METHODS

A human myeloid cell line, HL-60, was exposed to benzene with or without cytochrome P450 2E1 or myeloperoxidase inhibitor. Cytotoxicity was evaluated in terms of global DNA methylation levels, induction of apoptosis, and ROS production.

RESULTS

Benzene did not change global DNA methylation levels. However, benzene itself increased the levels of apoptosis and ROS. This cytotoxicity did not change with the addition of benzene metabolizing enzyme inhibitors. Benzene itself increased the mRNA levels of oxidative stress-related genes and transcription factors of activator protein-1.

CONCLUSIONS

Benzene did not influence global DNA methylation in HL-60 cells, but had cytotoxic effects and changed gene expression levels. To elucidate the mechanisms of benzene toxicity, benzene itself as well as benzene metabolites must be investigated.