Global Gene Expression Response in Peripheral Blood Cells of Petroleum Workers Exposed to Sub-Ppm Benzene Levels

Review on novel toxicological effects and personalized health hazard in workers exposed to low doses of benzene

Several recent reports indicate health hazards for workers with below occupational limit exposure to benzene (BZ). Our updated review indicates that such low exposures induced traditional as well as novel toxicity/genotoxicity, e.g., increased mitochondria copy numbers, prolongation of telomeres, impairment of DNA damage repair response (DDRR), perturbations of expression in non-coding RNAs, and epigenetic changes. These abnormalities were associated with alterations of gene expression and cellular signaling pathways which affected hematopoietic cell development, expression of apoptosis, autophagy, etc. The overarching mechanisms for induction of health risk are impaired DDRR, inhibition of tumor suppressor genes, and changes of MDM2-p53 axis activities that contribute to perturbed control for cancer pathways. Evaluation of the unusual dose-responses to BZ exposure indicates cellular over-compensation and reprogramming to overcome toxicity and to promote survival. However, these abnormal mechanisms also promote the induction of leukemia. Further investigations indicate that the current exposure limits for workers to BZ are unacceptable. Based on these studies, the new exposure limits should be less than 0.07 ppm rather than the current 1 ppm. This review also emphasizes the need to conduct appropriate bioassays, and to provide more reliable decisions on health hazards as well as on exposure limits for workers. In addition, it is important to use scientific data to provide significantly improved risk assessment, i.e., shifting from a population- to an individual-based risk assessment.

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

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

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

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

Benzene-associated immunosuppression and chronic inflammation in humans: a systematic review

OBJECTIVE

Recent evidence has accumulated that the immune system is intimately intertwined with cancer development. Two key characteristics of carcinogens in which the immune system plays a central role are chronic inflammation and immunosuppression. In this systematic review, we investigated the association of chronic inflammatory and immunosuppressive outcomes with benzene, a widely used industrial chemical. Benzene has been confirmed to cause acute myeloid leukaemia and suspected to cause non-Hodgkin lymphoma, two cancers of the blood-forming system that affect immune cells.

METHODS

We systematically searched PubMed and Embase for all relevant studies using a combination of Medical Subject Headings (MeSH) and selected key words. The detailed review protocol, including search strategy, was registered with PROSPERO, the international prospective register of systematic reviews (#CRD42019138611).

RESULTS

Based on all human studies selected in the final review, we report new evidence of a benzene-induced immunosuppressive effect on the adaptive immune system and activation of the innate immune system to cause inflammation. In particular, benzene significantly lowers the number of white blood cells, particularly lymphocytes such as CD4+ T-cells, B-cells and natural killer cells, and increases proinflammatory biomarkers at low levels of exposure.

CONCLUSION

To the best of our knowledge, this is the first comprehensive review of benzene's immunotoxicity in humans. Based on results obtained from this review, we propose two potential immunotoxic mechanisms of how benzene induces leukaemia/lymphoma: (1) cancer invasion caused by proinflammatory cytokine production, and (2) cancer promotion via impaired immunosurveillance. Further studies will be required to confirm the connection between benzene exposure and its effects on the immune system.

5'UTR methylation in different genes from workers exposed to volatile organic compounds: A new insight for considering an epigenetic mark as a functional correlate

Gene-specific methylation has been related with transcriptional/translational consequences in different cells; also, this epigenetic modification is affected by environmental exposures. In previous studies, CYP2E1 activity in toluene-exposed workers was decreased compared to controls, however, CYP2E1 promoter methylation levels did not show significant differences. Here, we compared gene-specific methylation levels at the 5'UTR region, in a subset of workers whom already participated in two former studies, compared to controls.

METHODS

DNA was obtained from whole blood in five different groups: occupationally exposed to a mixture of volatile organic compounds (VOC): high levels (n = 19); low levels (n = 19) and very low levels (n = 17), toluene-exposed workers (n = 19) and control group (n = 19). We performed PCR-pyrosequencing at the 5'UTR region from four genes: CYP2E1, IL-6, SOD1 and TNF-α.

RESULTS

In participants exposed to high levels of a VOC mixture, we found significant differences: lower methylation levels for IL-6, and higher methylation levels for TNF-α compared to controls. In toluene-exposed workers, we found significant, lower methylation levels for CYP2E1 compared to controls.

CONCLUSION

Lower methylation levels at the 5'UTR region from CYP2E1 in toluene exposed-workers, suggests that this epigenetic modification could represent a functional correlate regarding enzymatic activity, as a response to toluene biotransformation.

Epimedium polysaccharides attenuates hematotoxicity by reducing oxidative stress and enhancing immune function in mice model of benzene-induced bone marrow failure

Chronic benzene (BZ) exposure is associated with multiple adverse health effects and leads to progressive bone marrow failure (BMF). BZ-induced BMF is an acquired aplastic anemia characterized by severe anemia, neutropenia and thrombocytopenia, which is likely caused by immunotoxicity and oxidative stress. Previous studies showed that Epimedium polysaccharides (EPS), a natural and major herbal compound derived from Epimedium, has immunomodulatory and antioxidant potential. The purpose of this study was to evaluate the potential efficacy of EPS against BZ-induced BMF. BMF mouse model was established by subcutaneous injection of 2 ml/kg BZ in CD1 mice. Mice received daily oral treatment with 100 mg/kg high-dose EPS and 20 mg/kg low-dose EPS for four weeks. Our data showed that EPS treatment alleviated BZ-associated weight loss and increased the number of whole blood cells in peripheral blood and nucleated cells in bone marrow. Furthermore, EPS treatment decreased apoptotic rate and reactive oxygen species production, S-phase arrest in bone marrow cells. Finally, EPS treatment improved T cell-mediated immune suppression by increasing CD3+, CD4 + T-cell counts, and CD4+/CD8+ ratio. and modulated hematopoietic cytokines including EPO, IL-11, and IL-2 in peripheral blood. Our study suggests that EPS is a potential therapeutic target to attenuate hematotoxicity induced by BZ.