Low-Dose, Occupational Exposure to the Leukemogen Benzene Induces Robust Changes in the Blood Transcriptome Associated with Altered Immune System Biology.

Abstract

Benzene, a common industrial solvent and ubiquitous environmental contaminant, is hematotoxic and chronic exposure increases the risk of leukemia and lymphoma. Benzene is also immunotoxic and has been shown to increase susceptibility to infectious agents. Benzene depresses B and T lymphocyte numbers as well as their mitogenic responses and benzene metabolites mediate the impairment of macrophage activity. The immunotoxic effects of benzene have been demonstrated mainly in animal and in vitro models exposed to high levels of benzene or its metabolites. In order to elucidate the molecular mechanisms underlying the hematotoxic and immunotoxic effects of benzene, we previously performed a global gene expression study of a small number of workers (N = 6) exposed to benzene (>10ppm) compared with unexposed controls (N = 6), and identified several genes associated with benzene exposure. Here, we greatly expanded the study to include 125 individuals exposed to a range of benzene concentrations, including 59 individuals exposed to <1ppm benzene. Using microarrays, we analyzed the peripheral blood mononuclear cell (PBMC) transcriptomes of these low-exposed Chinese shoe-factory workers for differential gene expression compared with controls (N = 42) matched by gender, age, and socioeconomic status. Exposure to other solvents including toluene, were minimal and we adjusted for exposure to cigarette smoke. After adjusting for multiple comparisons by controlling the false discovery rate (FDR), the microarray analysis revealed that 2355 genes (represented by 2488 probes), were significantly dysregulated by low-dose occupational benzene exposure (FDR q-values < 0.05), with 1590 genes (1663 probes) having FDR q-values <0.01. Although the fold-changes of the significant genes ranged between 0.65 and 3.36-fold, the majority of genes were modestly altered by benzene, with only 248 genes up- or down-regulated by more than 30 %. The findings demonstrate that low-dose benzene exposure causes widespread subtle, yet highly significant, perturbation of gene expression in PBMC. Gene Ontology analysis of the 248 genes up- or down-regulated by more than 30 %, revealed an overrepresentation of genes involved in the immune (N = 46, p = 1.64E-21), defense (N = 33, p = 3.21E-13) and inflammatory responses (N = 25, p = 6.46E-13), and apoptosis (N = 23, p = 1.14E-04). Analysis of all 2355 significant genes, regardless of fold-change, showed that basic cellular processes, such as translation, were impacted. Specific pathways affected by low-dose benzene exposure included the Cytokine-Cytokine Receptor interaction (p = 7.90E-11), Toll-like receptor signaling (p = 1.66E-06), T cell receptor signaling (p = 1.05E-03), and apoptosis (p = 3.94E-03) pathways. Our study also included individuals exposed to high levels of benzene (>10 ppm; N = 13), analysis of which revealed differential expression of 1538 genes (1604 probes), compared with controls (FDR q-values < 0.05). Functions and pathways similar to those observed at low-dose exposures were identified among these genes. Our findings to date suggest that even relatively low levels of occupational benzene exposure cause a significant perturbation of immune system biology.