Aryl Hydrocarbon Receptor Mediates Benzene-Induced Hematotoxicity

Abstract

Benzene can induce hematotoxicity and leukemia in humans and mice. Since a review of the literature shows that the CYP2E1 knockout mouse is not known to possess any benzene toxicity, the metabolism of benzene by CYP2E1 in the liver is regarded to be prerequisite for its cytotoxicity and genotoxicity, although the mechanism is not fully understood yet. Because it was found some years ago that benzene was also a substrate for CYP1A1, we investigated the involvement of the aryl hydrocarbon receptor (AhR) in benzene hematotoxicity using AhR wild-type (AhR(+/+)), heterozygous (AhR(+/-)), and homozygous (AhR(-/-)) male mice. Interestingly, following a 2-week inhalation of 300 ppm benzene (a potent dose for leukemogenicity), no hematotoxicity was induced in AhR(-/-) mice. Further, there were no changes in cellularity of peripheral blood and bone marrow (BM), nor in levels of granulocyte-macrophage colony-forming units in BM. This lack of hematotoxicity was associated with the lack of p21 overexpression, which was regularly seen in the wild-type mice following benzene inhalation. Combined treatment with two major benzene metabolites, phenol and hydroquinone, induced hemopoietic toxicity, although it was not known whether this happened due to a surprising lack of expression of CYP2E1 by AhR knockout, or due to a lack of other AhR-mediated CYP enzymes, including 1A1 (i.e., a possible alternative pathway of benzene metabolism). The former possibility, evaluated in the present study, failed to show a significant relationship between AhR and the expression of CYP2E1. Furthermore, a subsequent evaluation of AhR expression after benzene inhalation tended to show higher but less significant expression in the liver, and none in the BM, compared with sham control. Although this study failed to identify the more likely of the above-mentioned two possibilities, the study using AhR knockout mice on benzene inhalation presents the unique possibility that the benzene toxicity may be regulated by AhR signaling.

Mechanisms of benzene-induced hematotoxicity and leukemogenicity: cDNA microarray analyses using mouse bone marrow tissue.

“…A particular expression change in the aryl hydrocarbon receptor (AhR) was observed for which a mechanism could not be specified (data not shown). As we previously observed, sensitivity to benzene toxicity is innate in AhR-KO mice, implying that AhR transmits this sensitivity to benzene toxicity (Yoon et al 2002).…”

“…The total RNA yielded optical density (OD) ratios (OD 260/280) of 1.7-2.1; its purity was confirmed by gel On the days marked with an asterisk (*), both sham exposure mice were killed at 4 P.M., and exposed mice were killed immediately after exposure (Yoon et al 2002). On D+3, both sham and recovery mice were killed at 4 P.M. D5 designates practically a 1-week exposure and D12, a 2-week exposure.…”

Pathogenesis of Aryl Hydrocarbon Receptor-Mediated Development of Lymphoma Is Associated with Increased Cyclooxygenase-2 Expression

“…Primer sequences are listed in Table 1. DNAfree total RNA (0.01 to 1.0 g) was reverse-transcribed using 4 U of Omniscript reverse transcriptase (Qiagen) and 1 g of oligo(dT) 15 in a final volume of 40 l. The primers for each gene were designed on the basis of the respective cDNA or mRNA sequences using OLIGO primer analysis software, provided by Steve Rosen and Whitehead Institute/Massachusetts Institute of Technology Center for Genome Research, Cambridge, MA. PCR amplification was performed in a total volume of 20 l, containing 2 l of cDNA, 10 l of 2ϫ Fast Real-Time SYBR Green PCR master mix, and 0.2 mol/L of each primer.…”

“…The involvement of an AhR-mediated pathway has been implicated in animal models demonstrating benzene-induced leukemia. 15 Activation of the AhR in the absence of exogenous ligands has been described in T-cell leukemia cells and lymphoma cells. 16,17 A hallmark of leukemic/lymphoma cells is the ability to proliferate in the absence of exogenous growth factors and to escape apoptosis.…”

Effects Of Benzene on Human Hematopoiesis

“…Alternative mechanisms, involving oncogene activation such as c-Myb [122] and aryl hydrocarbon receptor activation [123,124], have been proposed to be involved in benzene-induced hematotoxicity. Aryl hydrocarbon receptor activation by benzene metabolites suggests biological effects of benzene at low doses.…”