Benzene, a major industrial chemical and environmental pollutant, causes a variety of hematological disorders in man, including aplastic anemia, myelodysplastic syndrome, and acute myelogenous leukemia. While it is clear that benzene must be metabolized to cause its acute hematotoxic effects, no single metabolite of benzene reproduces these effects in vivo. Coadministration of hydroquinone (HQ) and phenol (PHE), however, does lead to bone marrow suppression in rodents. A pharmacokinetic interaction between these two benzene metabolites results in increased concentrations of both metabolites in bone marrow. Peroxidase and/or phenoxy-radical mediated oxidation of HQ then initiates redox cycling and formation of the reactive electrophile, 1,4-benzoquinone, which is considered the ultimate hematotoxic metabolite of benzene. However, 1,4-benzoquinone readily undergoes glutathione (GSH) conjugation to form 2-(glutathion-S-yl)hydroquinone, 2,5-bis-(glutathion-S-yl)hydroquinone, 2,6-bis-(glutathion-S-yl)hydroquinone, and 2,3,5-tris-(glutathion-S-yl)hydroquinone. Preliminary data indicate that these GSH conjugates are present in the bone marrow of rats and mice following coadministration of hydroquinone and phenol. Moreover, the majority of HQ-GSH conjugates present in bone marrow are formed in situ and are metabolized to more reactive thiol conjugates via a previously unidentified mercapturic acid pathway. Because these quinol-thioether metabolites have enhanced capability to both redox cycle and arylate tissue macromolecules, we hypothesize that quinol-thioether metabolites contribute to benzene-mediated hematotoxicity and that the mechanism(s) likely involve the production of reactive oxygen species and/or interaction with proteins that specifically recognize GSH/cysteine and GSH/cysteine containing molecules. Such metabolite specific interactions interfere with growth- and differentiation-related signaling. We therefore propose to (i) assess the acute hematotoxicity of HQ-GSH conjugates in rodent hematopoietic tissue, (ii) determine changes in the production and/or function of hematopoietic growth factors in response to HQ-GSH conjugates, (iii) test the hypothesis that metabolite-induced changes in gamma-glutamyl transpeptidase activity (GGT), dipeptidase activity, cysteine transport, and GSH concentrations, precipitate sphingolipid turnover, the generation of ceramide and the induction of apoptosis, and (iv) test the hypothesis that specific proteins involved in the synthesis (GST), transport (GS-X pump), and metabolism (GGT, dipeptidases) of the peptidyl leukotrienes are targets of HQ-GSH conjugates and interfere with granulocytic cell differentiation. Because benzene reduces the number of myeloid stem cells in bone marrow and induces incomplete granulocytic differentiation, our studies will provide a comprehensive understanding of the mechanisms by which reactive polyphenolic metabolites of benzene cause perturbations in growth- and differentiation-related signaling and how such changes culminate in benzene-mediated hematotoxicity.
| Monks, Terrence J; Butterworth, Michael; Lau, Serrine S (2010) The fate of benzene-oxide. Chem Biol Interact 184:201-6 |
