Prevention of benzene-induced myelotoxicity and prostaglandin synthesis in bone marrow of mice by inhibitors of prostaglandin H synthase

Administration of benzene to mice causes bone marrow toxicity and elevations in prostaglandin E2 (PGE2), a negative regulator of myelopoiesis. In these experiments, benzene (400 mg/kg; 2 x/day for 2 days) administered to DBA/2 or C57Bl/6 mice decreased bone marrow cellularity and myeloid progenitor cell development (measured as colony-forming units per femur) by 40%. When inhibitors of the cyclooxygenase component of prostaglandin H synthase (PHS) (either indomethacin, 2 mg/kg; aspirin, 50 mg/kg; meclofenamate, 4 mg/kg) were coadministered with benzene, myelotoxicity and the elevation in bone marrow PGE level were prevented. Additionally, when indomethacin (1 microM) was added to cultures of bone marrow cells from benzene-treated mice, myeloid progenitor cell development was the same as the controls. The doses of indomethacin used had no affect on the hepatic conversion of benzene to its major metabolite, phenol. Using purified PHS, indomethacin (10 microM) inhibited the arachidonic acid-dependent oxidation of hydroquinone to p-benzoquinone, a putative reactive metabolite of benzene. Indomethacin (10 microM) had no effect on the H2O2-driven oxidation of hydroquinone catalysed by either PHS-peroxidase or myeloperoxidase. Coadministration of the benzene metabolites, phenol and hydroquinone, has been reported previously to reproduce the myelotoxicity of benzene. In our studies, phenol and hydroquinone (50 mg/kg each; 2 x/day for 2 days) decreased bone marrow cellularity by 40%; however, coadministration of indomethacin (2 mg/kg) or meclofenamate (4 mg/kg) with these metabolites did not prevent the decrease in bone marrow cell number. Our results implicate marrow PHS in mediating the short-term myelotoxicity of benzene.