macrophages , an important cell - type of the bone marrow stroma , are possible targets of benzene toxicity because they contain relatively large amounts of prostaglandin h synthase ( phs ) , which is capable of metabolizing phenolic compounds to reactive species . 
 phs also catalyzes the production of prostaglandins , negative regulators of myelopoiesis . 
 studies indicate that the phenolic metabolites of benzene are oxidized in bone marrow to reactive products via peroxidases . with respect to macrophages , 
 phs peroxidase is implicated , as in vivo benzene - induced myelotoxicity is prevented by low doses of nonsteroidal anti - inflammatory agents , drugs that inhibit phs . 
 incubations of either 14c - phenol or 14c - hydroquinone with a lysate of macrophages collected from mouse peritoneum ( greater than 95% macrophages ) , resulted in an irreversible binding to protein that was dependent upon h2o2 , incubation time , and concentration of radiolabel . 
 production of protein - bound metabolites from phenol or hydroquinone was inhibited by the peroxidase inhibitor aminotriazole . 
 protein binding from 14c - phenol also was inhibited by 8 microm hydroquinone , whereas binding from 14c - hydroquinone was stimulated by 5 mm phenol . 
 the nucleophile cysteine inhibited protein binding of both phenol and hydroquinone and increased the formation of radiolabeled water - soluble metabolites . 
 similar to the macrophage lysate , purified phs also catalyzed the conversion of phenol to metabolites that bound to protein and dna ; this activation was both h2o2- and arachidonic acid - dependent . 
 these results indicate a role for macrophage peroxidase , possibly phs peroxidase , in the conversion of phenol and hydroquinone to reactive metabolites and suggest that the macrophage should be considered when assessing the hematopoietic toxicity of benzene.imagesfigure 9.figure 10 .