PEROXIDASE-ACTIVITY IN MURINE AND HUMAN HEMATOPOIETIC PROGENITOR CELLS - POTENTIAL RELEVANCE TO BENZENE-INDUCED TOXICITY

Peroxidases may be important in the mechanism of toxicity of a number of compounds including benzene, a chemical that has been associated wi th bone marrow toxicity and leukemia after chronic exposure. The major peroxidase in bone marrow is myeloperoxidase (MPO), which has been pr eviously thought to be expressed at the promyelocytic stage of differe ntiation. Hematopoietic progenitor cells are important potential cellu lar targets of bone marrow toxins and leukemogens. We therefore examin ed peroxidase activity in both murine and human progenitor cells. Muri ne progenitor populations were purified as lineage-negative cells (>99 % enriched) and human progenitor populations were purified as CD34(+) cells (>95% enriched). Using conventional biochemical assays for perox idase activity, murine and human progenitor cells were found to have 3 0% and 11% of the peroxidase activity of murine and human unpurified m arrow, respectively. Peroxidase activity was confirmed in purified mur ine and human progenitor populations by flow cytometry using a 2,7-dic hlorofluorescein assay, adapted to measure peroxidase activity. In add ition, two-color flow cytometry of murine whole marrow using phycoeryt hrin-conjugated antibodies to lineage markers confirmed the peroxidase activity of the murine progenitor cell population. A reverse transcri ption-polymerase chain reaction assay was developed for MPO mRNA, whic h was detected in murine progenitor cells. These data show that MPO mR NA is expressed in murine progenitor cells and that both murine and hu man progenitor cells have marked peroxidase activity. These data may h ave relevance for studies of hematopoietic cell differentiation and fo r the examination of mechanisms underlying cell-specific toxicity in b one marrow.