Evidence for the disruption of the bone marrow microenvironment by combined exposures to inhaled benzene and ingested ethanol.

Studies have been performed to investigate the effects of combined in vivo exposures to inhaled benzene and ingested ethanol on the earliest known murine erythropoietic precursor cells, the Burst Forming Unit--Erythroid (BFU-E) and the Colony Forming Unit--Erythroid (CFU-E). Previously we had determined that murine erythropoietic cell populations were particularly susceptible to combined benzene + ethanol treatments. The most striking example of erythropoietic disruption was the transient appearance of large numbers of nucleated red cells (normoblasts) in the circulating blood. In the present studies, male C57Bl/6 mice were exposed to 300 ppm benzene via inhalation for 6 h/d x 5 d/wk x 9 wks. Groups of mice were also exposed to 5% ethanol in the drinking water 4 d/wk x 9 wks. Appropriate controls were also maintained. The hematological assays were performed after 1, 4, and 9 weeks of exposure. After 4 weeks of exposure large numbers of normoblasts appeared in the circulating blood of mice exposed to benzene + ethanol. However, there were no corresponding increases in the numbers of the earliest erythroid progenitor cells in the bone marrow. There were, however, marked increases in the numbers of these cells in the spleen. Previous work in this laboratory had confirmed that the marrow was the source of circulating normoblasts among animals exposed to benzene + ethanol. We conclude, therefore, that circulating normoblasts appear in the peripheral blood because of changes in the bone marrow microenvironment rather than as a consequence of increased erythropoietic proliferation in the marrow.