Metabolic and cellular basis of 2-butoxyethanol-induced hemolytic anemia in rats and assessment of human risk in vitro.

Recent work in this laboratory indicated that 2-butoxyethanol (BE) causes acute hemolytic anemia in rats, and activation of BE to butoxyacetic acid (BAA), presumably through the intermediate 2-butoxyacetaldehyde (BAL), is a prerequisite for development of hematotoxicity. In the present studies, the effects of BE and its metabolites, BAL and BAA, on erythrocytes from rats and humans were investigated in vitro. Incubation of BE (up to 10 mM) with blood from male F344 rats caused no hemolysis and resulted in no metabolic alteration of BE. Further, addition of alcohol and aldehyde dehydrogenases, with their co-factors, to the incubation mixture failed to alter BE or its effect. At 20 mM, BE caused significant (P less than or equal to 0.05) hemolysis of rat erythrocytes accompanied by a significant (P less than or equal to 0.05) decrease in hematocrit (HCT). In contrast, incubation of BAL or BAA with rat blood caused time- and concentration-dependent swelling of red blood cells followed by hemolysis; however, BAA was significantly more efficacious than BAL. Addition of aldehyde dehydrogenase and its co-factors significantly (P less than or equal to 0.05) potentiated the effect of BAL on rat erythrocytes. Further in vitro investigation of the cellular mechanisms involved in the hemolytic effect revealed that incubation of rat blood with BAA or BAL caused a time- and concentration-dependent decrease in blood ATP concentration. As observed with the hemolytic effects, the decrease in blood ATP was significantly (P less than or equal to 0.05) greater with BAA than with BAl and was not induced by BE. Further, BAA caused no significant changes in the concentration of reduced glutathione and glucose-6-phosphate dehydrogenase in rat erythrocytes. Assessment of human sensitivity by incubation of human blood with BAA showed minimal swelling or hemolysis of erythrocytes with minimal decline in blood ATP levels at BAA concentrations several-fold higher than required to cause complete hemolysis of rat erythrocytes. In summary, the current studies confirm that the hemolytic effect of BE can be attributed primarily to its metabolite BAA, that hemolysis of rat erythrocytes by BAA or BAL is preceded by swelling and ATP depletion, suggesting that the erythrocyte membrane is the most likely target, and, finally, that human erythrocytes are comparatively insensitive to the hemolytic effects of BAA in vitro.