Toxicogenomics of drug-induced hemolytic anemia by analyzing gene expression profiles in the spleen.

Hemolytic anemia is a serious adverse effect of therapeutic drugs that is caused by increased destruction of drug-damaged erythrocytes by macrophages in the spleen and liver. We previously applied a toxicogenomic approach to the toxicity by analyzing microarray data of the liver of rats dosed with two hemolytic agents: phenylhydrazine and phenacetin. In the present study, we analyzed gene expression profiles in the spleen, the primary organ for destruction of damaged erythrocytes, of the same models in order to identify splenic gene expression alterations that could be used to predict the hematotoxicity. Microarray analyses revealed hundreds of genes commonly deregulated under all severe hemolytic conditions, which included genes related to splenic events characteristic of the hematotoxicity, such as proteolysis and iron metabolism. Eleven upregulated genes were selected as biomarker candidates, and their expression changes were validated by quantitative real-time PCR. The transcript levels of most of these genes showed strong correlation with the results of classical toxicological assays (e.g., histopathology and hematology). Furthermore, hierarchical clustering analysis suggested that altered expression patterns of the 11 genes sensitively reflected the erythrocyte damage even under a condition that caused no decrease in erythrocyte counts. Among the selected genes, heme oxygenase 1 was one of the most promising biomarker candidates, the upregulation of which on the protein level was confirmed by immunohistochemistry. These results indicate that altered splenic expression of a subset of genes may allow detection of drug-induced hemolytic anemia, with better sensitivity than that of erythrocyte counts in the blood.