INDUCTION OF CYTOCHROME P4501A1 IN HEMATOPOIETIC STEM-CELLS BY HYDROXYLATED METABOLITES OF BENZENE

The ability of various metabolites of benzene to regulate the expressi on of cytochrome P-450 (CYP)1A1 mRNA in human haemopoietic cells was i nvestigated. CYP1A1 mRNA was quantified using a Northern blot techniqu e and high stringency hybridization with a P-32-labelled cDNA probe. B enz[a]anthracene (BA, 1 or 10 mu M), used as a positive control, induc ed CYP1A1 mRNA in two out of three human leukaemic haemopoietic stem c ell lines (positive: KG-1, U937; negative: HL-60), as well as in long- term bone marrow cultures established from healthy volunteers. In KG-1 and U937 cells, CYP1A1 mRNA induction was studied in the presence of the benzene metabolites, hydroquinone (HQ), p-benzoquinone (BQ), pheno l (PHE) and catechol (CAT). HQ and BQ induced CYP1A1 mRNA when added a t concentrations of 100 nM or more; CAT was active at a concentration of 1 mu M, whereas PHE had almost no effect, even at the highest conce ntration used (1 mu M). Maximum mRNA levels induced by 1 mu M HQ were seen at 6 and 12 hr after addition of inducers, and induction was dete ctable for at least 48 hr. Little, if any, cellular toxicity was seen in clonogenic assays of KG-1 cells at concentrations of maximum induct ion. In conclusion, CYP1A1 mRNA induction was demonstrated in haemopoi etic cells; inducers for CYP1A1 were not only a polycyclic aromatic hy drocarbon (BA), but also, unexpectedly, hydroxylated metabolites of be nzene.