CHROMOSOMAL LOSS AND BREAKAGE IN MOUSE BONE-MARROW AND SPLEEN-CELLS EXPOSED TO BENZENE IN-VIVO

Benzene is a widely recognized human and animal carcinogen. In spite o f considerable research, relatively little is known about the genotoxi c events that accompany benzene exposure in vivo. To gain insights int o the mechanisms underlying the genotoxic effects of benzene, we have charac terized the origin of the micronuclei that are formed in bone m arrow erythrocytes and splenic lymphocytes of benzene-treated mice usi ng two molecular cytogenetic approaches: (a) fluorescence in situ hybr idization with a centromeric DNA probe; and (b) staining with the calc inosis-Raynaud's phenomenon-esophageal dismobility-sclerodactyly-telan giectasia syndrome of scleroderma (CREST) antibody, an antibody recogn izing a centromeric protein. Following the p.o. administration of benz ene (220 or 440 mg/kg) to male CD-1 mice, a significant increase in mi cronuclei was observed in the bone marrow erythrocytes. In situ hybrid ization with a centromeric DNA probe and immunofluorescent staining wi th the CREST antibody indicated that the micronuclei in bone marrow er ythrocytes were formed from both chromosome loss and breakage. The maj ority of the micronuclei originated from chromosome breakage. A dose-r elated increase in micronucleated cells was also observed in splenocyt e cultures established from these benzene-treated animals. In contrast to the bone marrow erythrocyte results, the majority of benzene-induc ed micronuclei in the cytokinesis-blocked splenocytes labeled with the CREST antibody indicating that these micronuclei were the result of w hole chromosome loss. These data demonstrate that both aneuploidy and chromosomal breakage are early genotoxic events induced by benzene or its metabolites in vivo and also indicate that the nature of the chrom osomal alterations may vary depending on the target organ or cell type .