Long-term effect of benzene in C57BL/6N mice

Chemical of current interest--benzene

Benzene is one of the world's major commodity chemicals. It is derived from petroleum and coal and is used both as a solvent and as a starting material in chemical syntheses. The numerous industrial uses of benzene over the last century need not be recounted here, but the most recent addition to the list of uses of benzene is as a component in a mixture of aromatic compounds added to gasoline for the purpose of replacing lead compounds as anti-knock ingredients. The best known and longest recognized toxic effect of benzene is the depression of bone marrow function seen in occupationally exposed individuals. These people have been found to display anemia, leucopenia, and/or thrombocytopenia. When pancytopenia, i.e., the simultaneous depression of all three cell types, occurs and is accompanied by bone marrow necrosis, the syndrome is called aplastic anemia. In addition to observing this decrease in humans and relating it to benzene exposure, it has been possible to establish animal models which mimic the human disease. The result has been considerable scientific investigation into the mechanism of benzene toxicity. Although the association between benzene exposure and aplastic anemia has been recognized and accepted throughout most of this century, it is only recently that leukemia, particularly of the acute myelogenous type, has been related to benzene. The acceptance of benzene as an etiological agent in aplastic anemia in large measure derives from our ability to reproduce the disease in most animals treated with sufficiently high doses of benzene over the necessary time period. Unfortunately, despite extensive efforts in several laboratories, it has not been possible to establish a reproducible, reliable model for the study of benzene-induced leukemia. The recent demonstration that several animals exposed to benzene either by inhalation or in the drinking water during studies by Drs. B. Goldstein and C. Maltoni suggests that such a model may be forthcoming. Nevertheless, at this time it is not clear whether bone marrow damage of the type that leads to aplastic anemia is required for the development of leukemia. Most studies of benzene toxicity have involved dosing animals with benzene either by inhalation or by injection, using high doses to ensure a toxic response. Very few studies have concentrated on the oral route of administration and none have concentrated on administering benzene by mouth at the low doses occasionally detected in drinking water.(ABSTRACT TRUNCATED AT 400 WORDS)

Benzene inhalation produces leukemia in mice

Female C57Bl/6 mice were exposed to 300 ppm benzene 6 hr/day, 5 days/week for 16 weeks and then held for lifetime observation. Sixty-four weeks after commencement of the study, 10 of 90 exposed mice had died as opposed to only 1 of 88 controls. Of the 10 exposed mice that died, 6 had thymic lymphomas, 2 had unspecified lymphomas, 1 was killed when moribund and found leukemia-free, and 1 was undiagnosed due to autolysis and partial cannibalization. The single dead control animal did not have lymphoma or leukemia. These data provide proof of the leukemogenicity of benzene in female C57Bl/6 mice.

Tumors of the mouse hematopoietic system: their diagnosis and interpretation in safety evaluation tests. Report of a study group

A nomenclature for tumors of the mouse hematopoietic system is proposed. This nomenclature, which will be particularly appropriate for use in safety assessment studies, employs basic cytologic terminology, and subclassifications may take into consideration tissue sites and the presence or absence of leukemia. Analysis of tumor incidence in any given study can take into account the consolidation or separation of various tumor types as pathological and biological judgment indicates. The proposed system should be easily understood by pathologists and can be related to other species. Safety assessments of substances that induce tumors of the murine hematopoietic tumors are complicated by difficulty in diagnosis, by the possible involvement of oncogenic viruses, and by other factors such as genetics, immune status, endocrine status, and diet. These various influences are evaluated in respect to interpretation of safety evaluation data.

An evaluation of the associations of leukemia and rubber industry solvent exposures

Excessive leukemia mortality has appeared consistently in epidemiological studies of British and U.S. rubber industry workers. Attempts to identify causative factors have focused on exposure to benzene and other solvents. Interpretations of findings from these studies have often been influenced by expectations of a benzene/nonlymphocytic leukemia association, seen from previous work in other settings. However, data from the rubber industry studies have not been consistent with this expectation, as lymphocytic and nonlymphocytic leukemia have shown similar mortality excesses. Data from a small case-control study of lymphocytic leukemia are presented to illustrate an approach that considers multiple solvent exposures. The associations with lymphocytic leukemia risk observed for a number of solvents, most notably carbon tetrachloride and carbon disulfide, were stronger than those detected for benzene.