Toxicity profile of benzo[a]pyrene in the male LacZ transgenic mouse (MutaMouse) following oral administration for 5 consecutive days

The toxicity profile of benzo[a]pyrene (BP) was examined in the MutaMouse. The transgenic mouse integrated with lambda gt10 lacZ vectors is used worldwide as an experimental animal in in vivo mutagenesis testing systems. There are few toxicity studies including carcinogenicity in the MutaMouse, and so far only a few carcinogenicity studies of BP accompanied with hematological and plasma biochemical examinations have been conducted even in generic mice. Accordingly, male mice were orally administered BP at doses of 75 and 125 mg/kg/day for 5 consecutive days, and complete autopsy was conducted together with pathological, hematological, and plasma biochemical examinations and measurement of organ weights 41 weeks after the last treatment. Squamous cell papilloma and hyperplasia in the forestomach were induced at incidences of 25 and 50%, respectively and were induced 26 weeks after the final treatment without any significant alterations in t he hematological and plasma biochemical parameters in mice of the 125 mg/kg/day BP-treated satellite group. Fourty-one weeks after the final treatments, 75 and 125 mg/kg/day BP induced squamous cell carcinoma, papilloma, and hyperplasia in the forestomach at incidences of 18 and 18%, 36 and 45%, and 91 and 91%, respectively, and anemia possibly due to continuous hemorrhage from tumors in the forestomach. BP (125 mg/kg/day) also produced malignant lymphoma with an incidence of 18%, accompanied by a marked increase in leukocyte count and decrease in erythrocyte count and by a remarkable decrease in body weights 26 and 39 weeks after the last treatment. Moreover, administration of 75 and 125 mg/kg/day BP induced bronchiolar-alveolar hyperplasia in the lung at incidences of 18 and 9%, respectively. Slight increases were also observed in the weight of the liver and in the levels of urea nitrogen, creatinine, and potassium ion in the plasma biochemical examinations, although no significant pathological alterations were found in the liver and kidney. This study provides new information about BP toxicity including carcinogenicity in the MutaMouse developed for in vivo mutational analysis.

Comparison between in vivo mutagenicity and carcinogenicity in multiple organs by benzo[a]pyrene in the lacZ transgenic mouse (Muta Mouse)

To evaluate whether the in vivo mutagenicity test system using the lacZ transgenic mice (Muta Mouse) may be applied to carcinogenesis studies, both the in vivo mutagenicity and carcinogenicity of benzo[a]pyrene (BP) was tested in mice under the same administration conditions. The eleven organs of the mice on the 14th day after the final oral administration of BP at a dose of 125 mg kg(-1) day(-1) or corn oil for 5 consecutive days were tested for in vivo mutation by the positive-selection method. The data show that the colon had the highest lacZ mutant frequency (37-fold increase over the spontaneous frequency), followed by the ileum > forestomach > bone marrow, spleen > glandular stomach > liver, lung > kidney and heart. No significant mutations were found in the brain. These results may suggest that, in general, the organs with rapidly proliferative tissues have a marked increase in vivo mutant frequencies under the conditions of this experimental design. The forestomach and lymphatic organs including the spleen (malignant lymphoma) were the main target organs for BP carcinogenesis by 5 daily oral doses of 75 and 125 mg kg(-1) day(-1). These results suggest that the mutation results from the transgenic assay with BP reflect the carcinogenicity of BP in the mouse. They also indicate, however, that the magnitude of the in vivo lacZ mutant frequencies induced by BP in different organs did not fully correlate with the target organs for carcinogenicity.