The correlation between DNA adducts and chromosomal aberrations in the target organ of benzidine exposed, partially-hepatectomized mice.

An experimental system was developed to test the association between benzidine--DNA adduct levels and chromosome aberrations in the target organ, the liver, of mice. A 2/3 partial hepatectomy was performed (0 h), then the animals were treated with benzidine (0, 7.8, 19.5, 38.2 or 97.8 mg/kg, i.p.) and an agar-coated 50 mg 5-bromodeoxyuridine tablet was implanted subcutaneously (58 h). Colcemid was given at 4 mg/kg i.p. (70 h), and the animals were sacrificed 2 h later. The liver from each animal was divided, with portions allocated for cytogenetics and DNA adduct analysis. DNA adducts were analyzed with the 32P-postlabeling technique. DNA adduct and chromosomal aberration data were available on a total of 43 animals. Benzidine was shown to be a potent clastogen in liver, the target organ, as opposed to its reported weak activity in the bone marrow. A linear dose response was demonstrated for benzidine--DNA adducts found in the liver. The correlation between adduct levels and aberrations in individual animals was 0.43 (P less than 0.05). However, most of the residual variance was due to four outlying cases. When these cases were removed from the data set and the analysis repeated, the linear correlation coefficient increased to 0.74. When the data were analyzed by dose groups, the correlation was 0.91. These data support the hypothesis that carcinogen-DNA adducts are responsible for the induction of chromosomal aberrations, and perhaps other genotoxic events, including neoplasia.