Comparison of the mutations at Hprt exon 3 of T-lymphocytes from B6C3F1 mice and F344 rats exposed by inhalation to 1,3-butadiene or the racemic mixture of 1,2 : 3,4-diepoxybutane

Experiments were conducted to define the spectra of mutations occurring in Hprt exon 3 of T-cells isolated from spleens of female B6C3F1 mice and F344 rats exposed by inhalation to 1,3-butadiene (BD) or its reactive metabolit e, (+/-)-diepoxybutane (DEB). Hprt mutant frequencies (Mfs) in BD-exposed ( 1250 ppm for 2 weeks or 625 ppm for 4 weeks; 6 h/day, 5 days/week) and DEB- exposed (2 or 4 ppm for 4 weeks or 5 ppm for 6 weeks; 6 h/day, 5 days/week) mice and rats were significantly increased over concurrent control values. Mutant T-cell colonies from control and treated animals were screened for mutations in Hprt exon 3 using PCR amplification of genomic DNA and denatur ing gradient gel electrophoresis, followed by sequence analysis. Exon 3 mut ations were found at the following frequencies: 20/394 (5%) in control mice , 56/712 (8%) in BD-exposed mice, 59/1178 (5%) in BD-exposed rats, 66/642 ( 10%) in DEB-exposed mice, and 51/732 (7%) in DEB-exposed rats. Mutations in exposed animals included base substitutions, small deletions (1 to 74 bp), and small insertions (1 to 8 bp), with base substitutions predominating. A mong the types of base substitutions observed in mice, the proportions of G . C --> A . T transitions (p = 0.035, Fisher's Exact Test) and G . C --> C . G transversions (p = 0.05) were significantly different in control vs. B D-exposed animals. Given the small number of exon 3 mutants analyzed, there was a high degree of overlap in the mutational spectra between BD-exposed mice and rats, between BD- and DEB-exposed mice, and between BD- and DEB-ex posed rats in terms of the sites with base substitutions, the mutations fou nd at those mutated sites, the relative occurrence of the most frequently o bserved base substitutions, and the occurrence of a consistent strand bias for the most frequently observed base substitutions. The spectra data sugge st that adduction of both G . C and A . T bps is important in the induction of in vivo mutations by BD metabolites in exposed mice and rats. (C) 2000 Elsevier Science B.V. All rights reserved.