Molecular analysis of hprt mutant lymphocytes from 1, 3-butadiene-exposed workers

1,3-Butadiene (BD) has been shown to be a potent animal carcinogen and a probable human carcinogen, yet the molecular mechanisms of BD genotoxicity and carcinogenicity still are not fully understood. Our hypothesis is that metabolites of BD induce specific structural changes in the human hprt gene like those observed in vitro in TK6 cells and in vivo in the mouse. Characteristic mutations in BD-exposed subjects can be identified and used as biomarkers for monitoring genotoxic effects associated with BD exposure. Molecular analysis of hprt mutant lymphocytes from BD-exposed workers and unexposed control subjects was carried out to identify changes in the structure of the hprt gene. A multiplex polymerase chain reaction (PCR) assay was used to detect exon deletions in 360 hprt mutant clones. We determined that exon deletions were significantly more frequent (P < 0.05) in BD-exposed workers (17.5%) than in control subjects (9.7%). Sequence analysis of hprt cDNA from 175 independent mutants indicated that the distribution of the types of mutations was different between the workers and the unexposed control subjects. There was a significant increase in -1 frameshift mutations in BD-exposed workers, predominantly in repeated DNA sequences, and single-base substitutions were decreased to 66% in the workers compared to 83% in the control subjects (P < 0.05). In addition to the spectral changes, hprt clonal assays revealed an elevation in mutant frequency in the lymphocytes of workers (N = 10) when compared with that in unexposed control subjects (N = 11; P < 0. 05). There also was a twofold increase of A:T --> T:A transversions in BD-exposed workers (16% in BD-exposed workers compared to 8% in controls, P = 0.25). Some of the BD-associated changes in mutational spectra observed in our study have the potential for application in monitoring genotoxic effects related to butadiene exposure.