Carcinogenesis, Vol 18, 31-36, Copyright © 1997 by Oxford University Press
SY Chiang, JA Swenberg, WH Weisman and TR Skopek
Vinyl chloride (VC), a known human and rodent carcinogen, is metabolically
activated by cytochrome P450 to chloroethylene oxide (CEO), which can
rearrange to chloroacetaldehyde (CAA) or undergo hydrolysis. To further
understand the roles of CEO and CAA in VC mutagenesis, the types and
frequencies of mutations induced at the hypoxanthine (guanine)
phosphoribosyl-transferase (hprt) locus were examined in a human
B-lymphoblastoid line constitutively expressing human cytochrome P450 2E1
(H2E1 cells). VC was toxic and mutagenic to H2E1 cells as a function of
incubation time; exposure to 7.5% VC in air resulted in 75% survival and an
hprt mutant frequency of 42 x 10(-6) after 48 h, compared to 5.7 +/- 2.7 x
10(-6) for unexposed cells. The exposure of H2E1 cells to 0.8 to 15.0% VC
in air produced similar mutant frequencies without a clear dose-response
relationship, suggesting saturation of metabolic activation. Both CEO and
CAA exhibited dose-dependent increases in cell killing and mutant frequency
in H2E1 cells. Treatment with 16 microM CEO for 24 h resulted in 75%
survival and an induced mutant frequency of 23 x 10(-6), while 16 microM
CAA produced 5% survival and an induced mutant frequency of 20 x 10(-6).
Structural alterations at the hprt locus in independent
thioguanine-resistant clones were examined by Southern blot analysis of Pst
I-digested DNA with a full-length human hprt cDNA probe. Ten percent (5/50)
of VC-induced and 18% (7/38) of CEO-induced mutants showed detectable
deletions, compared with 45% (9/20) of CAA-induced mutants. Thus, VC and
CEO displayed similar toxicity/mutation profiles and a similar frequency of
large deletions, whereas CAA displayed greater toxicity and a larger
frequency of deletion mutations. These results suggest that the majority of
mutations induced by VC occur through its metabolite, CEO.
ARTICLES
Mutagenicity of vinyl chloride and its reactive metabolites, chloroethylene oxide and chloroacetaldehyde, in a metabolically competent human B-lymphoblastoid line
Department of Environmental Sciences and Engineering, University of North Carolina, Chapel Hill 27599, USA.
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