Analysis of DNA strand breaks induced in rodent liver in vivo, hepatocytes in primary culture, and a human cell line by chlorinated acetic acids and chlorinated acetaldehydes

Abstract

An alkaline unwinding assay was used to quantitate the induction of DNA strand breaks (DNA SB) in the livers of rats and mice treated in vivo, in rodent hepatocytes in primary culture, and in CCRF-CEM cells, a human lymphoblastic leukemia cell line, following treatment with tri- (TCA), di- (DCA), and mono- (MCA) chloroacetic acid and their corresponding aldehydes, tri- (chloral hydrate, CH), di- (DCAA) and mono- (CAA) chloroacetaldehyde. None of the chloroacetic acids induced DNA SB in the livers of rats at 4 hr following a single administration of 1-10 mmole/kg. TCA (10 mmole/kg) and DCA (5 and 10 mmole/kg) did produce a small amount of strand breakage in mice (7% at 4 hr) but not at 1 hr. N-nitrosodiethylamine (DENA), an established alkylating agent and a rodent hepatocarcinogen, produced DNA SB in the livers of both species. TCA, DCA, and MCA also failed to induce DNA strand breaks in splenocytes and epithelial cells derived from the stomach and duodenum of mice treated in vivo. None of the three chloroacetaldehydes induced DNA SB in either mouse or rat liver. The continuous exposure of mice to 5 g/L DCA in the drinking water for 7 and 14 days did not induce appreciable hepatic DNA SB (< 10% at 14 days), although peroxisome proliferation, as evidenced by an increased cyanide-insensitive palmitoyl CoA oxidase (PCO) activity, was stimulated to 490% (7 days) and 652% (14 days) of control. Under this protocol, DENA (0.1 g/L) produced DNA damage after both 7 days (73% of control) and 14 days (57% of control). Similarly, long-term exposure of rats (30 weeks) to 2 g/L DCA in the drinking water, a level that increased PCO activity to 364% of the control value, exhibited no DNA damage. Both the chloroacetic acids and the chloroacetaldehydes were ineffective in inducing DNA SB in cultured rat and mouse hepatocytes at concentrations below those that yielded cytotoxicity. The chloroacetic acids were also ineffective in the CCRF-CEM cells. However, two of the chloroaldehydes, DCAA and CAA, did induce DNA SB in the CCRF-CEM cells at concentrations that did not decrease the cell viability after 2 hr of treatment. Prior incubation of DCAA and CAA with a rat S9 liver homogenate eliminated much of the DNA damaging activity. These studies provide further evidence that the chloroacetic acids lack genotoxic activity not only in rodent liver, a tissue in that they induce tumors, but in a variety of other roden tissues and cultured cell types.(ABSTRACT TRUNCATED AT 400 WORDS)

Mutagenicity of trichloroethylene and its metabolites: implications for the risk assessment of trichloroethylene.

“…TCA was weakly positive in the mouse lymphoma assay. However it was one of the very least potent mutagens ( Figure 5) identified in the assay (31) These results with the neutralized TCA support the observation that TCA is nonclastogenic (63) and the negative results obtained by other researchers (64,65). It is therefore unlikely that TCA would contribute to tumor formation through a mutational mechanism.…”

Mode of action of liver tumor induction by trichloroethylene and its metabolites, trichloroacetate and dichloroacetate.

“…DCA was reported to induce SSBs in hepatic DNA when administered by gavage to both mice and rats (28,107). Subsequent investigators were unable to repeat these results (92,109 (47). Consequently, it is unlikely that these two effects are produced by the same mechanism.…”

A 2-year dose-response study of lesion sequences during hepatocellular carcinogenesis in the male B6C3F(1) mouse given the drinking water chemical dichloroacetic acid.

“…To address these questions, histopathologic analysis was conducted for livers and hepatic lesions arising in B6C3F 1 male mice receiving DCA doses as low as 0.05 g/L for 100 weeks, and DCA at 0.5, 1.0, 2.0, and 3.5 g/L for between 26 and 100 weeks (DeAngelo et al 1999). Nongenotoxic versus potential genotoxic effects of DCA can be separated based on low dose (0.05-1.0 g/L) or low concentrations, where genotoxicity has not been demonstrated, versus high dose (2-3.5 g/L) or high concentrations, where gene mutations and clastogenesis has been observed in several test systems (Chang et al 1992;DeMarini et al 1994;Ferreia-Gonzalez et al 1995;Fuscoe et al 1995;Harrington-Brock et al 1998;Leavitt et al 1997) (Table 8). This analysis suggested a model for DCA-induced carcinogenesis, involving three lesion sequences, that lends itself to testing by mathematical means (Rabinowitz et al 2000(Rabinowitz et al , 2001.…”

“…At the highest concentrations tested, 3.5-5 g/L DCA, there were no differences between strains or sexes in the CA multiplicity respective of the spontaneous tumor background rate (DeAngelo 2000b;DeAngelo et al , 1999. Although high concentrations (> 2 g/L) of DCA induced gene mutations and chromosomal damage (clastogenesis) in several in vivo and in vitro test systems (DeMarini et al 1994;Fuscoe et al 1995;Harrington-Brock et al 1998;Leavitt et al 1997), the role of genotoxicity in the DCA-induced carcinogenic process in vivo has not been clearly defined (Chang et al 1992;Fox et al 1996;Giller et al 1997;Kopfler et al 1985).…”