Relationship between hepatotoxicity and induction of replicative DNA synthesis following single or multiple doses of carbon tetrachloride

The in vivo-in vitro DNA repair and DNA replication assay in mouse hepatocytes has promise as a short-term test for detecting potential mouse liver carcinogens. In addition, this assay may provide information on the mode of action of known hepatic carcinogens. The induction of DNA repair is clearly a response to hepatic DNA damage. However, it is unclear whether induction of replicative DNA synthesis (S phase) represents regenerative hyperplasia in response to hepatotoxicity or is a result of direct mitogenic stimulation of the hepatocytes by the test compound. The objective of the present study was to examine the relationship between hepatotoxicity, which was assessed by measuring serum concentrations of glutamic-oxalacetic transaminase (SGOT), glutamic-pyruvic transaminase (SGPT), alkaline phosphatase (AP), and gammaglutamyl transferase (GGT), and induction of S phase following either single or multiple doses of the model mouse hepatocarcinogen carbon tetrachloride (CCl4). Under the experimental conditions in this study, CCl4 elevated SGPT and SGOT but did not affect serum concentrations of AP or GGT. CCl4 did not induce DNA repair. An increase in the percentage of hepatocytes in S phase followed the appearance of elevated SGOT and SGPT in all single-dose studies. The results from the multiple-dose studies showed a similar relationship except that with 20 mg/kg X d the concentrations of SGOT and SGPT decayed to control values after 14 d of dosing whereas the percentage of hepatocytes in S phase remained markedly elevated (greater than 10 X control). The daily dose of CCl4 that gave a no-observed-effect level for induction of S phase was lower with multiple administrations than it was following a single exposure. A single administration of CCl4 at 25 mg/kg did not increase S phase, SGOT, or SGPT, but if 20 mg/kg X d was given for 7 d the number of hepatocytes in S phase and the concentrations of SGOT and SGPT increased more than 10-fold. These data support the hypothesis that induction of replicative DNA synthesis in the mouse liver following CCl4 administration is related to hepatotoxicity. In single-dose studies elevation in S phase was always associated with elevation of SGOT and SGPT. However, in the multidose studies, SGOT and SGPT declined after 14 d of administering 20 mg/kg X d while S phase remained elevated.(ABSTRACT TRUNCATED AT 400 WORDS)