Differential Effects of Partial Hepatectomy and Carbon Tetrachloride Administration on Induction of Liver Cell Foci in a Model for Detection of Initiation Activity

Abstract

Differential effects of partial hepatectomy (PH) and carbon tetrachloride (CCl 4 ) administration on induction of glutathione S-transferase placental form (GST-P)-positive foci were investigated in a model for detection of initiation activity. Firstly, we surveyed cell proliferation kinetics and fluctuation in cytochrome P450 (CYP) mRNA levels by means of relative-quantitative real-time reverse transcriptase-polymerase chain reaction (RT-PCR) and CYP 2E1 apoprotein amount by immunoblotting (experiment I) after PH or CCl 4 administration. Next, to assess the interrelationships among cell proliferation, fluctuation of CYPs after PH or CCl 4 administration and induction of liver cell foci, the non-hepatocarcinogen, 1,2-dimethylhydrazine (DMH) was administered to 7-week-old male F344 rats and initiated populations were selected using the resistant hepatocyte model (experiment II). In experiment I, the values of all CYP isozyme mRNAs after PH or CCl 4 administration were drastically decreased at the 12-h time point. From 72 h, mRNAs for all CYP isozymes began increasing, with complete recovery after 7 days. The CYP 2E1 apoprotein content in the PH group fluctuated weakly, whereas in the CCl 4 group it had decreased rapidly after 12 h and was still low at the 48 h point. In experiment II, induction of GST-P-positive foci was related to cell kinetics in the PH group, with about a 6-h time lag between time for carcinogen administration giving greatest induction of GST-P-positive foci and peaks in bromodeoxyuridine (BrdU) labeling, presumably due to the necessity for bioactivation of DMH. With CCl 4 administration, induction of foci appeared dependent on the recovery of CYP 2E1. In conclusion, PH was able to induce cell proliferation with maintenance of CYP 2E1, therefore being advantageous for induction of liver cell foci in models to detect initiation activity.

Detection of Initiation Activity of 1,2-Dimethylhydrazine in in vivo Medium-Term Liver Initiation Assay Ssytem using 4-Week-Old Rats without Hepatocellular Proliferative Stimuli during the Test Chemical Treatment Period

“…Chemical hepatectomy (CH) and the fasting/refeeding method are very simple as compared with PH, but these methods also entail certain problems. Hepatotoxicants such as carbon tetrachloride (CCl 4 ), allyl alcohol, and d-galactosamine have been used for CH; however, although they induced hepatocyte proliferation, the induction of GST-Ppositive foci in the medium-term liver initiation assay model with these cell proliferation stimuli was lower than that with PH in previous studies [27,33,[39][40][41]. The reason is possibly that the induction of hepatocyte proliferation after the administration of these hepatotoxicants was lower than that after PH; moreover, when hepatocyte proliferation activity was increased, the hepatic metabolic enzymes causing metabolic activation of procarcinogen were markedly decreased by hepatotoxicity of these hepatotoxicants.…”

“…Human exposure to environmental carcinogens is usually limited to low concentrations and human are generally exposed to such carcinogens over a long-term period [1,7,49]; therefore, multiple low-dose administration would be expected to be superior to single high-dose administration for extrapolation to carcinogenesis in humans. Generally, previous assay models using a cell proliferation stimulus tested only single or multiple doses over 1-day administration of test chemicals because the induction of hepatocyte proliferation could be maintained only for approximately 1 day [2,39]. In the current study, hepatocyte proliferation activity in 4-weekold rats was significantly higher than that in 8-week-old rats and continued at high levels until 4.5 weeks of age in experiment I, and the induction of GST-P-positive foci by 4-day divided doses of DMH was approximately equal to that with the same total single dose of DMH in experiment II.…”

The Effects of Allyl Alcohol-induced Cell Proliferation for Detection of Initiation Activities of Chemicals in Rat Liver.

“…PH strongly induces cell proliferation in rat liver, however, surgical hepatectomy is intricate, especially when large quantities of rats are hepatectomized. Similarly, carbon tetrachloride (CCl 4 ) has also been used for the induction of cell proliferation 7,13,16 . CCl 4 induced hepatic necrosis in the centrilobular area where drug-metabolizing enzymes are found such as cytochrome P450 (CYP), which cause a remarkable decrease, and therefore the bioactivation of carcinogens may be affected 7,17,18 .…”

“…Many different methods of analyses such as the Ito method have already been developed 3,4 , and many chemicals have already been examined by this Ito method 1,5,6 . We have developed an in vivo five-weeks initiation assay model in order to detect the initiation activities of chemicals 7,8 , and 26 chemicals have been evaluated so far 9 . Regardless of the target organ, mutagenic carcinogens are detected by the induction of glutathione S-transferase placental form (GST-P) positive foci in rat liver 9 .…”

“…Furthermore, most chemical carcinogens are procarcinogens that require conversion to ultimate carcinogens within the body 14,15 , thus the bioactivation of chemicals is also important. For induction of cell proliferation, two-third partial hepatectomy (PH) has been utilized in an in vivo five-weeks initiation assay model [7][8][9]12 . PH strongly induces cell proliferation in rat liver, however, surgical hepatectomy is intricate, especially when large quantities of rats are hepatectomized.…”