Enhancement by ethyl alcohol of experimental hepatocarcinogenesis induced by N‐nitrosomorpholine

Abstract

The effects of ethyl alcohol (EtOH) during or after treatment with N-nitrosomorpholine (NNM) on hepatocarcinogenesis, ornithine decarboxylase (ODC) activity and the labeling index of the liver were investigated in male Sprague-Dawley rats. Rats were given drinking water containing NNM for 8 weeks and received i.p. injections of 1 g EtOH/kg body weight every other day during or after treatment with NNM. Preneoplastic and neoplastic lesions staining positively for glutathione-S-transferase, placental type (GST-P), were examined immunohistochemically. At the end of experiment at week 16, administration of EtOH after NNM treatment had no significant effect on the number and size of GST-P-positive hepatic lesions, whereas administration of EtOH during NNM treatment significantly increased the number and percentage area but not the mean area of GST-P-positive hepatic lesions. EtOH caused significant increases in the ODC activity of the liver and in the labeling indices of enzyme-altered lesions and the adjacent hepatocytes after the cessation of EtOH administration but not during EtOH treatment. Our findings indicate that EtOH enhances hepatocarcinogenesis and suggest that this effect may be closely related to the increases in ODC activity and cell proliferation in enzyme-altered lesions and the adjacent liver after EtOH treatment. Int. J. Cancer 71:1045-1048, 1997.r 1997 Wiley-Liss, Inc.Consumption of alcoholic beverages has been linked to an increased risk of hepatocellular carcinoma (HCC) in humans. Case-control studies (Oshima et al., 1984;Tsukuma et al., 1990) of HCC and alcohol consumption have shown a significantly increased risk of HCC in heavy drinkers. Ethanol (EtOH) also has been found to enhance hepatic tumorigenesis (Yamagiwa et al., 1994). However, the mechanism by which alcohol induces cancers in humans is not clear.Epidemiologically, Tsukuma et al. (1993) have reported that the risk of HCC is significantly increased in former heavy drinkers but is small and insignificant in current heavy drinkers. These findings suggest that alcohol at an initiation phase may have an important role in hepatocarcinogenesis. Therefore, to investigate this possibility, in the present work, we examined the effect of EtOH given during or after administration of the carcinogen N-nitrosomorpholine (NNM) on hepatocarcinogenesis in rats. MATERIAL AND METHODS AnimalsNinety inbred Sprague-Dawley rats, initially weighing 150 g, were purchased from Japan SLC (Shizuoka, Japan). Rats were housed in suspended cages with wire mesh bottoms in a room with controlled temperature (21 6 1°C) and humidity (40 6 10%) and a 12:12 light:darkness cycle and given free access to regular chow pellets (Nihon-Nosan, Yokohama, Japan). Experimental designAnimals were randomly divided into 3 groups of 30 rats each and from the beginning of the experiment were given drinking water containing 175 mg/l of NNM (Sigma, St. Louis, MO) for 8 weeks. NNM was dissolved in distilled water at a concentration of 50 g/l and stored in a cool place. The stock solution ...

Chronic ethanol intake promotes double gluthatione S‐transferase/transforming growth factor‐α‐positive hepatocellular lesions in male Wistar rats

“…( 42,43,45 ) One of the mechanisms proposed for the promoting effect of ethanol on rat hepatocarcinogenesis is by enhancement of cell proliferation observed during or after interruption of long‐term alcohol exposure. ( 14,15,44 ) In the present study, the mean rates of cell proliferation were significantly higher in TGF‐α‐positive than in TGF‐α‐negative PNLs. Ethanol feeding at 5% resulted in clear promoting activity as observed by the increased percentage of the liver occupied by PNLs and mean PNL size.…”

“…Some studies demonstrated that ethanol exerts a promoting activity on rat hepatocarcinogenesis. ( 14–16 ) However, few investigations have examined this effect at low ethanol doses and little attention has been given to the differential effects of ethanol on PNL phenotypic diversities. The results of the present study show that chronic feeding of ethanol at a low dose promotes a selective growth of remodeling and persistent PNLs with double GST‐P/TGF‐α markers.…”

“…There are some controversies in rodent liver carcinogenesis assay concerning whether ethanol is a promoting agent ( 14–16 ) or exerts cocarcinogenic effects ( 17,18 ) or neither. ( 19–21 ) The exact mechanism(s) of ethanol‐associated carcinogenesis remains obscure, since this abuse drug per se is not considered a carcinogen in experimental hepatocarcinogenesis studies.…”

“…(12) Also, in fibrotic liver there is an increased expression of TIMPs, which play an important role in the regulation of MMPs activities, including the gelatinases 2 and 9. (11)(12)(13) There are some controversies in rodent liver carcinogenesis assay concerning whether ethanol is a promoting agent (14)(15)(16) or exerts cocarcinogenic effects (17,18) or neither. (19)(20)(21) The exact mechanism(s) of ethanol-associated carcinogenesis remains obscure, since this abuse drug per se is not considered a carcinogen in experimental hepatocarcinogenesis studies.…”