title: Induction of preneoplastic rat liver lesions with an attenuated p53 response by low doses of diethylnitrosamine.
abstract: Previous reports have documented an attenuated p53 response to DNA-damage in preneoplastic enzyme-altered foci (EAF). Data suggest that this alteration is an adaptation to genotoxic stress induced by carcinogens. Here, we have studied whether the altered p53 response in EAF can be related to acutely apoptotic or cytotoxic doses of the carcinogen diethylnitrosamine (DEN). Eight groups of rats received cumulative doses of 0.25, 0.5, 1.0 and 2.0 mmol DEN/kg, administered weekly for either 10 or 20 weeks. A ninth group received 3.0 mmol/kg for 10 weeks, which gave a supralinear EAF response. Twenty-four hours before sacrifice, all rats were given a challenge dose of DEN in order to induce a p53 response in hepatocytes. The numbers of p53-positive hepatocytes in EAF and in surrounding tissue were analyzed. Unexpectedly, all cumulative doses gave rise to p53-negative EAF and 20-week treatment gave larger EAF with fewer p53-positive hepatocytes than 10-week treatment. It was also observed that at the lowest doses, most EAF developed in midzonal areas. Similar results were obtained with aflatoxin B1. Single high doses of DEN induced p53 accumulation and apoptosis within 24 h, whereas lower doses did not. It is concluded that EAF with an attenuated p53 response can be induced by low doses of genotoxic compounds, not giving rise to acute apoptosis or necrosis. Instead, it is suggested that time is an important determinant for its development at low doses and that a delayed type of apoptosis might be important.
authors.affiliation: Institute of Environmental Medicine, Karolinska Institutet, Box 210, S-171 77 Stockholm, Sweden.
authors.forename: Ilona
authors.initials: I
authors.lastname: Silins
authors.forename: Ulla
authors.initials: U
authors.lastname: Stenius
authors.forename: Johan
authors.initials: J
authors.lastname: Högberg
mesh_terms: D000818:Animals; D004052:Diethylnitrosamine / Q000633:toxicity*; D004305:Dose-Response Relationship, Drug; D005260:Female; D051549:Glutathione S-Transferase pi; D005982:Glutathione Transferase / Q000096:biosynthesis*; D007150:Immunohistochemistry; D020287:In Situ Nick-End Labeling; D007527:Isoenzymes / Q000096:biosynthesis*; D008099:Liver / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism / Q000473:pathology; D008114:Liver Neoplasms, Experimental / Q000139:chemically induced / Q000201:enzymology* / Q000378:metabolism / Q000473:pathology; D009687:Nuclear Proteins / Q000096:biosynthesis; D011230:Precancerous Conditions / Q000139:chemically induced / Q000201:enzymology* / Q000378:metabolism / Q000473:pathology; D018809:Proliferating Cell Nuclear Antigen / Q000096:biosynthesis; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis; D051736:Proto-Oncogene Proteins c-mdm2; D051381:Rats; D017207:Rats, Sprague-Dawley; D016159:Tumor Suppressor Protein p53 / Q000096:biosynthesis*
chemical_list: D007527:Isoenzymes; D009687:Nuclear Proteins; D018809:Proliferating Cell Nuclear Antigen; D011518:Proto-Oncogene Proteins; D016159:Tumor Suppressor Protein p53; D004052:Diethylnitrosamine; C497208:Mdm2 protein, rat; D051736:Proto-Oncogene Proteins c-mdm2; D051549:Glutathione S-Transferase pi; D005982:Glutathione Transferase; C496558:Gstp1 protein, rat