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PubMed1993

p53 mutations in hepatocellular carcinomas induced by a choline-devoid diet in male Fischer 344 rats.

Analyses were performed on livers and hepatocellular carcinomas from male Fischer 344 rats fed a choline-devoid diet, to assess whether they carried alterations of the p53 tumor suppressor gene. The analyses consisted of immunoperoxidase staining of tissue sections with monoclonal antibodies to p53, Western blotting and cDNA sequencing. Immunostaining revealed the presence of mutant p53 proteins in 22/27 tumors analyzed and immunoblotting in 18/20. Immunochemical evidence was obtained that occurrence of the mutations precedes tumor development. cDNA sequencing was performed on 11 hepatocellular carcinomas that expressed mutant p53 gene proteins. Seven were found to contain point mutations within the 120-290 codon region of the gene, and one a microdeletion in the same region. No mutational hot spot was observed. It is concluded that mutations within the p53 gene, along with a c-myc gene amplification previously detected in these tumors, most likely contribute to the neoplastic transformation of liver cells in this nutritional model of hepatocarcinogenesis. The results are discussed also in view of recent literature on the presence of p53 mutations in human hepatocellular carcinomas.

Animals↗
PubMed1981

Autoradiography of "oval cells" appearing rapidly in the livers of rats fed N-2-fluorenylacetamide in a choline devoid diet.

Autoradiographic analysis of liver sections from rats fed the hepatocarcinogen N-2-fluorenylacetamide (FAA) in a choline devoid (CD) diet suggests that proliferating small "oval" cells arise from a few small portally-situated cells, and spread rapidly across the entire liver lobule. Small cells with detectable grains are first located where liver plates meet the portal areas. This cell type gradually increases in number over a 10-12 day period, then proliferates rapidly. After 28 days, microscopic nodules consisting of heavily labeled large eosinophilic cells appear, whereas residual hepatocytes are not labeled. Combined immunofluorescent and autoradiographic labeling studies reveal that many of the small cells contain AFP; approximately half of the alpha-fetoprotein-containing cells are labeled with [3H]thymidine (dT). Feeding CD-FAA diets to rats with hepatocytes prelabeled with [3H]dT after 70% hepatectomy 7 weeks earlier provides data which suggest that small "oval" cells do not arise from prelabeled hepatocytes but, instead, infiltrate the prelabeled hepatocytes during the diet induced proliferative phase. We conclude that "oval" cells arise from a small number of portal cells, not from hepatocytes. Exact identification of the oval cell precursor is not possible, but it could be a "stem" cell. Although hepatocyte-like properties are found in small cells (e.g., albumin staining), there is no evidence that they differentiate into normally functioning hepatocytes.

2-Acetylaminofluorene↗
PubMed1986

Effects of ethinyl estradiol and tamoxifen on liver DNA turnover and new synthesis and appearance of gamma glutamyl transpeptidase-positive foci in female rats.

We investigated possible mechanisms associated with promotion of hepatocarcinogenesis by the synthetic estrogens mestranol (M) and ethinyl estradiol (EE). Our first objective was to determine whether chronic EE treatment was associated with hepatotoxicity accompanied by regenerative hyperplasia. Female Sprague-Dawley (SD) rats were partially hepatectomized and their liver DNA prelabeled with [3H]thymidine. Two weeks later the rats were treated with EE at three doses or M (using timed-release tablets implanted s.c.) or with 0.05% phenobarbital (PB) in the diet. The rats were killed 6 weeks later and the amount of [3H]thymidine remaining in liver DNA determined. The results showed that none of the promoters caused hepatotoxicity as detected by the loss of prelabeled DNA. EE but not M or PB caused a dramatic dose-dependent enlargement of the pituitary. Subsequent experiments were carried out to define the dose-time response of liver DNA synthesis to treatment with EE, M and PB. Female SD rats were treated with these agents and [3H]-thymidine incorporation into DNA was determined at various times thereafter. The results showed that EE at 2.5 micrograms/day and PB (0.05%) caused a rapid increase in liver DNA synthesis which peaked between 24 and 72 h and remained elevated for at least the next 7 days. Dose-response experiments with EE- and M-treated rats demonstrated that 24 h after beginning treatment, significant increases in liver DNA synthesis could be detected at an EE dose as low as 0.1 microgram/day; DNA synthesis was also significantly increased by M. The anti-estrogen tamoxifen (T), did not cause increased liver DNA synthesis. However, T at 15 micrograms/day did inhibit the induction of DNA synthesis caused by EE and M at 2.5 micrograms/day but not by PB (0.05%). The effect of T on promotion by EE of the appearance of gamma glutamyl transpeptidase (GGT)-positive foci was determined. Female SD rats were initiated with a single i.p. dose of diethylnitrosamine at 20 mg/kg given 24 h after partial hepatectomy. One week later the rats were treated with EE (5 micrograms/day), T (15 or 50 micrograms/day) or EE plus T at both doses using timed-release tablets. The rats were killed after 4 months and the incidence, number and size of the GGT foci determined. The results revealed that, as expected, EE enhanced the appearance of GGT foci. Unexpectedly, T alone at both doses also enhanced the appearance of the foci.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1987

32P-postlabeling analysis of liver DNA adducts in rats chronically fed a choline-devoid diet.

Liver DNA, obtained at various time intervals from rats chronically fed a choline-devoid diet, was analysed for the presence of aromatic or alkyl adducts by the 32P-postlabeling assay. Alkyl adducts were not detected. Aromatic DNA adduct lesions were revealed, but only at levels (1 adduct per 0.5-3 X 10(9) nucleotides) which are at the limits of the extremely high sensitivity of the method used, levels which remained constant throughout the period of feeding. Thus, contamination of the total environment of the animals with chemical carcinogens does not appear to be responsible for the genesis of the hepatocellular carcinomas that develop in rats chronically fed a choline-devoid diet. The diet, therefore, either acts as a complete carcinogen, or promotes the evolution to cancer of endogenous, 'spontaneously' initiated liver cells.

Animals↗
PubMed1987

Liver cell turnover in rats fed a choline-devoid diet.

Liver DNA was labeled in a group of weanling Fischer-344 male rats by placing mini-osmotic pumps, loaded with [methyl-3H]thymidine, under the dorsal skin for 14 days. The animals were then placed on either a choline-supplemented or a choline-devoid diet, and subgroups on each diet were killed after 1, 2, 4, 8 and 16 weeks. Liver DNA total and specific radioactivities were determined in all rats. The results were used to estimate the half-life (t1/2) of liver cells, and the fractional rates of liver cell death (Kd) and proliferation (Kp). In rats fed the control choline-supplemented diet, liver cells were estimated to die at an overall Kd of 0.16% per day, and to have a t1/2 of 439.5 days; Kp was higher in younger than in older rats. In rats fed the choline-devoid diet, liver cells diet at a Kd ranging from 4.82 down to 0.93% per day, as the length of the feeding period increased; corresponding t1/2S were 14.3 and 74.6 days. In these rats, Kp was more than sufficient to compensate for cell loss. The results show that liver-cell death represents a major consequence of feeding a choline-devoid diet to rats, and that the necrogenic action of the diet is a major factor responsible for the highly increased turnover of liver cells present in these animals. However, evidence was obtained that the diet has also a primary mitogenic action, beyond those related to replacement of dead cells, and to cell accretion due to normal growth of the animals and the liver.

Animals↗
PubMed1988

Liver cell proliferation and incidence of hepatocellular carcinomas in rats fed consecutively a choline-devoid and a choline-supplemented diet.

A group-set of male Fischer 344 rats was kept on a choline-devoid (CD) diet for 3, 6, 9, 12 or 16 months. A second set was fed the same diet for 3, 6 and 9 months, followed by a control, choline-supplemented diet for 3 months. A third set was fed the CD diet for 0, 3, 6, 9 and 12 months and the control diet for the duration (16 months) of the experiment. [3H]Thymidine was injected into some of the animals to assess the extent of liver cell proliferation. In the latter animals, liver triacylglycerols were also determined as an index of the hepatonecrogenic action of a CD diet. Foci of enzyme-altered hepatocytes were detected histochemically and the presence of tumors was established histologically. Cell proliferation and triacylglycerols were both high after 3 months and declined steadily as the length of CD diet feeding increased. Upon subsequent feeding with the control diet, triacylglycerols promptly cleared from the liver, while cell proliferation remained at reduced but still relatively high levels for at least 3 months. Increasing but small numbers of foci of enzyme-altered hepatocytes were detected in some of the rats under experimentation for 6 months or longer. The incidence of hepatocellular carcinomas was 13, 27, 33 and 73% respectively in rats fed the CD diet for 3, 6, 9 or 12 months and the control diet for the duration of the experiment. On the other hand, only 26% of the rats fed exclusively the CD diet for 16 months developed carcinomas. The results were taken as evidence that: (i) liver cell proliferation persists beyond discontinuation of a CD diet; (ii) the liver contains initiated cells--capable of full evolution to cancer even in the absence of active promotion--after a relatively short 3-month exposure to a CD diet; and (iii) occurrence of a late event(s) is critical for the genesis of the tumors. Whether a CD diet is a complete carcinogen able to initiate de novo liver cells or acts merely as a promoter of the evolution of endogenous initiated cells is briefly discussed.

Animals↗
PubMed1995

In vivo methylation capacity is not impaired in healthy men during short-term dietary folate and methyl group restriction.

Ten healthy adult men were fed a diet low in folate and exogenous methyl groups to study the effects on in vivo methylation capability. The men were housed in a metabolic unit for the entire 108 d of the study. After a 9-d baseline period (Period 1), the men were fed a soy-product-amino acid defined diet for 45 d, which provided 25 micrograms/d of folate for 30 d (Period 2) and, with a folate supplement, 99 micrograms/d for 15 d (Period 3). During Period 2 and Period 3, the low methionine and choline diet was supplemented with methionine for half the subjects to vary the dietary methyl group intake. The periods were then repeated over the next 54 d (Periods 4-6), with a crossover of methionine intakes in Period 5 and Period 6. A 1-g oral dose of nicotinamide was given at the end of each period and methylated urine metabolites determined. Other measures related to in vivo methylation capability included urine creatinine, and plasma and urine carnitine. Even with moderate folate depletion, none of these measures was decreased by low methionine and choline intakes. Plasma methionine concentrations were unchanged throughout. Limiting exogenous methyl group intake by restricting dietary methionine and choline did not impair in vivo methylation capabilities for the variables tested, even at low folate intake.

Administration, Oral↗
PubMed1985

Methylation of the alphafetoprotein gene in cell populations isolated from rat livers during carcinogenesis.

We examined the methylation pattern and organization of the AFP gene in whole livers and in isolated cell populations purified from livers of rats fed a carcinogenic diet which interferes with DNA methylation. Using restriction endonuclease digestion, we find no differences in methylation pattern and overall organization of the AFP gene in oval cells (AFP-producers) and hepatocytes (non-producers) isolated at the early stages of carcinogenesis. Our studies indicate that in cell populations which produce AFP as well as in cells which are not active in AFP synthesis, the majority of the CCGG sites of the AFP gene are extensively methylated. In addition, we describe the existence of polymorphism in the AFP and albumin genes of Sprague-Dawley rats.

Albumins↗