Liver regeneration and alpha-fetoprotein messenger RNA expression in the retrorsine model for hepatocyte transplantation.

Recently, we described a new model for hepatocyte transplantation with nearly total replacement of the liver by exogenous hepatocytes (E. Laconi et al., Am. J. Pathol., 153: 319-329, 1998). The model is based on the mitoinhibitory effect of the pyrrolizidine alkaloid retrorsine on hepatocytes in the resident liver while transplanted hepatocytes proliferate. In this study, we exploit this novel approach to address the important and controversial issue of whether hepatocytes, when proliferating extensively, undergo dedifferentiation and give rise to foci of undifferentiated hepatocytes. Genetically marked hepatocytes (isolated from normal Dipeptidyl peptidase IV+ Fischer 344 rats) were delivered intraportally (2 x 10(6) cells) into the liver of retrorsine-treated Dipeptidyl peptidase IV- mutant Fischer 344 rats in conjunction with partial hepatectomy. Transplanted hepatocytes were detected histochemically or immunohistochemically, and cell proliferation was studied by in situ hybridization for histone-3 mRNA. Expression of alpha-fetoprotein (AFP) mRNA, a marker of hepatocyte dedifferentiation, was also revealed by in situ hybridization. One day after partial hepatectomy and hepatocyte transplantation, endogenous hepatocytes and oval cells expanding in the liver expressed histone-3 mRNA (cells had entered S phase); 2 days later, transplanted hepatocytes and nonparenchymal cells also expressed histone-3 mRNA. Although the majority of endogenous hepatocytes did not divide and became arrested as quiescent megalocytes, the exogenous hepatocytes, as well as newly formed small hepatocytes, most probably derived from liver progenitor cells, underwent extensive proliferation. After 7-14 days, the nonparenchymal cells stopped proliferating, but transplanted hepatocytes and small endogenous hepatocytes continued to proliferate for 1 month, forming foci of dividing parenchymal cells. Although many of the hepatocytes in clusters were in S phase (histone-3 mRNA positive), none expressed AFP mRNA. In contrast, high expression of AFP mRNA was observed in proliferating oval and transitional cells, forming duct-like structures of cytokeratin-19-positive cells. From these studies, we conclude that hepatocyte proliferation in the adult liver is not associated with dedifferentiation.

Induction of hepatic nodules in the rat by aristolochic acid.

Aristolochic acid (AA), used as an anti-inflammatory agent in the past, is known to be mutagenic and carcinogenic to several organs of the rat, including forestomach, renal pelvis and urinary bladder. However, despite the induction of DNA adducts in the liver, no carcinogenic potential of AA has been reported in the latter organ. The present study was based on the rationale that the lack of carcinogenicity of AA to the liver could be because this chemical may not be necrogenic at the doses examined and liver cell proliferation has been established as an essential component for initiation of liver carcinogenesis in the rat. The results indicated that AA is non-necrogenic to the rat liver. However, a single non-necrogenic dose of AA (10 mg/kg b.w., i.p.) given 18 hours after 2/3 partial hepatectomy initiated liver cell carcinogenesis. The initiated cells are promotable with 1% dietary orotic acid, a liver tumor promoter, to form glutathione-S-transferase 7-7 positive hepatic foci and nodules.

Studies on the effect of dietary orotic acid on mouse liver carcinogenesis induced by diethylnitrosamine.

The present study was designed to determine whether orotic acid, a liver tumor promoter in the rat, also promotes liver carcinogenesis in the mouse. Eight-week-old male BALB/c mice were initiated with diethylnitrosamine (90 mg/kg i.p.). One week later they were divided into 2 groups and given either a basal diet or the basal diet containing 1% orotic acid (OA). They were killed at 6 or 10 months after the administration of the carcinogen. At 6 months, no nodular lesions were seen in mice whether or not they were exposed to OA. However by 10 months 100% of mice in both groups developed hepatic nodules. OA neither shortened the latent period for the appearance of the nodular lesions not did it increase the size of the nodules. Although BALB/c mice exhibited an increase in uridine nucleotides and a decrease in adenosine nucleotides in the liver upon exposure to OA, the magnitude of the change was less compared with that seen in the rat liver. The resistance of BALB/c mouse to the tumor-promoting effects of OA may reflect in part the resistance of the mouse to OA-induced nucleotide pool imbalance.

Sequential histopathological analysis of hepatocarcinogenesis in rats during promotion with orotic acid.

In the present study, sequential histopathological changes during hepatocarcinogenesis promoted by orotic acid were examined. Male Fischer 344 rats were given 1,2-dimethylhydrazine.2HCl (100 mg/kg, i.p.) 18 h after 2/3 partial hepatectomy. After 1 week of recovery, they were divided into 2 groups; group 1 was continued on a semisynthetic basal diet while the group 2 received the basal diet containing 1% orotic acid. Rats were sacrificed after 5, 10, 20, 29, 40 and 53 weeks of promotion. Histopathological analysis indicated that emergence of hepatocellular carcinomas was preceded first by foci of morphologically and histochemically altered hepatocytes and then by the appearance of hepatocyte nodules. Clear cell foci, eosinophilic ground glass foci and gamma-glutamyltransferase positive foci were detectable after 5 weeks in initiated rats fed orotic acid. Hepatocyte nodules developed in 56% of the rats after 20 weeks of promotion, while the first hepatocellular carcinoma was observed in one rat sacrificed after 29 weeks of orotic acid promotion. Cancer incidence steadily increased with the duration of the orotic acid treatment and 59% developed hepatocellular carcinomas with 30% metastasis to lungs by 53 weeks of promotion. A relevant feature of this model is that during exposure to orotic acid no liver hyperplasia, nor bile duct or oval cell proliferation were seen and the liver architecture in the tissue surrounding focal lesions was well preserved throughout the sequence.

An earlier proliferative response of hepatocytes in gamma-glutamyl transferase positive foci to partial hepatectomy.

One of the hallmarks of initiated hepatocytes is their resistance to several hepatotoxins. This property forms the basis for their selective growth under conditions which are inhibitory to the non-initiated hepatocytes. Selective growth of initiated hepatocytes also occurs, albeit at a low level, in initiated rat liver without exposure to any known promoting regimen and/or in the absence of any known selective pressure to which initiated hepatocytes can possibly be resistant. This latter phenotypic property of initiated hepatocytes was further characterized by comparing the kinetics of response of hepatocytes in gamma-glutamyl transferase positive foci and in the surrounding liver to 2/3 partial hepatectomy both in the presence and in the absence of a promoting regimen. Male Fischer 344 rats (130-150 g) were initiated with a single dose of diethylnitrosamine and 1 week later they were placed on either a semi-synthetic basal diet or a promoting diet containing 1% orotic acid. Partial hepatectomy was performed 15 weeks after initiation and animals from both groups were killed at 12, 16, 20, 24, 30, 36, 48, 72 or 96 h after operation. Each animal received a pulse of 3H-labelled thymidine 1 h prior to killing. Autoradiographic studies revealed that hepatocytes in gamma-glutamyl transferase positive foci in the livers of rats fed the basal diet were significantly labelled at 16 h post-partial hepatectomy while surrounding hepatocytes were still virtually quiescent (LI 12.7 +/- 4.7 versus 1.2 +/- 0.5%, respectively). Higher labelling index in foci compared to the surrounding liver was also seen at 20 h post-PH (36.9 +/- 2.6 versus 21.5 +/- 2.4). Similar earlier response of hepatocytes in gamma-glutamyl transferase positive foci was also seen in initiated rats exposed to dietary orotic acid. In addition, orotic acid treatment appears to have imposed a slight delay on the entry of hepatocytes in the surrounding liver into 'S' phase and thereby enhancing the differential of growth response between these two populations.

Early exposure to restraint stress enhances chemical carcinogenesis in rat liver.

This study examines the effect of a stress-associated condition on chemical hepatocarcinogenesis in the rat. Rats were given diethylnitrosamine (200 mg/kg. b.w., i.p.), followed, 1 week later, by three cycles of immobilization at room temperature. Two weeks after the last cycle they were treated according to the resistant hepatocyte protocol. At 4 weeks after selection, mean size of glutathione-S-transferase 7-7 positive foci/nodules was increased in the immobilized group (0.82+/-0.22 vs. 0.25+/-0.04 mm(2) in controls). Furthermore, at the end of 1 year 10/13 animals (77%) developed hepatocellular carcinoma in the former group, while only 6/14 (43%) incidence of cancer was found in controls. These results indicate that exposure to restraint stress early during carcinogenesis enhances the development of chemically-induced hepatocellular carcinoma in the rat.

One-step detection and genotyping of human papillomavirus in cervical samples by reverse hybridization.

This study describes a nonisotopic polymerase chain reaction-reverse hybridization-based method (PCR-RH) for the one-step detection and genotyping of anogenital human papillomavirus (HPV) in a microwell format. HPV DNA was amplified and labeled by PCR using GP5+/GP6+ primers. Labeled amplicons were hybridized to 20 HPV type-specific capture probes anchored to the surface of plastic microwells and detected by an immunoenzymatic assay. Assay sensitivity was <50 pg labeled amplicon, and no cross-reactivity was observed, as determined by hybridizing serial dilutions of labeled PCR products to either matched or mismatched capture probes. The assay was tested on 66 clinical samples (23 specimens with normal histology, I fibropapilloma, 26 cervical intraepithelial neoplasia grade 1 [CIN1], 9 CIN2, and 7 CIN3) and compared with a method based on restriction fragment length polymorphism (RFLP) of PCR products. PCR-RH and PCR-RFLP performed equally well on clinical samples. The overall HPV detection rate was similar: 65.1% (43/66) for PCR-RH and 57.6% (38/66) for PCR-RFLP. HPV DNA was found in all CIN2 and CIN3 samples by both methods; however, PCR-RH detected more positives among normal biopsy samples and CINI cases. Overall, there was good agreement between the two genotyping methods, but RH yielded fewer cases with undetermined HPV genotype.

Hepatic cholesterol in lead nitrate induced liver hyperplasia.

Wistar rats treated with lead nitrate were used in these experiments to provide evidence of the possible correlation between hyperplasia, induced cholesterol synthesis and the levels of glucose-6-phosphate dehydrogenase (G-6-PD) in the liver. Lead treatment increases liver weight, hepatic cholesterol esters and the relative content of free cholesterol. An increase of the incorporation of tritiated water in free and cholesterol esters was also observed. The effect of lead resulted in an increase of hepatic G-6-PD at all times considered. The correlation between these parameters and hyperplasia are discussed.

Altered growth pattern, not altered growth per se, is the hallmark of early lesions preceding cancer development.

Many human solid cancers arise from focal proliferative lesions that long precede the overt clinical appearance of the disease. The available evidence supports the notion that cancer precursor lesions are clonal in origin, and this notion forms the basis for most of the current theories on the pathogenesis of neoplastic disease. In contrast, far less attention has been devoted to the analysis of the phenotypic property that serves to define these focal lesions, i.e. their altered growth pattern. In fact, the latter is often considered a mere morphological by-product of clonal growth, with no specific relevance in the process. In the following study, evidence will be presented to support the concept that focal growth pattern is an inherent property of altered cells, independent of clonal growth; furthermore, it will be discussed how such a property, far from being merely descriptive, might indeed play a fundamental role in the sequence of events leading to the development of cancer. Within this paradigm, the earliest steps of neoplasia should be considered and analysed as defects in the mechanisms of tissue pattern formation.

The resistance phenotype in the development and treatment of cancer.

Phenotypic resistance, acquired early in carcinogenesis, has an established role in the pathogenesis of cancer in well-characterised experimental systems, and possibly also has a role in the origin of human cancer. It has been suggested that sunlight, an established risk factor for human skin carcinogenesis, is able to induce rare altered cells resistant to toxicity and to favour their clonal expansion via toxic effects exerted on normal keratinocytes. Other major risk factors for human neoplasia, including smoking and ageing, may also act partly through imposition of a constrained growth environment in the target organ to favour the emergence of altered resistant cells. Strategies aimed at counteracting this constrained environment could be effective in attenuating the force that sustains clonal expansion of altered cells.

Rat hepatocyte nodules are resistant to the necrogenic effect of D-galactosamine.

D-Galactosamine is a known hepatotoxin which induces liver cell necrosis via depletion of UTP and other uridine nucleotides. Our previous work indicated that nodular hepatocytes have higher levels of total uridine nucleotides compared to normal liver, and in the present study we investigate the effect of galactosamine treatment on hepatocyte nodules and surrounding liver. Hepatic nodules were generated in male Wistar rats according to the Solt and Farber protocol. Six months after initiation animals received a single injection of D-galactosamine (500 mg/kg i.p.) and were then killed 1, 2, 4 or 7 days later. Histological analysis of liver revealed the presence of extensive liver cell necrosis in normal tissue 1 and 2 days after galactosamine treatment. However, very little or no necrosis was detectable inside hepatic nodules at any time point, indicating that these focal areas are resistant to the cytotoxic effect of galactosamine. This type of resistance could be the expression of a new component in the resistant phenotype of hepatic nodules.

Transplantation of normal hepatocytes modulates the development of chronic liver lesions induced by a pyrrolizidine alkaloid, lasiocarpine.

Lasiocarpine (LC), a pyrrolizidine alkaloid, is able to induce a series of chronic and progressive lesions in rat liver, including a long-lasting block in the cell cycle, the appearance of enlarged hepatocytes (megalocytosis), fibrosis, cirrhosis and malignant neoplasma. In this study the effect of transplantation of normal hepatocytes on the development of LC-induced chronic lesions in rat liver was examined. Two-month-old male Fischer 344 rats were given a single dose of LC (80 mumol/kg i.p.). Four weeks later all animals were subjected to 2/3 partial hepatectomy (PH). In addition, at the time of PH one group of rats were transplanted with normal hepatocytes isolated from a syngeneic donor (10(6) cells/rats via the portal vein), while the other group received only the culture medium. All rats were killed 14 weeks after the operation. Grossly, the liver of rats exposed to LC followed by PH with no transplantation of normal hepatocytes was small in size (% liver wt/body wt 1.66 +/- 0.08) and exhibited a few whitish nodules. Histologically, approximately 88% of the liver section was occupied by enlarged hepatocytes and hepatocyte nodules composed of smaller hepatocytes developed in every animal in this group. In addition, extensive bile ductular proliferation was present. However, the liver of rats that were similarly treated but received normal hepatocytes were significantly larger in size (% liver wt/body wt 2.16 +/- 0.07) and were almost completely free of megalocytosis, bile ductular proliferation and hepatocyte nodules. These findings indicate that transplantation of normal hepatocytes is able to modulate the development of chronic liver lesions induced by LC and may be relevant to the pathogenesis of progressive liver diseases such as neoplasia and cirrhosis.

Principles of therapeutic liver repopulation.

Recently, it has been shown in several animal models that more than 90% of host hepatocytes can be replaced by a small number of transplanted donor cells in a process we term therapeutic liver repopulation. This phenomenon is analogous to repopulation of the hematopoietic system after bone marrow transplantation. Liver repopulation occurs when transplanted cells have a growth advantage in the setting of damage to recipient liver cells. Here we review the current knowledge of this process and discuss the hopeful implications for treatment of liver diseases.

Effect of 3-MC on cholesterolemia and hepatic G-6-PD.

The effect of 3-methylcholanthrene (3-MC), an inducer of the mixed function oxidases system (MFOS), was investigated in male Wistar rats in relation to plasmatic cholesterol and hepatic glucose-6-phosphate dehydrogenase (G-6-PD). 3-MC induced an increase in total cholesterol; the maximal increase was seen 2 days after treatment (50%). The increase in total cholesterol was followed by an augmentation in cholesterol HDL. 3-MC treatment resulted also in an increase of hepatic G-6-PD.

Inhibition of DNA synthesis in primary cultures of hepatocytes by orotic acid.

Orotic acid has been shown to promote carcinogenesis in the liver and the intestine of the rat. In an attempt to determine whether orotic acid promotes liver carcinogenesis by creating differential mitoinhibition, experiments were designed to study the effect of orotic acid on the labeling index of isolated hepatocytes in response to epidermal growth factor. The results indicated that orotic acid added in vitro inhibited epidermal-growth-factor-induced labeling index of isolated hepatocytes. In addition, isolated hepatocytes from rats exposed to orotic acid under promoting conditions also exhibited a decreased response to epidermal growth factor. These data suggest that orotic acid may exert its promoting effect by differentially inhibiting the response of normal hepatocytes to one or more endogenous growth stimuli while permitting the initiated hepatocytes to respond to such stimuli and grow to form hepatic nodules.

Increasing the interval between initiation and the onset of exposure to orotic acid decreases its promoting effect on rat liver carcinogenesis.

The present study was designed to determine whether a delay in the start of the promoting regimen after the administration of a carcinogen would influence the promoting efficacy of orotic acid on the development of hepatocellular carcinoma in rats. Male Fischer 344 rats weighing 130-150 g were injected with a single dose of diethylnitrosamine (200 mg/kg body wt i.p.) then divided into 3 groups: groups 1 and 2 were given semi-synthetic basal diet or the same diet containing 1% orotic acid (OA) respectively starting 1 week after the carcinogen; group 3 received the OA diet starting 5 weeks after the administration of diethylnitrosamine. Animals from these 3 groups were sacrificed after 25, 32, 42 and 60 weeks of being fed their respective diets. The results indicated that delaying the start of the OA diet after the carcinogen resulted in about a 50% decrease in the incidence of hepatic nodules and/or hepatocellular carcinomas at various time points during the experiment. This decrease in promoting efficacy of OA was not apparently explainable by lack of metabolic effects of OA, at least in terms of induction of nucleotide pool imbalance, a condition that appears to be important for OA to exert its tumor promoting effects.

The development of hepatocellular carcinoma in initiated rat liver after a brief exposure to orotic acid coupled with partial hepatectomy.

Previous work from this laboratory has revealed that a minimum of 10-20 weeks of continuous exposure to 1% dietary orotic acid (OA) is necessary for this regimen to exert a significant promoting effect on the carcinogenic process in rat liver. The present study investigates the effect of partial hepatectomy (PH), given during a short-term exposure (4 weeks) to OA, on the development of hepatocyte nodules (HN) and hepatocellular carcinoma (HCC) initiated by diethylnitrosamine (DEN). Male Fischer 344 rats (130-150 g) were given a single dose of DEN (200 mg/kg body wt i.p.). Starting a week later they were fed either a semisynthetic basal diet (BD) or the same diet containing 1% OA for 2 weeks; two-thirds PH was then performed followed by another 2 weeks of BD or OA diet respectively. At the end of this treatment some animals from both groups were killed while the rest were continued on BD and killed at 20 or 56 weeks thereafter. The results showed no difference between the two groups in the incidence of gamma-glutamyltransferase-positive foci when rats were killed at 2 weeks after PH. However, 4 week exposure to OA coupled with PH significantly enhanced the incidence of HN and HCC when this protocol was followed by 20 or 56 weeks of BD feeding respectively, leading to 63% incidence of HCC in the OA-fed group, while no HCC was observed in control animals. It is concluded that a type of stable or permanent change(s) ('imprinting' or 'memory effect') is induced in the initiated rat liver by this treatment, which imposes a promoting environment in the liver even after withdrawal of the promoter.

The effect of long-term feeding of orotic acid on the incidence of foci of enzyme-altered hepatocytes and hepatic nodules in Fischer 344 rats.

The present study was designed to determine the long-term effects of orotic acid (OA), a multi-organ tumor promoter, in rats not exposed to any carcinogen. Male Fischer 344 rats (130-150 g) were divided into two groups and given either a semisynthetic basal diet (BD) or the same diet containing 1% OA. Animals from both groups were killed after 1 or 2 years of treatment. Foci of placental glutathione-S-transferase (GST 7-7) positive hepatocytes were observed in the livers of both BD and OA fed rats killed after 1 year. However, they were more in number in animals receiving OA (156 +/- 21 versus 51 +/- 11/cm3). After 2 years, hepatic nodules were seen in almost all the animals given OA and in approximately 30% of the rats given BD. The nodules were of two main types: (i) a reddish-brown type, present in 85% of rats exposed to OA and in 27% of rats given BD, and (ii) a greyish-white type, found in 50% of animals fed OA and in none of the animals fed BD. These two types of lesions were also histologically different. Reddish-brown nodules were composed of slightly enlarged hepatocytes resembling normal surrounding tissue, while greyish-white nodules were similar in structure and are indistinguishable from hepatic nodules induced by genotoxic chemical carcinogens. The results are interpreted to suggest that the foci/nodules seen in OA-fed rats are due to a promoting effect of OA on spontaneously arising and/or diet-induced altered cells.

Studies on liver tumor promotion in the rat by orotic acid: dose and minimum exposure time required for dietary orotic acid to promote hepatocarcinogenesis.

Our earlier studies indicated that orotic acid, a precursor for pyrimidine nucleotide biosynthesis, exerts a promoting effect on rat hepatocarcinogenesis. The present study was designed to determine the optimum conditions of exposure to orotic acid required for promotion of hepatocarcinogenesis in the initiated rats. The first series of experiments was designed to determine the optimum dose of orotic acid needed to exert its liver tumor promoting effect. Accordingly male Fischer rats were given diethylnitrosamine (200 mg/kg, i.p.) or 0.9% NaCl. One week later carcinogen-injected rats were divided into six groups and fed either basal diet or the same diet containing 0.1, 0.5, 1, 2 or 4% orotic acid. Rats given 0.9% NaCl were fed 4% orotic acid. Two-thirds partial hepatectomy was performed on all animals 10 weeks after starting on their respective diets, and all groups were killed 3 weeks thereafter. Analysis of gamma-glutamyltransferase-positive foci and nodules revealed that 0.5-1% orotic acid in the diet is sufficient to exert a significant promoting effect on the selective growth of initiated hepatocytes, while higher concentrations of orotic acid were only marginally more effective. No gamma-glutamyltransferase-positive foci were observed in animals given 4% orotic acid diet following saline injection. Using 1% orotic acid as the promoting regimen, in the next series, the minimum exposure time required for dietary orotic acid to promote liver carcinogenesis was determined. Male Fischer 344 rats were given i.p. either 1,2-dimethylhydrazine dihydrochloride (100 mg/kg) or 0.9% NaCl 18 h after 2/3 partial hepatectomy. After 1 week of recovery one group of rats was continued on a semisynthetic basal diet, while others were transferred to the same basal diet containing 1% orotic acid. Rats that were on the 1% orotic acid diet were progressively transferred to the basal diet after 5, 10, 20, 29 and 40 weeks of exposure. All rats were sacrificed 54 weeks after the beginning of the experiment. The results indicate that 100% of the initiated rats developed hepatic nodules whether or not they were exposed to an orotic acid-containing diet. However, the incidence of hepatocellular carcinoma was greatly increased in animals exposed to the orotic acid diet, with 42% incidence in initiated rats given orotic acid diet for 10 weeks and up to 75% in those exposed to this diet for 40 weeks. Further, promotion by orotic acid exhibited a high metastatic potential with 33-60% metastasis to the lungs.(ABSTRACT TRUNCATED AT 400 WORDS)

Perturbations of endogenous levels of orotic acid and carcinogenesis: effect of an arginine-deficient diet and carbamyl aspartate on hepatocarcinogenesis in the rat and the mouse.

Feeding excess orotic acid (OA) in the diet promotes the carcinogenic process in different organs including the liver. A number of metabolic and genetic disorders are associated with increased synthesis of endogenous OA and some of these disorders appear to pose an increased risk of liver cancer development. This study therefore examines whether excess OA of endogenous origin also exerts a promoting effect on hepatocarcinogenesis in the mouse and the rat. Increased endogenous synthesis of OA was achieved by (i) feeding a diet deficient in arginine (AD) and (ii) feeding excess dietary carbamylaspartate (CA), a precursor for the synthesis of OA. A single dose of diethylnitrosamine (DENA) was given i.p. to male Fischer 344 rats (200 mg/kg) or to male DBA/2 mice (90 mg/kg). One week later they were placed on either AD diet or the same diet supplemented with 1.35% arginine (AS) for a total of 4 weeks. Two-thirds partial hepatectomy (PH) was performed at the end of the second week. All animals were then transferred to a control semisynthetic basal diet for a total of 20 weeks before they were killed. The results indicated that AD diet increased the incidence of hepatic nodules in both rats (percentage area occupied by nodules was 4.7 +/- 0.4 in the AD group compared to a control value of 0.7 +/- 0.5) and mice (4/10 mice had nodules > 5 mm diameter in the AD group while none in the AS group had such large nodules). In another experiment male Fischer 344 rats similarly initiated with DENA were exposed to either basal diet or basal diet containing 2% CA for 4 weeks coupled with PH performed at the end of the second week. This regimen was followed by 20 weeks of feeding basal diet to both groups. Rats given CA developed larger hepatic foci and nodules (0.84 +/- 0.56 mm3) compared to the control group, which was fed basal diet throughout the experiment (0.07 +/- 0.03 mm3). Further, both AD diet and dietary CA, like dietary OA, induced an increase in hepatic uridine nucleotides. Taken together, these results suggest that increased levels of endogenously synthesized OA, like exogenously supplied excess OA, can induce an imbalance in hepatic nucleotide pools and can exert a promoting effect on hepatocarcinogenesis.