Transgenic mice that overproduce the hepatitis B virus large envelope polypeptide and accumulate toxic quantities of hepatitis B surface antigen (HBsAg) within the hepatocyte develop severe, prolonged hepatocellular injury that initiates a programmed response within the liver, characterized by inflammation, regenerative hyperplasia, transcriptional deregulation, and aneuploidy. This response inexorably progresses to neoplasia. The incidence of hepatocellular carcinoma in this model corresponds to the frequency, severity, and age of onset of liver cell injury, which itself corresponds to the intrahepatic concentration of HBsAg and is influenced by genetic background and sex. Thus, the inappropriate expression of a single structural viral gene is sufficient to cause malignant transformation in this model. These results suggest that severe, prolonged cellular injury induces a preneoplastic proliferative response that fosters secondary genetic events that program the cell for unrestrained growth.

The tumorigenic activity of manufactured gas plant residue (MGP) was evaluated in female A/J mice using a F0927 basal gel diet system. Adulterated diets containing MGP (0.10% or 0.25%) or benzo[a]pyrene (B[alpha]P; 16 or 98 ppm) were fed for 260 days. A negative control group was maintained on a nonadulterated basal gel diet. Mice dosed with a single ip injection of 1.79 mg of B[a]P in a tricaprylin vehicle and maintained on a NIH-07 pellet diet were positive controls. In addition, a nontreated group of mice and a group dosed with vehicle only were maintained on a NIH-07 pellet diet and used as negative controls. Animal body weight and consumption of MGP and B[a]P were monitored throughout the study. Ingestion of a 0.10 or 0.25% MGP adulterated diet resulted in 70 and 100% of the mice developing lung tumors with a multiplicity of 1.19 and 12.17 tumors/mouse, respectively. Mice maintained on a 0.10% MGP diet consumed 0.7 g of MGP containing 1.8 mg of B[a]P while those fed a 0.25% MGP diet ingested 1.5 g of MGP containing 4.2 mg of B[a]P. The incidence of lung tumors in mice fed only B[a]P was considerably lower than that observed for animals fed a MGP diet. A diet containing 98 ppm B[a]P produced a significant incidence of tumor-bearing mice with 52% developing lung tumors. The multiplicity observed in these animals, however, was not significant at 0.59 tumors/mouse. A diet containing 16 ppm B[a]P did not produce a significant tumorigenic response in lung. Animals fed a 16 or 98 ppm B[a]P diet consumed a total of 11 and 67 mg of B[a]P, respectively. A single ip dose of B[alpha]P (1.79 mg in 0.25 mL of tricaprylin) resulted in 100% lung tumorigenesis with a multiplicity of 15.79 tumors/mouse. In contrast to observed induction of lung tumors, no forestomach tumors were detected in any animal fed a 0.10 or 0.25% MGP adulterated diet. However, ingestion of a diet containing only 16 or 98 ppm of B[a]P resulted in 20 and 100% of the mice developing forestomach tumors, respectively. The multiplicity for forestomach tumors was 0.24 and 4.22 tumors/mouse, respectively. The incidence of forestomach carcinomas in tumor bearing mice was 8 and 52%, respectively. The ip administration of 1.79 mg of B[a]P resulted in an 83% forestomach tumor incidence having a multiplicity of 1.83 tumors/mouse. Forestomach carcinomas were induced in 34% of the mice exhibiting forestomach tumors. These data indicate that chronic ingestion of MGP- or B[a]P-adulterated diets produces significant differences in the tumorigenic response of female A/J mouse forestomach and lung tissues.

The identification of ductal plate cells as likely progenitors for bile duct epithelium and hepatocytes and their possible reappearance as oval cells in the regenerating liver have generated much interest in their pluripotential capacities. We have examined the distribution of three hematopoietic stem cell markers, c-kit, CD34, and CD33 in addition to laminin, the standard cytokeratin markers CAM 5.2, CK 18, and CK 7 and the oval cell marker OV-6 in fetal liver during various stages of development. Hematopoietic stem cell markers were expressed in ductal plate cells in a pattern similar to the early cytokeratin markers CAM 5.2 and CK 18. Cells stained strongly for these early cytokeratin markers until 22 weeks. Thereafter, the expression of these markers decreased while positivity for CK 7 increased. Bile duct cells showed a distribution of hematopoietic and cytokeratin markers resembling that of ductal plate cells. Both ductal plate cells and bile duct cells expressed OV-6 strongly throughout development. This study showed similarity between hepatic and bile duct precursors and bone marrow stem cells. The comparable distribution of markers in bile duct epithelium and ductal plate cells may imply fewer transitional stages between ductal plate cells and bile duct epithelium than between the putative stem cells and hepatocytes.

Covalent DNA addition products (adducts) formed by the reaction of chemical carcinogens or their metabolites with DNA are critically involved in the initiation of chemical carcinogenesis and may serve as molecular markers and dosimeters for environmental carcinogen exposures. Using a highly sensitive 32P-postlabeling assay for DNA adduct analysis, we studied DNA damage elicited by cigarette smoke in tissues of smokers. A multitude of characteristic smoking-induced, presumably aromatic DNA adducts were found to occur in a dose- and time-dependent manner in the lung, bronchus, and larynx of smokers with cancer of these organs and to decline only slowly after cessation of smoking. Low levels of adducts appeared to persist for up to 14 years in the lungs of exsmokers with high previous exposures. These results corroborate data of epidemiological studies showing that the lung cancer risk and mortality of smokers increase with the intensity and duration of smoking and decline only slowly after cessation of smoking. Tissue distribution studies in autopsy samples revealed the presence of smoking-associated DNA lesions also in the kidney, bladder, esophagus, heart, ascending aorta, and liver. The most extensive DNA damage was found in lung and heart, i.e., 1 aromatic adduct in about 10(7) DNA nucleotides. Our results suggest that cigarette smoking-induced DNA adduct formation is causally related to cancer in the target organs.

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We have recently reported that cell lines of nonparenchymal origin isolated from rat liver and pancreas, which have been suggested to be the progeny of a facultative stem cell compartment in vivo, express an unusual combination of keratins (K). These cell lines express K8 and K14 but not K18 and K5, their normal partners in filament formation (Bisgaard HC, Thorgeirsson SS, J Cell Physiol 147:333-343, 1991). However, upon spontaneous transformation and differentiation toward a hepatoblastlike progeny, K14 expression is abrogated and replaced by expression of K18 (Wirth et al., Electrophoresis 13:305-332, 1992). In the study presented here, we confirmed by protein sequence analysis that K14 was a major component of the intermediate filaments in a nonparenchymal cell line of hepatic origin. Immunocytochemical analysis of the cells in monolayer demonstrated that K8 as well as K14 were incorporated in the cellular cytoskeleton. Further analysis by immunoprecipitation showed that filament complexes were formed between K8 and K14 as atypical partners. Thus, we concluded that in some nonparenchymal cell lines isolated from rat liver, K8 and K14 form a major intermediate filament network. Finally, we showed that an antibody widely used in studies of the cell lineages of hepatic and pancreatic tissues and their neoplasms, the mouse monoclonal antibody OV-6, recognizes a common epitope in K14 and K19.

Traditionally half of the cell population of the adult parathyroid gland is considered to be stromal fat. A marked decrease of stromal fat has been observed at autopsy of adult patients, the functional significance of which is unknown. In order to investigate this phenomenon, the stromal and parenchymal fat of the parathyroid glands of 33 adult patients who died with no known hormonal abnormalities were evaluated. Stromal fat was much less than 50 per cent, i.e., less than 10 per cent., in the majority of cases, while parenchymal fat was ample in all cases. This finding, especially if compared to cases with hyperparathyroidism, indicates the lack of functional specificity of change in stromal fat, whereas, alteration in parenchymal fat appears to be a better anatomical register of normal or abnormal parathyroid function.

Magnetic resonance (MR) imaging, localized in vivo proton spectroscopy, and T1 relaxation measurements were obtained from the livers of rats treated chronically with carbon tetrachloride and phospholipase D. The MR data correlated well with lipid changes measured biochemically and histologically. MR images appeared generally hyperintense during fatty infiltration, changing to hypointense mottling during cirrhosis. Water T1 relaxation times showed no statistically significant change at any time during the experiments from the control value of 908 ms (SE = 42 ms). Minor changes in lipid T1 values with time were noted. The average lipid T1 curve demonstrated a linear relation with time (r = 0.81), increasing from the control value of 283 ms (+/- 16 ms) to 365 ms (+/- 53 ms) at the end of the third week and decreasing slightly through the end of the experiment. Water-suppressed in vivo spectra showed quantitative changes in liver lipids which correlated well with the biochemical and histologic analysis. From the MR images and spectroscopy results it was possible to distinguish early fatty liver from more advanced cirrhosis.