Biomedical subjects

A Kopp-Schneider

Publications and source records attributed to A Kopp-Schneider.

At least 19 recordsLinked to original sources

PubMed2001

Identification of human renal cell carcinoma associated genes by suppression subtractive hybridization.

Renal cell carcinoma (RCC) are frequently chemo- and radiation resistant. Thus, there is a need for identifying biological features of these cells that could serve as alternative therapeutic targets. We performed suppression subtractive hybridization (SSH) on patient-matched normal renal and RCC tissue to identify variably regulated genes. 11 genes were strongly up-regulated or selectively expressed in more than one RCC tissue or cell line. Screening of filters containing cancer-related cDNAs confirmed overexpression of 3 of these genes and 3 additional genes were identified. These 14 differentially expressed genes, only 6 of which have previously been associated with RCC, are related to tumour growth/survival (EGFR, cyclin D1, insulin-like growth factor-binding protein-1 and a MLRQ sub-unit homologue of the NADH:ubiquinone oxidoreductase complex), angiogenesis (vascular endothelial growth factor, endothelial PAS domain protein-1, ceruloplasmin, angiopoietin-related protein 2) and cell adhesion/motility (protocadherin 2, cadherin 6, autotaxin, vimentin, lysyl oxidase and semaphorin G). Since some of these genes were overexpressed in 80-90% of RCC tissues, it is important to evaluate their suitability as therapeutic targets.

Biomarkers, Tumor↗

PubMed2001

Modeling cancer detection: tumor size as a source of information on unobservable stages of carcinogenesis.

This paper is concerned with modern approaches to mechanistic modeling of the process of cancer detection. Measurements of tumor size at diagnosis represent a valuable source of information to enrich statistical inference on the processes underlying tumor latency. One possible way of utilizing this information is to model cancer detection as a quantal response variable. In doing so, one relates the chance of detecting a tumor to its current size. We present various theoretical results emerging from this approach and illustrate their usefulness with numerical examples and analyses of epidemiological data. An alternative approach based on a threshold type mechanism of tumor detection is briefly described.

Computer Simulation↗

PubMed2001

Aberrant cyclooxygenase isozyme expression in human intrahepatic cholangiocarcinoma.

METHODS: Cellular localisation of the cyclooxygenase (COX) isozymes COX-1 and COX-2 was analysed in 24 cholangiocarcinomas, including 17 matched tissues originating from non-tumorous liver tissue adjacent to tumours and seven biopsies of normal human liver, by immunohistochemistry using isozyme selective antibodies. RESULTS: In normal liver, constitutive expression of COX-2 protein was a characteristic feature of hepatocytes whereas no COX-2 immunosignal was detectable in normal bile duct epithelium, Kupffer, and endothelial cells. In cholangiocarcinoma cells, COX-2 protein was strongly expressed at high frequency. The intensity, percentage of positive cells, and pattern of COX-2 expression were found to be independent of the stage of tumour differentiation. In hepatocytes of matched non-tumorous tissue, COX-2 expression was unaltered. In contrast, strong COX-1 expression was frequently localised to Kupffer cells, endothelial cells, and occasionally to hepatocytes, but not to bile duct epithelial cells. In approximately half of moderately and poorly differentiated but not well differentiated cholangiocarcinomas, weak to moderate COX-1 staining was found in tumour cells while COX-1 expression in Kupffer cells was much more pronounced. CONCLUSION: Aberrant COX-2 expression occurs during the early stage while COX-1 over expression seems to be related to later stages of cholangiocarcinogenesis.

Adult↗

PubMed2001

Significance of hepatic preneoplasia for cancer chemoprevention.

Hepatic preneoplasia represents an early stage in neoplastic development, preceding both benign and malignant neoplasia. This applies particularly to foci of altered hepatocytes (FAH), that precede the manifestation of hepatocellular adenomas and carcinomas in all species investigated. Morphological, microbiochemical and molecular biological approaches in situ have provided evidence for striking similarities in specific changes of the cellular phenotype of preneoplastic FAH emerging in experimental and human hepatocarcinogenesis, irrespective of whether this was elicited by chemicals, hormones, radiation, viruses or, in animal models, by transgenic oncogenes or Helicobacter hepaticus. Different types of FAH have been distinguished and related to three main preneoplastic hepatocellular lineages: (1) the glycogenotic-basophilic cell lineage, (2) its xenomorphic-tigroid cell variant, and (3) the amphophilic-basophilic cell lineage. The predominant glycogenotic-basophilic and tigroid cell lineages develop especially after exposure to DNA-reactive chemicals, radiation, hepadnaviridae, transgenic oncogenes and local hyperinsulinism, their phenotype indicating initiation by insulin or insulinomimetic effects of the oncogenic agents. In contrast, the amphophilic cell lineage of hepatocarcinogenesis has been observed mainly after exposure of rodents to peroxisome proliferators that are not directly DNA-reactive or to hepadnaviridae, the biochemical pattern mimicking an effect of thyroid hormone, including mitochondrial proliferation and activation of mitochondrial enzymes. Hepatic preneoplastic lesions are increasingly used as end-points in carcinogenicity testing, particularly in medium-term carcinogenesis bioassays. This has been complemented more recently by the use of FAH as indicators of chemoprevention, although possible pitfalls of this approach have to be considered carefully. Our ever-increasing knowledge on the metabolic and molecular changes that characterize preneoplastic lesions and their progression to neoplasia provides a new basis for rational approaches to chemoprevention by drugs, hormones or components of the diet.

Animals↗

PubMed2000

A model for hepatocarcinogenesis with clonal expansion of three successive phenotypes of preneoplastic cells.

The two-stage model with clonal expansion of intermediate cells has often been used to describe the carcinogenesis process. The model hypothesizes that cells have to undergo two mutations on their way from the normal to the malignant stage. Biological experiments indicate the existence of three types of preneoplastic cells in hepatocarcinogenesis representing three successive intermediate stages in the development of malignant cells from normal cells. This finding suggests that hepatocarcinogenesis should be described by a multi-stage model with three intermediate stages, leading to a four-stage mutation model with clonal expansion of all types of intermediate cells. This model is presented and mathematical approximations for the number and size of nonextinct premalignant clones of the different cell types are derived. The model is applied to focal lesion data from a rat hepatocarcinogenesis experiment.

Animals↗

PubMed2000

Hepadnaviral hepatocarcinogenesis: in situ visualization of viral antigens, cytoplasmic compartmentation, enzymic patterns, and cellular proliferation in preneoplastic hepatocellular lineages in woodchucks.

BACKGROUND/AIMS: Hepadnaviral hepatocarcinogenesis induced in woodchucks with and without dietary aflatoxin B1 has been established as an appropriate animal model for studying the pathogenesis of human hepatocellular carcinoma in high-risk areas. Our aim in this study was the elucidation of phenotypic cellular changes in early stages of this process. METHODS: Woodchucks were inoculated as newborns with woodchuck hepatitis virus (WHV), and partly also exposed to aflatoxin B1. Sequential hepatocellular changes in the expression of viral antigens, ultrastructural organization, cellular proliferation and apoptosis were studied in situ by electron microscopy, enzyme and immunohistochemistry. RESULTS: A characteristic finding in WHV-infected animals (with and without aflatoxin B1) was proliferative areas of minimal structural deviation, which predominated periportally, comprised glycogen-rich, amphophilic, and ground-glass hepatocytes, and expressed the woodchuck hepatitis core and surface antigens. Two main types of proliferative foci emerged from minimal deviation areas, glycogenotic clear cell foci and amphophilic cell foci (being poor in glycogen but rich in mitochondria), giving rise to the glycogenotic-basophilic and the amphophilic preneoplastic hepatocellular lineages. A gradual loss in the expression of viral antigens appeared in both lineages, particularly early in the glycogenotic-basophilic cell lineage. Whereas glycogenosis was associated with an enzymic pattern suggesting an early activation of the insulin-signaling pathway, amphophilic cells showed changes in enzyme activities mimicking a response of the hepatocytes to thyroid hormone, which may also result from early changes in signal transduction. CONCLUSION: Preneoplastic hepatocellular lineages in hepadnaviral and chemical hepatocarcinognesis show striking phenotypic similarities, indicating concordant and possibly synergistic early changes in signaling.

Aflatoxin B1↗

PubMed2000

Modulation of benzo[a]pyrene diolepoxide-DNA adduct levels in human white blood cells by CYP1A1, GSTM1 and GSTT1 polymorphism.

The modulation of benzo[a]pyrene diolepoxide (BPDE)-DNA adduct levels by polymorphisms in the CYP1A1, GSTM1 and GSTT1 genes was assessed in leukocytes of Caucasian males. Eighty-nine coke oven workers (35 smokers, 36 ex-smokers and 18 non-smokers) were recruited from job categories with different exposure levels to polycyclic aromatic hydrocarbons (PAH), together with 44 power plant workers (all smokers) not exposed to PAH. BPDE-DNA adducts were detected in 69 of 133 (52%) DNA samples with a 100-fold variation (range 0.2-44 adducts/10(8) nt) and a median of 1.6 adducts/10(8) nt. All samples with the GSTM1 active genotype (n = 59) and five out of 74 samples with GSTM1*0/*0 (7%) showed non-detectable adducts (<0.2 adducts/10(8) nt) and 69 of 74 subjects with GSTM1*0/*0 (93%) had detectable adducts (>0.2 adducts/10(8) nt). The difference in adduct level between the GSTM1*0/*0 and GSTM1 active genotypes was highly significant (P < 0.0001). No significant difference in adduct level between the GSTT1*0/*0 and GSTT1 active genotypes was seen. All heterozygotes (CYP1A1*1/*2) from subjects of GSTM1 active type did not have detectable adducts. Among the GSTM1-deficient individuals (n = 69), 42 with the CYP1A1*1/*1 genotype showed a lower adduct level (median 1.3, range 0.2-4.1 adducts/10(8) nt) compared with 26 individuals with heterozygous mutated CYP1A1*1/*2 genotypes (median 2.5, range 0.4-6.1 adducts/10(8) nt, P < 0.015). One individual with low PAH exposure and the rare combination CYP1A1*2A/*2A-GSTM1*0/*0 showed an extremely high level of 44 adducts/10(8) nt. Significant differences in detectable adduct levels were found between the CYP1A1*1/*1 and CYP1A1*1/*2 genotypes in the exposed group low + medium (P = 0.01) and for all adduct levels, detectable and non-detectable (set at a fixed value), in highly exposed individuals and in ex-smokers (P = 0.03), whereas no such differences were observed in the control group. Mutated CYP1A1*1/*2 increased the adduct level in non-smokers from the exposed group (1.4 versus 2.2 adducts/10(8) nt), but had no effect on the smokers from the exposed group (2.3 versus 2.8 adducts/10(8) nt). When all variables were dichotomized, statistical evaluation showed that CYP1A1 status (P = 0.015), PAH exposure (P = 0.003) and smoking (P = 0.006) had significant effects on adduct levels which increased in the order: CYP1A1*1/*1 < CYP1A1(*1/*2 or *2A/*2A); environmental exposure < occupational exposure; non-smokers < smokers, whereby adducts increased with cigarette dose and the duration of smoking. Higher levels of BPDE-DNA adducts in individuals with the combined CYP1A1(1/*2 or *2A/*2A)-GSTM1*0/*0 genotype suggest that these genotype combinations are at increased risk for contracting lung cancer when exposed to PAH.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗

PubMed1999

Mutational activation of the beta-catenin proto-oncogene is a common event in the development of Wilms' tumors.

Activation of beta-catenin-mediated transcription is the nuclear end point of organ-specific Wnt signaling. In the developing kidney, Wnt-4, a secreted glycoprotein, acts as an autoinducer of the mesenchymal to epithelial transition that underlies normal nephron development. Dysregulation of this epithelial transformation process may lead to Wilms' tumors (WTs). In this study, we investigated the potential role of the beta-catenin proto-oncogene, a candidate downstream target molecule of Wnt-4 signaling, in the development of WTs. In 6 of 40 tumors (15%), mutation analysis revealed heterozygous missense mutations or small deletions that result in the loss of important regulatory phosphorylation sites within the beta-catenin protein. These findings indicate that activating beta-catenin mutations may play a significant role in the development of WTs and establish a direct link between Wilms' tumorigenesis and the Wnt signal transduction pathway governing normal kidney development.

Cytoskeletal Proteins↗

PubMed1999

Threshold dose response for tumor induction by genotoxic carcinogens modeled via cell-cycle delay.

Dose-response relationships for tumor induction in animal bioassays for carcinogenicity are often postulated to include thresholds, particularly for nongenotoxic chemicals that increase the rate of cell proliferation at high doses. In this report, thresholds are postulated also for genotoxic carcinogens. The hypothesis is based on the idea of a delay of the cell cycle induced by low-level DNA damage and an acceleration at cytotoxic dose levels, thus resulting in a J-shaped (or U-shaped) dose response for cell turnover. Calculations were based on the 2-stage clonal expansion model of carcinogenesis. The background values chosen for the model parameters resulted in a 10.5% "spontaneous" 2-year cumulative tumor incidence. Using this as a starting point, a decrease by 3, 10, and 30% in the rates of cell turnover resulted in a decrease in the spontaneous tumor incidence to 9.4, 7.1 and 3.0%, respectively. Dose-responses with J-shaped curves for the rates of cell birth and death were modeled by shifted quadratic functions reaching the minimum at dose 1. Combinations with linearly increasing mutation rates also generated, under certain conditions, J-shaped dose-response curves for tumor incidence. As an example, for a 30% increase in mutation rates and a 10% decrease in cell turnover rates (both at dose 1), the dose-response curve showed an initial decrease of tumor incidence below the spontaneous rate, a reversion to the background value at 0.8 dose units, and an increase thereafter. The 0.8 dose could be considered to represent the "threshold dose." The approach presented might reconcile opposing views on thresholds on a biologically plausible mechanistic basis, and show a way for the quantitative estimation of threshold doses.

Animals↗

PubMed1998

Statistical models for low dose exposure.

Extrapolation of health risks from high to low doses has received a considerable amount of attention in carcinogenic risk assessment over decades. Fitting statistical dose-response models to experimental data collected at high doses and use of the fitted model for estimating effects at low doses lead to quite different risk predictions. Dissatisfaction with this procedure was formulated both by toxicologists who saw a deficit of biological knowledge in the models as well as by risk modelers who saw the need of mechanistically-based stochastic modeling. This contribution summarizes the present status of low dose modeling and the determination of the shape of dose-response curves. We will address the controversial issues of the appropriateness of threshold models, the estimation of no observed adverse effect levels (NOAEL), and their relevance for low dose modeling. We will distinguish between quantal dose-response models for tumor incidence and models of the more informative age/time dependent tumor incidence. The multistage model and the two-stage model of clonal expansion are considered as dose-response models accounting for biological mechanisms. Problems of the identifiability of mechanisms are addressed, the relation between administered dose and effective target dose is illustrated by examples, and the recently proposed Benchmark Dose concept for risk assessment is presented with its consequences for mechanistic modeling and statistical estimation.

Age Factors↗

PubMed1998

Localization of prostaglandin H synthase isoenzymes in murine epidermal tumors: suppression of skin tumor promotion by inhibition of prostaglandin H synthase-2.

The growth factor- and phorbol ester-inducible prostaglandin H synthase (PGHS)-2 has been found to be constitutively overexpressed in epidermal tumors generated by the initiation-promotion protocol in murine skin, whereas the expression of PGHS-1 does not change under these conditions. In this paper we report the intra-tumor distribution of the aberrantly expressed PGHS-2 and the cancer chemopreventive activity of a specific PGHS-2 inhibitor. By immunohistochemical methods using isoenzyme-specific antibodies, we found that the PGHS-1 protein was expressed in keratinocytes and Langerhans cells dispersed throughout the epithelial part of papillomas and squamous cell carcinomas and in inflammatory infiltrates occasionally seen in these tumors. A uniform pattern of PGHS-2 expression was observed in the basal keratinocytes of papillomas and in the follicular keratinocytes of carcinomas. In addition, Langerhans cells as well as tumor-associated inflammatory infiltrates exhibited PGHS-2-specific immunoreactivity. PGHS-2-catalyzed prostaglandin synthesis stimulated by the phorbol ester 12-O-tetradecanoylphorbol-13 acetate (TPA) in mouse epidermis in vivo was dose-dependently suppressed by topical administration of SC-58125, a specific PGHS-2 inhibitor. TPA-induced edema formation, epidermal DNA synthesis, and mitotic activity were not impaired by SC-58125 applied at a dose that inhibited TPA-induced prostaglandin E2 synthesis. However, the repetitive epicutaneous administration of SC-58125 substantially and significantly suppressed papilloma development. Malignant progression of papillomas was slightly retarded by the drug. These results indicate that aberrant expression of PGHS-2 in epidermal tumors may be a relevant target for prevention of epidermal cancer development in experimental animals and that the PGHS-2-specific inhibitor SC-58125, which is a potent inhibitor of tumor promotion in mouse skin, may be important for cancer chemoprevention in humans as well.

Animals↗

PubMed1998

A model for hepatocarcinogenesis treating phenotypical changes in focal hepatocellular lesions as epigenetic events.

The major paradigm for mathematically describing the carcinogenic process has been through the use of multistage models. Multistage models are made up of numerous compartments representing cells in various stages on the way to malignancy and where movement from one cell class to another is assumed to have exponential waiting time. Once a cell is in a particular class, clonal expansion through a linear birth-death process increases the size of the compartment. These models are characterized by movement of single cells from one compartment to another rather than clonal colonies of cells. However, there is some evidence to suggest that, in certain organs for certain types of agents, preneoplastic lesions with different phenotypes arise directly from an entire clonal colony rather than from a single cell within that colony. This manuscript describes a simple mathematical model of carcinogenesis using both persistent changes of single or several cells (to start the process) and shifting of colonies to describe the stages of the model. Likelihoods for the use of the model with data on colonies of preneoplastic lesions are described and applied to real data.

Animals↗

PubMed1998

Xenomorphic hepatocellular precursors and neoplastic progression of tigroid cell foci induced in rats with low doses of N-nitrosomorpholine.

Tigroid cell foci (TCF) are a well-defined entity induced in rat liver by chemical carcinogens, their significance for hepatocarcinogenesis being controversial. Using cytomorphological, cytochemical and morphometric approaches, we studied the evolution and fate of TCF sequentially from 7 to 110 weeks in groups of 50 male Sprague-Dawley rats, which remained untreated or received N-nitrosomorpholine (NNM) orally at concentrations of 3 and 1 mg/kg body wt/day for 7 and up to 75 weeks, respectively. An increased incidence of hepatocellular neoplasms developed in exposed animals compared with controls, which was significant for adenomas at both dose levels, and for carcinomas (HCC) after the longer exposure to the lower dose level (P < 0.0001). TCF appeared frequently in addition to other types of proliferative foci of altered hepatocytes (FAH) including clear/acidophilic and mixed cell foci (MCF) in NNM-treated and rarely in untreated rats. Striking similarities in the cellular phenotypes of TCF and many hepatocellular neoplasms indicated the potential of TCF for progression to both adenomas and carcinomas. TCF emerged from xenomorphic cell foci (XCF), which consisted of hypertrophied hepatocytes typically presenting an enlarged nucleus, abundant glycogen, smooth and rough endoplasmic reticulum, altered activities of several enzymes of carbohydrate metabolism and an increased cell proliferation (P < 0.001) compared with the extrafocal parenchyma. TCF shared many features with XCF, but their basophilia and proliferative activity was higher. The number of FAH appearing at the two dose levels of NNM was similar but the average size of TCF and MCF was frequently higher at late time points in the group developing a significantly higher incidence of HCC, which suggests a pronounced acceleration of neoplastic conversion in established preneoplastic cell populations rather than the induction of additional FAH by sustained effects of low doses of carcinogens.

Animals↗

PubMed1998

High benzo[a]pyrene diol-epoxide DNA adduct levels in lung and blood cells from individuals with combined CYP1A1 MspI/Msp-GSTM10/0 genotypes.

Levels of anti-benzo[a]pyrene diol-epoxide DNA adducts were analysed by high-pressure liquid chromatography/fluorimetric detection in non-tumorous lung tissues from 20 lung cancer patients and in white blood cells from 20 polycyclic aromatic hydrocarbon exposed coke oven workers. All were current tobacco smokers. CYP1A1 mutations (MspI at 6235 nt, Ile-Val462) and GSTM1 deletion polymorphisms in each individual were analysed in genomic DNA by PCR/restriction fragment length polymorphism. Independently of the CYP1A1 genotype (1) all 23 samples in the two groups with non-detectable adducts (< 0.2 per 10(8) nt) were of GSTM1 active genotype; (2) the 17 samples with detectable adducts (> or = 0.2 per 10(8) nt) in the two groups were GSTM1*0/*0. The difference in adduct levels between GSTM1*0/*0 and GSTM1 active genotype was highly significant (p < 0.00005). Among GSTM1-deficient individuals (n = 17), a subgroup of 14 individuals with CYP1A1*1/*1 (wild-type, n = 7) or heterozygous genotype (*1/*2A or *1/*2B, n = 7) showed low levels of BPDE DNA-adducts (range: 0.2-1.3 per 10(8) nt). (3) Three individuals with the rare combination CYP1A1*2A/*2A or *2A/*B and GSTM1*0/*0 showed significantly higher adduct levels (median: 17.4 adducts/10(8) nt, range 1.9-44; p = 0.017). Therefore, combination of homozygous mutated CYP1A1 and GSTM1*0/*0 genotypes lead, at a similar or even lower smoking dose, to a stronger increase of anti-benzo[a]pyrene diol-epoxide DNA adduct levels than found in individuals with CYP1A1 and GSTM1 wild-type. These data provide a mechanistic understanding of epidemiological studies that correlated these 'at risk' genotypes with increased smoking-related lung cancers.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗

PubMed1997

Carcinogenesis models for risk assessment.

This article provides an overview of different types of carcinogenesis models and discusses their use for risk assessment. One class of model, the multistage model, is especially suited for risk assessment purposes because it uses biological information about the process of carcinogenesis and the quantities of interest, such as time to tumour and number and size distribution of premalignant tumours, can be derived explicitly, allowing for standard statistical techniques to be used. The mathematical methods necessary for the treatment of multistage models are developed and the application of multistage models in risk assessment is discussed.

Carcinogens↗

PubMed1996

Calculating tumor incidence rates in stochastic models of carcinogenesis.

Multistage models of carcinogenesis are increasingly used in the estimation of risks from exposure to environmental agents. The two-stage model of carcinogenesis is routinely used because it agrees with much of the existing tumor incidence data, parallels the biological two-stage model, and has much of its mathematical details derived. However, recent findings on the mechanisms of carcinogenesis has led researchers to believe that there are a greater number of stages and a more complex structure to these models than a single pathway. In this paper, a method for readily computing tumor incidence rates for arbitrarily complex multistage models is derived. The formulas for the two-stage model with time-varying rates are given explicitly. Simple rules for more complicated models are given, and computer code able to implement these formulas are provided.

Animals↗

PubMed1996

Modeling the number and size of hepatic focal lesions following exposure to 2,3,7,8-TCDD.

Data on the size and number of placental glutathione S-transferase-positive (PGST+) foci were collected from a two-stage hepatocarcinogenesis model in female Sprague-Dawley rats. the study consisted of multiple 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-exposed dose groups including both diethylnitrosomine (DEN)-initiated and uninitiated animals. Groups were observed after 15 or 31 weeks of TCDD exposure. The parameters in the first half of a two-stage mathematical model of carcinogenesis were estimated from these data. If the model is valid, the results suggest that TCDD stimulates the production of PGST+ foci and promotes the growth of PGST+ foci. This finding suggests a complicated mechanism for TCDD-induced production of Hepatic foci that we refer to as activation, labeling TCDD as an activator. The analysis also indicates that there is an interaction between DEN and TCDD which results in dose-related formation of initiated cells throughout the study period. Best-fitting curves (using maximum likelihood methods) for TCDD-induced activation and promotion reached saturation levels at low doses of TCDD. In summary, the model fit the data well, but leads to an interpretation of the data which either questions the validity of the model or implies that our understanding of the effects of TCDD and DEN is incomplete.

Adenosine Triphosphate↗

PubMed1995

Synergistic hepatocarcinogenic effect of hepadnaviral infection and dietary aflatoxin B1 in woodchucks.

Interactive hepadnaviral and chemical hepatocarcinogenesis was studied in woodchucks inoculated as newborns with woodchuck hepatitis virus (WHV), which is closely related to the human hepatitis B virus. When the woodchucks reached 12 months of age, aflatoxin B1 (AFB1) was administered in the diet at dose levels of 40 micrograms/kg body weight/day for 4 months and subsequently 20 micrograms/kg body weight/day (5 days/week) for lifetime. WHV DNA was demonstrated by Southern blot hybridization in the serum and by PCR in the serum and/or liver tissue. The histo- and cytomorphology of the liver were investigated by light and electron microscopy. WHV carriers with and without AFB1 treatment developed a high incidence of preneoplastic foci of altered hepatocytes, hepatocellular adenomas, and hepatocellular carcinomas that appeared 6-26 months after the beginning of the combination experiment. Administration of AFB1 to WHV carriers resulted in a significantly earlier appearance of hepatocellular neoplasms and a higher incidence of hepatocellular carcinomas compared to WHV carriers not treated with AFB1. Neither hepatocellular adenomas nor carcinomas (but preneoplastic foci of altered hepatocytes) were detected in woodchucks receiving AFB1 alone, and no preneoplastic or neoplastic lesions were found in untreated controls. These results provide conclusive evidence of a synergistic hepatocarcinogenic effect of hepadnaviral infection and dietary AFB1. Except for the frequent presence of ground glass cells containing surface antigen filaments in the infected woodchucks, the phenotype of preneoplastic foci of altered hepatocytes was similar in WHV carriers with and without exposure to AFB1 and in animals treated with AFB1 alone. Clear cell foci excessively storing glycogen and/or fat, amphophilic cell foci crowded with mitochondria and peroxisomes, and mixed cell foci composed of various cell types including basophilic cells rich in ribosomes predominated. The cellular phenotype in neoplastic lesions varied from clear, amphophilic, and mixed cell populations in highly differentiated adenomas and carcinomas to basophilic cell populations prevailing in poorly differentiated carcinomas. The striking similarities in altered cellular phenotypes of preneoplastic hepatic foci emerging after both hepadnaviral infection and exposure to AFB1 suggest closely related underlying molecular mechanisms that may be mainly responsible for the synergistic hepatocarcinogenic effect of these oncogenic agents.

Aflatoxin B1↗