The sequential analysis of cancer development

A new mechanism of cancer initiation that involves the transformation of hepatocytes into preneoplastic single hepatocytes and minifoci positive for glutathione S-transferase P-form (GST-P) in rat livers: 3D analysis using a vibratome

BACKGROUND

Cancer initiation has long been "unknowable" in biology and medicine. In 1987, however, Moore and our research group observed single hepatocytes and minifoci that were strongly positive for glutathione S-transferase P-form (GST-P) in the rat liver as early as 2 to 3 days after initiation by diethylnitrosamine prior to the induction of GST-P+ foci and nodules. The induction of GST-P+ single hepatocytes, precursors of GST-P+ foci and nodules, was considered genetic. But, the details of the induction mechanism have remained unclear despite various examinations over a long period.

METHODS

Male Sprague-Dawley rats (aged 6 weeks) were fed a basal diet containing either benzyl isothiocyanate (BITC, 0.5% by wt) or 2-acetylaminofluorene (AAF, 0.04%) ad libitum for appropriate time intervals. All animals were anesthetized and euthanized. The livers obtained were excised, cut into 3- to 4-mm-thick slices and fixed in cold acetone at 4 °C. The liver specimens were then sliced into 25-µm-thick sections in PBS using an automated microtome (Vibratome 1500 Sectioning System, Vibratome Products, NY, USA). Immunocytochemical staining was performed in free solution, and the results were examined via digital light microscopy (Coolscope, Nikon, Tokyo).

RESULTS

3D analysis using a vibratome showed that GST-P is rapidly excreted into the bile of the liver of animals in response to strong carcinogenic stress caused by promoters or initiators. "Rapid biliary excretion of GST-P" was widely and commonly observed in all hepatocytes, GST-P+ single hepatocytes, minifoci, foci and nodules under appropriate conditions. Surprisingly, on the basis of these key findings, a new mechanism of cancer initiation involving the transformation of hepatocytes into GST-P+ single hepatocytes and minifoci in animal livers was identified. In addition, the initiation process was determined to be nongenetic because mutation is an invisible rare event.

CONCLUSIONS

This short review describes several details about breakthrough findings on cancer initiation in rat livers, the application of 3D analysis to other cancers and the importance in the genetic analysis in malignant diseases.

Biochemical analysis of the initial carcinogenic changes that induce preneoplastic and neoplastic cell populations during chemical hepatocarcinogenesis in rats

To analyze the initial carcinogenic changes that induce preneoplastic and neoplastic cell populations in the rat liver, a short-term in vivo promotion assay method was developed. Preneoplastic foci and nodules were quantitated with glutathione S-transferase P-form (GST-P) and γ-glutamyl transpeptidase. Among the four agents tested, benzyl isothiocyanate (BITC) demonstrated the strongest promotor activity, producing very large nodules composed of 2¹⁸ to 2²⁰ cells in the rat liver. In addition, a choline/methionine-deficient (CMD) diet, which strongly inhibits protein synthesis, exhibited lower but distinct promotive activity, giving rise to large nodules composed of 2¹¹ to 2¹³ cells. Based on the collected stereologic and biochemical data as well as the results of DNA microarray analysis, preneoplastic foci and nodules were strongly indicated to grow without cell division. The absence of cell division indicates the absence of mutations in the genetic mechanism, and vice versa; thus, preneoplastic cell induction can be considered nongenetic. Furthermore, the nodules were markedly more susceptible to promoter agents than hepatocytes as to die of necrosis. Based on these experimental findings, neoplastic cell induction was logically deduced to be nongenetic. The present analysis may help improve the knowledge of the "unknowable mechanism of cancer initiation" of rat chemical hepatocarcinogenesis.

Impact of Anesthetics, Analgesics, and Perioperative Blood Transfusion in Pediatric Cancer Patients: A Comprehensive Review of the Literature

Cancer is the leading cause of death by disease in developed countries. Children and adolescents with cancer need surgical interventions (ie, biopsy or major surgery) to diagnose, treat, or palliate their malignancies. Surgery is a period of high vulnerability because it stimulates the release of inflammatory mediators, catecholamines, and angiogenesis activators, which coincides with a period of immunosuppression. Thus, during and after surgery, dormant tumors or micrometastasis (ie, minimal residual disease) can grow and become clinically relevant metastasis. Anesthetics (ie, volatile agents, dexmedetomidine, and ketamine) and analgesics (ie, opioids) may also contribute to the growth of minimal residual disease or disease progression. For instance, volatile anesthetics have been implicated in immunosuppression and direct stimulation of cancer cell survival and proliferation. Contrarily, propofol has shown in vitro anticancer effects. In addition, perioperative blood transfusions are not uncommon in children undergoing cancer surgery. In adults, an association between perioperative blood transfusions and cancer progression has been described for some malignancies. Transfusion-related immunomodulation is one of the mechanisms by which blood transfusions can promote cancer progression. Other mechanisms include inflammation and the infusion of growth factors. In the present review, we discuss different aspects of tumorigenesis, metastasis, angiogenesis, the immune system, and the current studies about the impact of anesthetics, analgesics, and perioperative blood transfusions on pediatric cancer progression.

Asarone and metformin delays experimentally induced hepatocellular carcinoma in diabetic milieu

AIMS

The evidence suggests that the hyperglycemia and hyperinsulinemia of diabetes mellitus (DM) are risk factors for the development of hepatocellular carcinoma (HCC). The aim of the present study was to examine the effect of streptozotocin (STZ)-induced DM on promoting diethylnitrosamine (DEN) induced HCC in male wistar rats. Further, we investigated the administration of (α)-and (β)-asarone and metformin HCl on experimentally induced diabetic-hepatocellular carcinoma.

MATERIALS AND METHODS

Diabetes was induced by single dose of STZ (55 mg/2 ml/kg b.w. i.p.) and HCC by single dose of DEN (200 mg/ml/kg b.w. i.p.). Another group received the STZ followed by DEN two weeks later to mimic diabetic-HCC. The combined dose of (α)-and (β)-asarone (50 μg/1.5 ml/kg b.w. p.o. in the ratio of 1:1) and metformin HCl (250 mg/1.5 ml/kg b.w. p.o.) treatment was compared with the STZ + DEN group. The blood and liver samples were collected at the end of 12 and 18-weeks to study biochemical and histopathological changes in liver.

KEY FINDINGS

The STZ induced diabetes promoted the tumor progression due to administration of DEN. The treatment of asarones and metformin significantly reduced the levels of glucose, glycosylated hemoglobin, liver dysfunction markers and tumor biomarkers along with an increase in level of insulin when compared to diabetic-HCC group. Histopathological examination indicated that asarones and metformin attenuate the inflammation, fibrosis, cirrhosis and development of spontaneous HCC.

SIGNIFICANCE

The STZ can be used to promote the DEN induced HCC. Treatment with (α)-and (β)-asarone attenuates the effect of STZ + DEN induced HCC akin to metformin.

A mixture of Persistent Organic Pollutants (POPs) and Azoxymethane (AOM) show potential synergistic effects on intestinal tumorigenesis in the A/J Min/+ mouse model

A multitude of cancer types, including breast, testicular, liver and colorectal cancer, have associations with exposure to Persistent Organic Pollutants (POPs). The present study aimed to investigate whether a mixture of POPs could affect intestinal tumorigenesis in the A/J Min/+ mouse, a model for human colorectal cancer (CRC). Pollutants were selected for their presence in Scandinavian food products and the mixture was designed based on defined human estimated daily intake levels. Mice were exposed through the diet, at control, low and high mixture concentrations, for 10 weeks. In a separate experiment, mice also received one subcutaneous injection of Azoxymethane (AOM) to explore whether this carcinogenic compound influenced the effect of the POPs. Intestinal tumorigenesis was examined by surface microscopy and histopathology. Moderate and dose-dependent increases in tumorigenesis were observed after dietary POP exposure. The AOM treatment alone stimulated the growth of colonic lesions, but did not increase the formation of new lesions. Combined AOM treatment and POP exposure demonstrated a synergistic effect on lesion formation in the colon, and to a lesser extent in the small intestine. This synergy was also evident by an increased number of malignant colonic tumors (carcinomas). In conclusion, the study shows that a mixture of POPs interacted synergistically with a known carcinogen (AOM), causing increased intestinal tumorigenesis in the A/J Min/+ mouse model.

Development versus Evolution in Cancer Biology

The terms 'development' and 'evolution' are both used to describe the unfolding of the carcinogenic process. However, there is increasing awareness of an essential difference in the meanings of these two terms with reference to cancer. We discuss evidence suggesting that the concepts of development and evolution are both pertinent to the description of carcinogenesis; however, they appropriately apply to distinct phases of a multistep process. Such a distinction bears important implications for the study and management of cancer.

Evolution of indeterminate hepatocellular nodules at Gd-EOB-DPTA-enhanced MRI in cirrhotic patients

PURPOSE

To retrospectively analyze the evolution of indeterminate hepatocellular nodules in cirrhotic patients on serial Gd-EOB-DPTA-enhanced MRI, and to identify predictors of HCC development.

MATERIALS AND METHODS

This IRB approved study included 33 cirrhotic patients with 69 indeterminate hepatocellular nodules (mean diameter 1.1 cm) at baseline Gd-EOB-DPTA-enhanced MRI and a Gd-EOB-DPTA-enhanced-MRI follow-up of at least 2 years. Two radiologists evaluated size and signal intensity of each nodule at baseline and follow-up. Age, cirrhosis etiology, and HCC history were recorded. Data were compared between nodules that became HCCs at follow-up (HCC) and those that did not (no-HCC).

RESULTS

On follow-up, 5/69 nodules became HCCs and 64/69 showed indeterminate characteristics. HCC history was more frequently found in HCCs than in no-HCCs. Age, sex, and cirrhosis etiology were not significantly different between HCCs and no-HCCs. HCCs had a significantly greater baseline diameter and increase in size than no-HCCs. Hepatobiliary phase hypointensity was significantly more common in HCCs than in no-HCCs. Multivariate regression analysis showed that increase in size (OR 10.48; sensitivity, 100%; specificity, 81.2%; p < 0.001) and hepatobiliary phase hypointensity (OR 1.02; sensitivity, 100%; specificity, 78.1%; p < 0.001) was associated with HCC development.

CONCLUSION

Indeterminate hepatocellular nodules at Gd-EOB-DPTA-enhanced MRI in cirrhotic patients rarely became HCCs. Hepatobiliary phase hypointensity had a weak association with HCC development.

The Use of In vivo Hepatic Initiation-Promotion Systems in Understanding the Hepatocarcinogenesis of Technical Grade Dinitrotoluene

A 2 year bioassay sponsored by the Chemical Industry Institute of Toxicology demonstrated the potent hepatocarcinogenicity of technical grade dinitrotoluene (DNT) which contains 76% 2,4-DNT, 18% 2,6-DNT and less than 3% of each 2,3; 2,5; 3,4 and 3,5-DNT isomers. In contrast, a 2 year bioassay of 2,4-DNT sponsored by the National Cancer Institute did not result in the appearance of hepatic neoplasms above the spontaneous incidence. Using previously described in vivo hepatic initiation-promotion systems, an evaluation of the initiating and promoting activity of individual DNT isomers was undertaken to provide an understanding for the differences between the two bioassays. Weak hepatocyte initiating activity was identified in technical grade DNT and purified 2,6-DNT. In contrast, 2,3; 2,4; 2,5; 3,4 and 3,5 isomers had no detectable initiating activity. When fed following a diethylnitrosamine initiating regimen, technical grade DNT, purified 2,4 and 2,6-DNT isomers had demonstrable promoting activity. Therefore, the hepatic neoplasms resulting from technical grade DNT feeding apparently resulted from the initiating activity of 2,6-DNT followed by the promoting effect of both the 2,4 and 2,6-DNT isomers. The lack of hepatic neoplasms following chronic feeding of 2,4-DNT was apparently due to the lack of hepatic initiating activity.

The Biology of Carcinogen-Induced Hepatocyte Nodules and Related Liver Lesions in the Rats

The only known sequence of tissue changes seen during liver cancer development involves microscopic foci or islands of altered hepatocytes, hepatocyte nodules, a subset of these nodules, the persistent nodules, nodules in nodules and ultimately hepatocellular carcinoma. The nodules show an array of architectural, fine ultrastructural, vascular, biochemical and physiological properties characteristic of this new population of hepatocytes. Despite their origin following initiation with a chemical carcinogen, the vast majority (98-99%) of nodules undergo a complex process of remodeling or redifferentiation to normal looking mature liver. A very small minority persist, continue to grow slowly and ultimately may act as a site of origin for new later precancerous nodules and metastasizing hepatocellular carcinoma. The basis for the different behaviour patterns, remodelling of the majority and persistence of the minority is not understood. Even though the vast majority of nodules do undergo remodelling and “disappear”, it would be unwise at this time to ignore this key role of nodules in general in cancer development.

Hypolipidemics Carcinogenicity and Extrapolation of Experimental Results for Human Safety Assessments

Dyslipoproteinemias represent a group of disorders closely related to alterations of cholesterol and triglycerides. The alterations of these lipids are considered important risk factors in coronary heart disease and indicate the need for clinically effective and safe drugs.

Hypolipidemic agent therapy, however, does not appear without risk since the administration of these agents is by necessity, on a long-term basis. In the conduct of animal safety studies with some hypolipidemics, hyperplastic nodules or tumors developed in the liver of rodents. Data from the literature seem to indicate that the tumor response in rodents varies with the type of hypolipidemic drug administered. This paper summarizes the studies with the new lipid-regulating agent gemfibrozil. Aside from conventional long-term studies in rodents, the ultrastructural aspects of the liver were analyzed in several species and genotoxicity assays and short-term tests for hepatocarcinogenicity were conducted. Thus, it was possible to obtain an overview of these biological phenomena in order to allow for safety extrapolations. The biological behavior of these liver nodules showed that gemfibrozil and clofibrate-induced hepatocytes had not undergone malignant transformation. Further, the phenomenon of peroxisome proliferation, a characteristic event that follows hypolipidemic administration in rodents, was not confirmed in primate or human liver. Peroxisome proliferation has been linked to the process of hepatocarcinogenesis in rodents, although genotoxicity assays were negative and initiation/promotion tests failed to elicit tumors or nodules in a system where hepatocarcinogens manifest their activity.

Thus, hypolipidemics such as gemfibrozil or Clofibrate may possess low tumorigenic potential with low risk due to the lack of correlation between these tests. Nevertheless, these agents are indicated for specific lipoprotein phenotype alteration with the resulting clinical benefits.

The Use of In vivo Hepatic Initiation-Promotion Systems in Understanding the Hepatocarcinogenesis of Technical Grade Dinitrotoluene

A 2 year bioassay sponsored by the Chemical Industry Institute of Toxicology demonstrated the potent hepatocarcinogenicity of technical grade dinitrotoluene (DNT) which contains 76% 2,4-DNT, 18% 2,6-DNT and less than 3% of each 2,3; 2,5; 3,4 and 3,5-DNT isomers. In contrast, a 2 year bioassay of 2,4-DNT sponsored by the National Cancer Institute did not result in the appearance of hepatic neoplasms above the spontaneous incidence. Using previously described in vivo hepatic initiation-promotion systems, an evaluation of the initiating and promoting activity of individual DNT isomers was undertaken to provide an understanding for the differences between the two bioassays. Weak hepatocyte initiating activity was identified in technical grade DNT and purified 2,6-DNT. In contrast, 2,3; 2,4; 2,5; 3,4 and 3,5 isomers had no detectable initiating activity. When fed following a diethylnitrosamine initiating regimen, technical grade DNT, purified 2,4 and 2,6-DNT isomers had demonstrable promoting activity. Therefore, the hepatic neoplasms resulting from technical grade DNT feeding apparently resulted from the initiating activity of 2,6-DNT followed by the promoting effect of both the 2,4 and 2,6-DNT isomers. The lack of hepatic neoplasms following chronic feeding of 2,4-DNT was apparently due to the lack of hepatic initiating activity.

Liver Tumor Induction

The significance of the development of nodular liver lesions in rodents following the administration of test agents raises several questions which could be placed in one of two general categories: diagnostic and interpretational. From a diagnostic point of view, the proper classification of liver tumors into a benign and malignant category has to be based on the direct correlation between the morphology and the biologic behavior of the lesions. Therefore, extreme care should be taken to separate the malignant tumors from the benign and the benign neoplasia from the hyperplasia. The substitution of the term “neoplastic nodule” for hyperplastic nodule in rats is misleading. Most of these nodules, when induced under special experimental conditions, may regress or remodel and thus they are not neoplastic in nature. Chronic carcinogenicity bioassays should include “stop” type of treatment leaving enough of the observational time to establish the fate of induced nodular lesions. The induction of histochemically changed foci can serve only as an indication of potential hepatocarcinogenicity and should not be equated with the induction of bona fide cancer. The biologic interpretation of nodular liver lesions, especially in mice, needs further scrutiny because these lesions have a tendency to develop spontaneously with high incidence in some strains. This characteristic then raises the question as to the mechanism by which various agents augment and/or accelerate the development of such tumors. Is this action primarily promoting or initiating in nature or does it represent the induction of tumors de novo? The answer to this dilemma may have a decisive bearing on carcinogenic risk assessment and the type of regulatory action, since the promoting agents possess a threshold effect and the promoted changes may regress following withdrawal of treatment. The interpretation of hepatocarcinogenesis is further complicated by the fact that several factors, such as sex hormonal environment, increased mitotic activity following an excessive loss of parenchymal cells, degree of caloric intake, enzymatic complement, and animals’ age at the time of the exposure to a test agent, may influence the outcome of liver tumor development by modulating “initiation” and/or “promotion” of carcinogenesis. Broad fluctuation in the historic incidence of liver tumors further compounds the complexity of the proper bioassay interpretation. The specifically designed experiments may have the objective to explore predominantly the initiating or promoting effects of the agent. Such protocols should be used whenever necessary to differentiate between these two mechanisms of action. In the Caucasians, the “spontaneous” development of the primary hepatocellular tumors is rare. The majority of these tumors are malignant and rapidly fatal. According to some human pathologists, the benign variety of liver tumors is rare and it does not represent necessarily a premalignant stage in tumor development. Carcinoma of the liver may occur in infancy, especially in males before the age of 2 years. This suggests a genetic causation or carcinogenic exposure in utero. One of the geographic factors which significantly enhances the incidence of hepatocellular carcinoma in humans is exposure to aflatoxin B1 which is apparently potentiated by concurrent liver cirrhosis. Because many more agents have been found to be hepatocarcinogenic in mice and rats than in men, a question arises as to the direct relevance of rodent studies to humans. A balanced assessment of the carcinogenicity of the agent could only be reached in considering both the pharmacokinetics and the development of malignant neoplasia in other organs. In the case of positive carcinogenicity assessment, the outcome of the mutagenicity bioassays can suggest genic (genotoxic) or paragenic (epigenetic) mode of action in mammalian systems.

Hypolipidemics Carcinogenicity and Extrapolation of Experimental Results for Human Safety Assessments

Dyslipoproteinemias represent a group of disorders closely related to alterations of cholesterol and triglycerides. The alterations of these lipids are considered important risk factors in coronary heart disease and indicate the need for clinically effective and safe drugs.

Hypolipidemic agent therapy, however, does not appear without risk since the administration of these agents is by necessity, on a long-term basis. In the conduct of animal safety studies with some hypolipidemics, hyperplastic nodules or tumors developed in the liver of rodents. Data from the literature seem to indicate that the tumor response in rodents varies with the type of hypolipidemic drug administered. This paper summarizes the studies with the new lipid-regulating agent gemfibrozil. Aside from conventional long-term studies in rodents, the ultrastructural aspects of the liver were analyzed in several species and genotoxicity assays and short-term tests for hepatocarcinogenicity were conducted. Thus, it was possible to obtain an overview of these biological phenomena in order to allow for safety extrapolations. The biological behavior of these liver nodules showed that gemfibrozil and clofibrate-induced hepatocytes had not undergone malignant transformation. Further, the phenomenon of peroxisome proliferation, a characteristic event that follows hypolipidemic administration in rodents, was not confirmed in primate or human liver. Peroxisome proliferation has been linked to the process of hepatocarcinogenesis in rodents, although genotoxicity assays were negative and initiation/promotion tests failed to elicit tumors or nodules in a system where hepatocarcinogens manifest their activity.

Thus, hypolipidemics such as gemfibrozil or clofibrate may possess low tumorigenic potential with low risk due to the lack of correlation between these tests. Nevertheless, these agents are indicated for specific lipoprotein phenotype alteration with the resulting clinical benefits.

Multi-step lung carcinogenesis model induced by oral administration of N-nitrosobis(2-hydroxypropyl)amine in rats

N-Nitrosobis(2-hydroxypropyl)amine (BHP) was first synthesized by Krüger et al. (1974), and has been shown to primarily induce pancreatic duct adenocarcinomas by a subcutaneous injection in Syrian hamsters. By contrast, the carcinogenic effect of BHP has been indicated at the different target organs in rats, namely the lung. When rats are received by an oral administration of BHP in drinking water for 25 weeks, a high incidence of lung carcinomas are induced, which include adenocarcinomas, squamous cell carcinomas and combined squamous cell and adenocarcinomas. So many similarities are observed in terms of not only histological appearances but also gene alterations between human and BHP-induced rat lung cancers. Moreover, the step by step development of lung lesions, from preneoplastic lesions to cancers in rat lung carcinogenesis by BHP offers a good model to investigate the mechanisms underlying the pathogenesis of lung cancers. Because data for genetic and epigenetic alterations have indeed been accumulated during the BHP-induced rat lung carcinogenesis, we will introduce them in this review and hence demonstrate that this lung carcinogenesis model provides a useful opportunity for the research on the pathogenesis of lung cancers of both humans and rats.

Zinc and zinc related enzymes in precancerous and cancerous tissue in the colon of dimethyl hydrazine treated rats

Trace element zinc deficiency or excess is implicated in the development or progression of some cancers. The exact role of zinc in the etiology of colon cancer is unclear. To cast light on this question, an experimental model of colon carcinogenesis was applied here. Six week old rats were given sub cutaneous injections of DMH (30 mg/kg body weight) twice a week for three months and sacrificed after 4 months (precancer model) and 6 months (cancer model). Plasma zinc levels showed a significant decrease (p<0.05) at 4 months and a greater significant decrease at 6 months (p<0.01) as compared with controls. In the large intestine there was a significant decrease in tissue zinc levels (p<0.005) and in CuZnSOD, and alkaline phosphatase activity (p<0.05) in the pre-cancerous model and a greater significant decrease in tissue zinc (p<0.0001), and in CuZnSOD and alkaline phosphatase activity (p<0.001), in the carcinoma model. The tissue zinc levels showed a significant decrease in the small intestine and stomach (p<0.005) and in liver (p<0.05) in the cancer model. 87% of the rats in the precancer group and 92% rats in the cancer group showed histological evidence of precancerous lesions and carcinomas respectively in the colon mucosa. This study suggests that the decrease in plasma zinc, tissue zinc and activity of zinc related enzymes are associated with the development of preneoplastic lesions and these biochemical parameters further decrease with progression to carcinoma in the colon.

Nonclonal growth of preneoplastic cells positive for glutathione S-transferase P-form in the rat liver

We investigated the process of induction of preneoplastic cells positive for glutathione S-transferase P-form (GST-P) in the rat liver. AAF (2-Acetylaminofluorene) mixed with normal rat chow at high concentration (0.04%) induced 517 000 ± 86,000 GST-P(+) single hepatocytes/g liver after 2 weeks followed by induction of a few foci and nodules after 4-6 weeks. Overproduction of GST-P(+) single hepatocytes was dose- and time-dependent, and the induction kinetics were typical of first-order consecutive reaction, by which induction of the positive cells was nongenetic. Quantitative analysis indicated that the estimated numbers of cells in foci and nodules at 4-6 weeks after exposure to AAF ranged from 2.7 × 10(4) (2(14.7)) to 3.6 × 10(6) (2(21.7)) cells, and 2.0 × 10(4) (2(14.3)) to 2.7 × 10(6) (2(21.4)) cells, respectively, when analyzed by using two equations. According to the initiated cell theory of Farber, foci and nodules are formed through sequential cell division of 14 to 21-times or more within a short time period. The rapid growth exceeded the rate of cell division, indicating that the growth of preneoplastic cells is based on a nonclonal penetration mechanism.

Tumor heterogeneity: mechanisms and bases for a reliable application of molecular marker design

Tumor heterogeneity is a confusing finding in the assessment of neoplasms, potentially resulting in inaccurate diagnostic, prognostic and predictive tests. This tumor heterogeneity is not always a random and unpredictable phenomenon, whose knowledge helps designing better tests. The biologic reasons for this intratumoral heterogeneity would then be important to understand both the natural history of neoplasms and the selection of test samples for reliable analysis. The main factors contributing to intratumoral heterogeneity inducing gene abnormalities or modifying its expression include: the gradient ischemic level within neoplasms, the action of tumor microenvironment (bidirectional interaction between tumor cells and stroma), mechanisms of intercellular transference of genetic information (exosomes), and differential mechanisms of sequence-independent modifications of genetic material and proteins. The intratumoral heterogeneity is at the origin of tumor progression and it is also the byproduct of the selection process during progression. Any analysis of heterogeneity mechanisms must be integrated within the process of segregation of genetic changes in tumor cells during the clonal expansion and progression of neoplasms. The evaluation of these mechanisms must also consider the redundancy and pleiotropism of molecular pathways, for which appropriate surrogate markers would support the presence or not of heterogeneous genetics and the main mechanisms responsible. This knowledge would constitute a solid scientific background for future therapeutic planning.

Comfrey (Symphytum Officinale. l.) and Experimental Hepatic Carcinogenesis: A Short-term Carcinogenesis Model Study

Comfrey or Symphytum officinale (L.) (Boraginaceae) is a very popular plant used for therapeutic purposes. Since the 1980s, its effects have been studied in long-term carcinogenesis studies, in which Comfrey extract is administered at high doses during several months and the neoplastic hepatic lesions are evaluated. However, the literature on this topic is very poor considering the studies performed under short-term carcinogenesis protocols, such as the 'resistant hepatocyte model' (RHM). In these studies, it is possible to observe easily the phenomena related to the early phases of tumor development, since pre-neoplastic lesions (PNLs) rise in about 1-2 months of chemical induction. Herein, the effects of chronic oral treatment of rats with 10% Comfrey ethanolic extract were evaluated in a RHM. Wistar rats were sequentially treated with N-nitrosodiethylamine (ip) and 2-acetilaminofluorene (po), and submitted to hepatectomy to induce carcinogenesis promotion. Macroscopic/microscopic quantitative analysis of PNL was performed. Non-parametric statistical tests (Mann-Whitney and χ(2)) were used, and the level of significance was set at P ≤ 0.05. Comfrey treatment reduced the number of pre-neoplastic macroscopic lesions up to 1 mm (P ≤ 0.05), the percentage of oval cells (P = 0.0001) and mitotic figures (P = 0.007), as well as the number of Proliferating Cell Nuclear Antigen (PCNA) positive cells (P = 0.0001) and acidophilic pre-neoplastic nodules (P = 0.05). On the other hand, the percentage of cells presenting megalocytosis (P = 0.0001) and vacuolar degeneration (P = 0.0001) was increased. Scores of fibrosis, glycogen stores and the number of nucleolus organizing regions were not altered. The study indicated that oral treatment of rats with 10% Comfrey alcoholic extract reduced cell proliferation in this model.

Bile duct-bound growth of precursor cells of preneoplastic foci inducible in the initiation stage of rat chemical hepatocarcinogenesis by 2-acetylaminofluorene

BACKGROUND

We previously detected precursor cell populations of preneoplastic foci, GST-P(+)/GGT(-) and GST-P(+)/GGT(+) minifoci, in rat liver in the initiation stage of chemical hepatocarcinogenesis, where GST-P and GGT represent glutathione S-transferase P-form and gamma-glutamyltranspeptidase, respectively.

METHODS

Sprague-Dawley male rats were fed a basal diet containing 2-acetylaminofluorene (0.02%) over 16 weeks. Precursor cells were detected by our sensitive staining method for GGT activity and immunocytochemical staining for GST-P.

RESULTS

GST-P(+)/GGT(-) single cells were overproduced maximally in the animal liver after the 6 weeks followed by a gradual growth of GST-P(+)/GGT(-) and GST-P(+)/GGT(+) minifoci, which were bound to bile ducts and ductules. GGT was expressed within GST-P(+) minifoci gradually with time forming GGT(+) lane-like structures. The bile duct binding and lane-like structure formation were prominent especially when minifoci-bearing rats were subjected to two-thirds partial hepatectomy.

CONCLUSIONS

A variety of precursor minifoci were noted to be selectively bound to bile ducts and ductules in rat liver, which may be of physiologic significance in excretion of carcinogens during initiation.

An adjustment factor for mode-of-action uncertainty with dual-mode carcinogens: the case of naphthalene-induced nasal tumors in rats

The U.S. Environmental Protection Agency (USEPA) guidelines for cancer risk assessment recognize that some chemical carcinogens may have a site-specific mode of action (MOA) involving mutation and cell-killing-induced hyperplasia. The guidelines recommend that for such dual MOA (DMOA) carcinogens, judgment should be used to compare and assess results using separate "linear" (genotoxic) versus "nonlinear" (nongenotoxic) approaches to low-level risk extrapolation. Because the guidelines allow this only when evidence supports reliable risk extrapolation using a validated mechanistic model, they effectively prevent addressing MOA uncertainty when data do not fully validate such a model but otherwise clearly support a DMOA. An adjustment-factor approach is proposed to address this gap, analogous to reference-dose procedures used for classic toxicity endpoints. By this method, even when a "nonlinear" toxicokinetic model cannot be fully validated, the effect of DMOA uncertainty on low-dose risk can be addressed. Application of the proposed approach was illustrated for the case of risk extrapolation from bioassay data on rat nasal tumors induced by chronic lifetime exposure to naphthalene. Bioassay data, toxicokinetic data, and pharmacokinetic analyses were determined to indicate that naphthalene is almost certainly a DMOA carcinogen. Plausibility bounds on rat-tumor-type-specific DMOA-related uncertainty were obtained using a mechanistic two-stage cancer risk model adapted to reflect the empirical link between genotoxic and cytotoxic effects of the most potent identified genotoxic naphthalene metabolites, 1,2- and 1,4-naphthoquinone. Bound-specific adjustment factors were then used to reduce naphthalene risk estimated by linear extrapolation (under the default genotoxic MOA assumption), to account for the DMOA exhibited by this compound.

Alpha-fetoprotein, stem cells and cancer: how study of the production of alpha-fetoprotein during chemical hepatocarcinogenesis led to reaffirmation of the stem cell theory of cancer

Identification of the cells in the liver that produce alpha-fetoprotein during development, in response to liver injury and during the early stages of chemical hepatocarcinogenesis led to the conclusion that maturation arrest of liver-determined tissue stem cells was the cellular process that gives rise to hepatocellular carcinomas. When the cellular changes in these processes were compared to that of the formation of teratocarcinomas, the hypothesis arose that all cancers arise from maturation arrest of tissue-determined stem cells. This was essentially a reinterpretation of the embryonal rest theory of cancer whereby tissue stem cells take the role of embryonal rests. A corollary of the stem cell theory of the origin of cancer is that cancers contain the same functional cell populations as normal tissues: stem cells, transit-amplifying cells and mature cells. Cancer stem cells retain the essential feature of normal stem cells: the ability to self-renew. Growth of cancers is due to continued proliferation of cancer transit-amplifying cells that do not differentiate to mature cells (maturation arrest). On the other hand, cancer stem cells generally divide very rarely and contribute little to tumor growth. However, the presence of cancer stem cells in tumors is believed to be responsible for the properties of immortalization, transplantability and resistance to therapy characteristic of cancers. Current therapies for cancer (chemotherapy, radiotherapy, antiangiogenesis and differentiation therapy) are directed against the cancer transit-amplifying cells. When these therapies are discontinued, the cancer reforms from the cancer stem cells. Therapy directed toward interruption of the cell signaling pathways that maintain cancer stem cells could lead to new modalities to the prevention of regrowth of the cancer.

Naphthalene metabolism in relation to target tissue anatomy, physiology, cytotoxicity and tumorigenic mechanism of action

This report provides a summary of deliberations conducted under the charge for members of Module C Panel participating in the Naphthalene State-of-the-Science Symposium (NS(3)), Monterey, CA, October 9-12, 2006. The panel was charged with reviewing the current state of knowledge and uncertainty about naphthalene metabolism in relation to anatomy, physiology and cytotoxicity in tissues observed to have elevated tumor incidence in these rodent bioassays. Major conclusions reached concerning scientific claims of high confidence were that: (1) rat nasal tumor occurrence was greatly enhanced, if not enabled, by adjacent, histologically related focal cellular proliferation; (2) elevated incidence of mouse lung tumors occurred at a concentration (30 ppm) cytotoxic to the same lung region at which tumors occurred, but not at a lower and less cytotoxic concentration (tumorigenesis NOAEL=10 ppm); (3) naphthalene cytotoxicity requires metabolic activation (unmetabolized naphthalene is not a proximate cause of observed toxicity or tumors); (4) there are clear regional and species differences in naphthalene bioactivation; and (5) target tissue anatomy and physiology is sufficiently well understood for rodents, non-human primates and humans to parameterize species-specific physiologically based pharmacokinetic (PBPK) models for nasal and lung effects. Critical areas of uncertainty requiring resolution to enable improved human cancer risk assessment were considered to be that: (1) cytotoxic naphthalene metabolites, their modes of cytotoxic action, and detailed low-dose dose-response need to be clarified, including in primate and human tissues, and neonatal tissues; (2) mouse, rat, and monkey inhalation studies are needed to better define in vivo naphthalene uptake and metabolism in the upper respiratory tract; (3) in vivo validation studies are needed for a PBPK model for monkeys exposed to naphthalene by inhalation, coupled to cytotoxicity studies referred to above; and (4) in vivo studies are needed to validate a human PBPK model for naphthalene. To address these uncertainties, the Panel proposed specific research studies that should be feasible to complete relatively promptly. Concerning residual uncertainty far less easy to resolve, the Panel concluded that environmental, non-cytotoxic exposure levels of naphthalene do not induce tumors at rates that can be predicted meaningfully by simple linear extrapolation from those observed in rodents chronically exposed to far greater, cytotoxic naphthalene concentrations.

Toxicological significance of liver hypertrophy produced by inducers of drug-metabolizing enzymes

Changes in enzyme activity due to induction by chemicals is an important property that can determine the type of response seen in tissues exposed to environmental chemicals. Two major types of response, acute irreversible liver cell injury or death (necrosis) and long-term cancer induction, are discussed in terms of their modulation by enzyme induction. Most commonly, enzyme induction leads to a more severe toxic response by the liver, and to more cell death. However, inducers may have a protective effect, especially in carcinogenesis, when they most frequently protect against cancer induction if used early in the process. There is a discrepancy between this observation and the increase in mutagenic activity of liver preparations observed after induction. However, when enzyme induction occurs at a later stage, after initiation, it often accelerates or promotes cancer induction. Also, new cell populations constantly observed during liver carcinogenesis are composed of very hypertrophic hepatocytes containing a large amount of smooth endoplasmic reticulum. This is associated with a radical change in enzyme activities in the reticulum, which may account in part for the characteristic resistance exhibited by initiated cells to hepatotoxins and carcinogens. The resistance is considered to be an important property that may play a key role in the development of cancer under some circumstances.

The microenvironments of multistage carcinogenesis

Overt neoplasia is often the result of a chronic disease process encompassing an extended segment of the lifespan of any species. A common pathway in the natural history of the disease is the appearance of focal proliferative lesions that are known to act as precursors for cancer development. It is becoming increasingly apparent that the emergence of such lesions is not a cell-autonomous phenomenon, but is heavily dependent on microenvironmental cues derived from the surrounding tissue. Specific alterations in the tissue microenvironment that can foster the selective growth of focal lesions are discussed herein. Furthermore, we argue that a fundamental property of focal lesions as it relates to their precancerous nature lies in their altered growth pattern as compared to the tissue where they reside. The resulting altered tissue architecture translates into the emergence of a unique tumor microenvironment inside these lesions, associated with altered blood vessels and/or blood supply which in turn can trigger biochemical and metabolic changes fueling tumor progression. A deeper understanding of the role(s) of tissue and tumor microenvironments in the pathogenesis of cancer is essential to design more effective strategies for the management of this disease.

Suppression of early stages of neoplastic transformation in a two-stage chemical hepatocarcinogenesis model: supplementation of vanadium, a dietary micronutrient, limits cell proliferation and inhibits the formations of 8-hydroxy-2'-deoxyguanosines and DNA strand-breaks in the liver of sprague-dawley rats

Previous studies from our laboratory have demonstrated the potential anticarcinogenicity of vanadium, a dietary micronutrient in rat liver, colon, and mammary carcinogenesis models in vivo. In this paper, we have investigated further the antihepatocarcinogenic role of this essential trace element by studying several biomarkers of chemical carcinogenesis with special reference to cell proliferation and oxidative DNA damage. Hepatocarcinogenesis was induced in male Sprague-Dawley rats by chronic feeding of 2-acetylaminofluorene (2-AAF) at a dose of 0.05% in basal diet daily for 5 days a week. Vanadium in the form of ammonium metavanadate (0.5 ppm equivalent to 4.27 micromol/l) was supplemented ad lib to the rats. Continuous vanadium administration reduced relative liver weight, nodular incidence (79.99%), total number and multiplicity (P < 0.001; 68.17%) along with improvement in hepatocellular architecture when compared to carcinogen control. Vanadium treatment further restored hepatic uridine diphosphate (UDP)-glucuronosyl transferase and UDP-glucose dehydrogenase activities, inhibited lipid peroxidation, and prevented the development of glycogen-storage preneoplastic foci (P < 0.01; 63.29%) in an initiation-promotion model. Long-term vanadium treatment also reduced BrdU-labelling index (P < 0.02) and inhibited cell proliferation during hepatocellular preneoplasia. Finally, short-term vanadium exposure abated the formations of 8-hydroxy-2'-deoxyguanosines (P < 0.001; 56.27%), length:width of DNA mass (P < 0.01), and the mean frequency of tailed DNA (P < 0.001) in preneoplastic rat liver. The study indicates the potential role of vanadium in suppressing cell proliferation and in preventing early DNA damage in vivo. Vanadium is chemopreventive against the early stages of 2-AAF-induced hepatocarcinogenesis in rats.

Molecular basis of vanadium-mediated inhibition of hepatocellular preneoplasia during experimental hepatocarcinogenesis in rats

Carcinogen-induced early DNA lesions and metallothionein (MT) over-expression have been implicated in cell proliferation and thereby subsequent expression of premalignant phenotype of the cell. We have therefore investigated the chemopreventive potential of vanadium in a multi-biomarker approach, viz. 8-hydroxy-2'-deoxyguanosines (8-OHdGs), DNA single-strand breaks (SSBs), DNA-protein crosslinks (DPCs), chromosomal aberrations (CAs), in situ MT expression, and cell proliferation in rat liver preneoplasia. Hepatocarcinogenesis was induced in male Sprague-Dawley rats with a single, necrogenic, intraperitoneal (i.p.) injection of diethylnitrosamine (DEN) (200 mg/Kg body weight) at week 4 of the experimental protocol followed by promotion with phenobarbital (PB) (0.05% in basal diet), on and from week 8 and continued till 32 weeks in a long-term regimen. There was a significant and steady elevation of modified DNA bases 8-OHdGs (P < 0.0001; 90.69%) along with substantial increments of the extent of SSBs (P < 0.001) and CAs (P < 0.001) following DEN exposure. Supplementation of vanadium at a dose of 0.5 ppm abated the formations of 8-OHdGs (80.63%; P < 0.0001), SS-DNAs (P < 0.001) and SSBs/DNA unit (P < 0.01; 56.39%), DPCs (59.26%; P < 0.0001) and CAs (71.52%; P < 0.001) in preneoplastic rat liver studied at various time points. Low dose of vanadium treatment further reduced liver-MT immunoreactivity (P < 0.05) and BrdU-labeling index (P < 0.02) and a significant positive correlation (r = 0.92; r2 = 0.85; P = 0.0001) was noted between them. Continuous vanadium administration also decreased nodular incidence (66.67%) and nodule multiplicity (62.12%; P < 0.001) along with substantial improvement in the altered hepatocellular phenotype when compared to DEN + PB treatment alone. The study indicates that vanadium-mediated suppression of cell proliferation and resulting premalignant expression might be due to the observed reductions in hepatic 8-OHdGs, SSBs, DPCs, CAs, and MT immunoreactivity. Vanadium is chemopreventive for DEN-induced hepatocellular preneoplasia in rats.

Carcinogen-induced early molecular events and its implication in the initiation of chemical hepatocarcinogenesis in rats: Chemopreventive role of vanadium on this process

Carcinogen-induced formation of DNA adducts and other types of DNA lesions are the critical molecular events in the initiation of chemical carcinogenesis and modulation of such events by chemopreventive agents could be an important step in limiting neoplastic transformation in vivo. Vanadium, a dietary micronutrient has been found to be effective in several types of cancers both in vivo and in vitro and also possesses profound anticarcinogenicity against rat models of mammary, colon and hepatocarcinogenesis. Presently, we report the chemopreventive potential of vanadium on diethylnitrosamine (DEN)-induced early DNA damages in rat liver. Hepatocarcinogenesis was induced in male Sprague-Dawley rats with a single, necrogenic, intraperitoneal (i.p.) injection of DEN (200 mg/kg body weight) at week 4. There was a significant induction of tissue-specific ethylguanines, steady elevation of modified DNA bases 8-hydroxy-2'-deoxyguanosines (8-OHdGs) (P<0.0001; 89.93%) along with substantial increment of the extent of single-strand breaks (SSBs) (P<0.0001) following DEN exposure. Supplementation of 0.5 ppm of vanadium throughout the experiment abated the formations of O(6)-ethylguanines and 7-ethylguanines (P<0.0001; 48.71% and 67.54% respectively), 8-OHdGs (P<0.0001; 81.37%), length:width (L:W) of DNA mass (P<0.01; 62.12%) and the mean frequency of tailed DNA (P<0.001; 53.58%), and hepatic nodulogenesis in preneoplastic rat liver. The study indicates that 0.5 ppm vanadium is potentially and optimally effective, as derived from dose-response studies, in limiting early molecular events and preneoplastic lesions, thereby modulating the initiation stage of hepatocarcinogenesis. Vanadium is chemopreventive against DEN-induced genotoxicity and resulting hepatocellular transformation in rats.

Vanadium limits the expression of proliferating cell nuclear antigen and inhibits early DNA damage during diethylnitrosamine-induced hepatocellular preneoplasia in rats

Previous studies from our laboratory have shown that vanadium stabilizes xenobiotic metabolizing enzymes and antioxidant status and suppresses DNA-protein crosslinks during chemically-induced hepatocarcinogenesis in rats. In the present study, we have further investigated the in vivo antitumor potential of this micronutrient by determining the effect of 0.5 ppm vanadium in drinking water on biomarkers for the early stages of hepatocarcinogenesis; the biomarkers included gamma-glutamyl transpeptidase (GGT)-positive foci and glycogen-storage foci, in situ expression of proliferating cell nuclear antigen (PCNA), and genotoxic DNA damage assessed by the alkaline Comet assay. Histomorphometry also was assessed during the study. Hepatocarcinogenesis was induced by treating 4-week-old male Sprague-Dawley rats with a single, necrogenic, intraperitoneal (i.p.) injection of 200 mg/kg body weight diethylnitrosamine (DEN). Compared to the carcinogen control, vanadium administration over the 32 weeks of the experiment reduced the relative liver weight by 30%, the incidence of nodules by 69.34%, the total number and multiplicity of nodules by 80.77%, and remodeled the hepatocellular premalignant architecture towards a normal phenotype. Moreover, long-term vanadium treatment reduced the development of GGT foci by 76.2% (P < 0.001), decreased periodic acid-Schiff's reactivity by 59.49% (P < 0.01), and decreased PCNA expression, with the concomitant reduction in PCNA immunolabeling index by 93.36% (P < 0.001). Finally, vanadium inhibited early DNA damage (DNA strand-breaks) in DEN-treated rat hepatocytes as expressed in the Comet assay by a 60.04% reduction in the length:width value of DNA mass (P < 0.01) and a 51.54% reduction in the tail length of the DNA comets (P < 0.001). Our results indicate that continuous supplementation with 0.5 ppm vanadium suppresses hepatocellular neoplastic transformation in rats.

Chemopreventive effect of vanadium in a rodent model of chemical hepatocarcinogenesis: reflections in oxidative DNA damage, energy-dispersive X-ray fluorescence profile and metallothionein expression

In the present study, we investigated the antitumour efficacy of vanadium in a defined rodent model of experimental hepatocarcinogenesis. Hepatic preneoplasia was induced in male Sprague-Dawley rats with a single, necrogenic, intraperitoneal injection of diethylnitrosamine (DEN) (200 mg/kg body weight) followed by promotion with phenobarbital (PB). The levels of modified DNA bases 8-hydroxy-2'-deoxyguanosine (8-OHdG), a potential marker involved in the initiation of carcinogenesis, were measured by high-performance liquid chromatography, whereas tissue trace element status and expression of metallothionein (MT), a Cu-Zn metalloprotein associated with neoplastic cell growth and subsequent development of premalignant phenotype of the cell, were studied by energy-dispersive X-ray fluorescence spectrometry and enzyme-coupled immunohistochemistry, respectively. There was a significant and steady elevation of modified bases (8-OHdG) along with substantial increase in MT immunoexpression and disturbance in trace element homeostasis following DEN exposure. Supplementation of vanadium at a dose of 0.5 ppm for four consecutive weeks strictly abated the formation of 8-OHdG (P < 0.0001; 81.28%) in preneoplastic rat liver. In a long-term DEN plus PB regimen, vanadium was able to limit in situ MT expression with a concomitant decrease in MT immunoreactivity (P < 0.05). Furthermore, vanadium treatment throughout the study restored hepatic levels of essential trace elements and decreased nodular incidence (58.34%) and nodule multiplicity (P < 0.001; 66.89%) in rats treated with DEN plus PB. Taken together, the study provides evidence in support of the chemopreventive potential of vanadium in limiting neoplastic transformation during the preneoplastic stages of hepatocarcinogenesis in rats.

Vanadium inhibits the development of 2-acetylaminofluorene-induced premalignant phenotype in a two-stage chemical rat hepatocarcinogenesis model

In recent years, research on the biological influence of micronutrients in cancer has grown enormously. Among these, vanadium, a dietary micronutrient present in mammalian tissues has received considerable attention as a limiting agent. In the present study, attempts have been made to investigate the in vivo antitumour potentials of this micronutrient at the 0.5 ppm dosage in drinking water in a defined model of a two-stage experimental rat hepatocarcinogenesis. The chemopreventive effect of vanadium was assessed by studying certain biomarkers, such as development of gamma-glutamyltranspeptidase (GGT)-positive foci, levels of some essential trace elements, in situ expression of proliferating cell nuclear antigen (PCNA) and chromosomal aberrations. Hepatocarcinogenesis was induced in male Sprague-Dawley rats by chronic feeding of 2-acetylaminofluorene (0.05% in basal diet) on and from week 4. Vanadium administration throughout the experiment reduced the relative liver weight, nodular incidence (66.70%), total number and multiplicity (79.93%) and restored hepatic levels of selenium (Se) and iron (Fe) (P < 0.001) when compared to the carcinogen control. Moreover, long-term vanadium treatment significantly abated the expressions of GGT (P < 0.001) and PCNA with concomitant reduction in PCNA immunolabeling index (P < 0.001; 36.62%). Finally, the anticlastogenic potential of vanadium was reflected through its ability to inhibit early chromosomal aberrations (P < 0.001; 45.17%) in 2-AAF-challenged rat hepatocytes. Our results suggest that supplementary vanadium at a dose of 0.5 ppm, when administered continuously throughout the study, than administered either in the initiation or promotion phase alone, is very much effective in suppressing neoplastic transformation in vivo. We conclude the significant role of vanadium in limiting cell proliferation and chromosomal aberrations during the preneoplastic stages of hepatocarcinogenesis in rats.

Vanadium induces apoptosis and modulates the expressions of metallothionein, Ki-67 nuclear antigen, and p53 during 2-acetylaminofluorene-induced rat liver preneoplasia

Our previous studies have shown that vanadium, a dietary micronutrient, has an inhibitory effect against experimentally induced rat hepatocarcinogenesis. In this study, we evaluated the role of vanadium on some potential protein expression markers of carcinogenesis, such as metallothionein (MT), an intracellular metal-binding protein linked with cell proliferation and apoptosis, Ki-67 nuclear antigen, and p53 tumor suppressor during 2-acetylaminofluorene (2-AAF)-induced (0.05% in basal diet) rat liver preneoplasia. In a short-term regimen, supplementation of vanadium at a dose of 0.5 ppm effectively suppressed the formation of DNA 'comets' (29.55%; P < 0.02), thereby indicating its nongenotoxicity at this particular dose. Vanadium administration throughout the study reduced relative liver weight (RLW), nodular incidence (57.15%), total number, and multiplicity (48.45%) with restoration of hepatic zinc (Zn), magnesium (Mg), selenium (Se), copper (Cu), iron (Fe), and calcium (Ca) contents when compared to the carcinogen control. Moreover, treatment with vanadium significantly abated the expressions of MT and Ki-67, studied at four sequential time points. An increased immunopositivity of p53 protein (1.03 +/- 0.23%; P < 0.02) was found in vanadium-treated rat liver with an elevated apoptotic-labeling index (AI; P < 0.001) as documented by TUNEL assay. Furthermore, a positive correlation between MT expression and Ki-67 labeling along with a strong negative correlation between MT immunoreactivity and AI (r = -0.9000, P = 0.0004 at week 24) at various time intervals suggest that, vanadium-mediated suppression of MT and Ki-67 expressions may be associated with induction of apoptosis. The results thus provide evidence for the first time in support of the potential role of vanadium on induction of p53 and apoptosis with concurrent suppression of MT and Ki-67 in order to have an understanding, in part, of the chemopreventive mechanism of this trace element in limiting neoplastic transformation in a defined model of experimental rat hepatocarcinogenesis.

Enzymatic detection of precursor cell populations of preneoplastic foci positive for gamma-glutamyltranspeptidase in rat liver

An improved staining method for gamma-glutamyltranspeptidase (GGT) was developed using Vibratome-prepared microslices. Microscopic precursor cell populations of preneoplastic foci positive for the marker enzyme were detectable sequentially in rat liver by tracing back from 5 to 1 week after carcinogen injection in a hepatocarcinogenesis model. Mirror-image comparisons of serial sections stained for GGT activity and immunocytochemically stained for GST-P (glutathione S-transferase P-form) revealed that GGT expression was confined within GST-P(+) cell populations (GST-P(+) minifoci), which are induced in the periportal area (zone 1) of the liver. GGT expression level differed from one minifocus to another, and the larger the GST-P(+) focus, the stronger was the GGT expression in it, indicating that GST-P(+)/GGT(-) phenotypes are convertible into proliferating GST-P(+)/GGT(+) ones. Our results suggest that there are at least 2 closely related precursors, GST-P(+)/GGT(-) and GST-P(+)/GGT(+) phenotypes, of preneoplastic foci in rat chemical hepatocarcinogenesis.

Inhibitory effect of celery seeds extract on chemically induced hepatocarcinogenesis: modulation of cell proliferation, metabolism and altered hepatic foci development

The chemopreventive activity of methanolic extract of Apium graveolens seeds (celery seeds) has been investigated against Solt Farber protocol of hepatocarcinogenesis, oxidative stress and induction of positive foci of gamma-GT in the liver of Wistar rats. The prophylactic treatment of celery seeds extract protected dose dependently against diethylnitrosoamine (DEN)+2-acetylaminofluorine (AAF)+partial hepatectomy (PH) induced hepatocarcinogenesis and other related events such as induction of gamma-GT positive foci (P<0.001). 2-AAF administration in diet with PH in rats resulted in increased hepatic ornithine decarboxylase (ODC) activity and a consequent increase in the rate of DNA synthesis when compared to saline treated control group while pretreatment of rats with celery seeds extract resulted in inhibition of aforementioned parameters dose dependently. The augmentation of quinone reductase (QR), glutathione-S-transferase (GST) and serum gamma-glutamyl transpeptidase (GGT) activities; and depletion of the tissue GSH content after 2-AAF (i.p. injection) for five consecutive days was prevented with the administration of celery seed extract. On the basis of the above results it can be said that A. graveolens is a potent plant against experimentally induced hepatocarcinogenesis in Wistar rats.

Epidemiology and natural history of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a major contributor to cancer incidence and mortality. There is a wide variation, however, in the global distribution of HCC. Eighty percent of the burden is borne by countries in Asia and sub-Saharan Africa. In most high-risk countries, principal risk factors include infection with hepatitis B virus and dietary exposure to aflatoxin B(1). In contrast, hepatitis C virus and alcohol consumption are more important risk factors in low-risk countries. In recent years, the incidence of HCC has decreased in some high-risk countries and increased in some low-risk countries. Reasons for both trends are not completely understood, but are likely related to public health efforts in Asia and the increase in hepatitis C virus infection in low-risk countries. Vaccination programs against hepatitis B virus will likely decrease the HCC rate even further in decades to come.

Proliferative activity in postmenopausal endometrium: the lurking potential for giving rise to an endometrial adenocarcinoma

AIMS

To investigate proliferation in disease free postmenopausal endometrium and that harbouring endometrial adenocarcinoma-is there a dynamic, yet lurking, potential for atrophic endometrium to give rise to endometrial adenocarcinoma?

MATERIAL/METHODS

The study comprised 84 disease free endometria from asymptomatic postmenopausal women who had undergone hysterectomy for prolapse, and 50 endometrioid cell type endometrial adenocarcinomas with adjacent uninvolved postmenopausal endometrium. The non-neoplastic tissues were separated histologically into active, inactive, and mixed forms, although only the first two categories were studied immunohistochemically for oestrogen and progesterone receptors (ERs, PRs), epidermal growth factor receptor (EGFR), Ki-67, and angiogenic activity.

RESULTS

All postmenopausal endometria were atrophic, but only 42 were inactive; of the remaining samples, 22 were weakly proliferative and 20 were mixed active and inactive. In contrast, the non-neoplastic component of 43 of the 50 endometrial adenocarcinomas examined was of the active form; four specimens were of the pure and 39 of the mixed form. Interestingly, high ER and PR expression was seen in active and inactive endometria, but only the former were EGFR positive and had high proliferative (Ki-67) and angiogenic activity. A similar trend was also shown by the non-neoplastic atrophic endometrium adjacent to endometrial adenocarcinoma.

CONCLUSIONS

At least half of the disease free postmenopausal atrophic endometria show a weak proliferative pattern, either diffuse or focal, probably as a response to continuous low level oestrogenic stimulation. These tissues have a latent, although very small, carcinogenic potential, as demonstrated by the immunohistochemical profile and their frequent association with adjacent endometrial adenocarcinoma.

Genetic and cellular mechanisms in chromium and nickel carcinogenesis considering epidemiologic findings

Genetic and environmental interactions determine cancer risks but some cancer incidence is primarily a result of inherited genetic deficits alone. Most cancers have an occupational, viral, nutritional, behavioral or iatrogenic etiology. Cancer can sometimes be controlled through broad public health interventions including industrial hygiene and engineering controls. Chromium and nickel are two human carcinogens associated with industrial exposures where public health measures apparently work. Carcinogenic mechanisms of these metals are examined by electron-spin-resonance-spectroscopy and somatic-mutation-and-recombination in Drosophila melanogaster in this report. Both metals primarily affect initiation processes in cancer development suggesting important theoretical approaches to prevention and followup.

GSTP1 CpG island hypermethylation as a molecular biomarker for prostate cancer

Somatic hypermethylation of CpG island sequences at GSTP1, the gene encoding the pi-class glutathione S-transferase, appears to be characteristic of human prostatic carcinogenesis. To consider the potential utility of this epigenetic alteration as a biomarker for prostate cancer, we present here a comprehensive review of the literature describing somatic GSTP1 changes in DNA from prostate cells and tissues. GSTP1 CpG island hypermethylation has been detected in prostate cancer DNA using a variety of assay techniques, including (i) Southern blot analysis (SB), after treatment with (5-m)C-sensitive restriction endonucleases, (ii) the polymerase chain reaction, following treatment with (5-m)C-sensitive restriction endonucleases (RE-PCR), (iii) bisulfite genomic sequencing (BGS), and (iv) bisulfite modification followed by the polymerase chain reaction, using primers selective for target sequences containing (5-m)C (MSP). In the majority of the case series so far reported, GSTP1 CpG island hypermethylation was present in DNA from at least 90% of prostate cancer cases. When analyses have been carefully conducted, GSTP1 CpG island hypermethylation has not been found in DNA from normal prostate tissues, or from benign prostatic hyperplasia (BPH) tissues, though GSTP1 CpG island hypermethylation changes have been detected in DNA from candidate prostate cancer precursor lesions proliferative inflammatory atrophy (PIA) and prostatic intraepithelial neoplasia (PIN). Using PCR methods, GSTP1 CpG island hypermethylation has also been detected in urine, ejaculate, and plasma from men with prostate cancer. GSTP1 CpG island hypermethylation, a somatic epigenetic alteration, appears poised to serve as a molecular biomarker useful for prostate cancer screening, detection, and diagnosis.

Vanadium suppresses sister-chromatid exchange and DNA-protein crosslink formation and restores antioxidant status and hepatocellular architecture during 2-acetylaminofluorene-induced experimental rat hepatocarcinogenesis

Vanadium is an important regulator of cellular growth, differentiation, and cell death, and thus has received increasing attention to be an effective cancer chemopreventive agent. In the present study, attempts have been made to investigate the in vivo antineoplastic effect of this micronutrient at the 0.5 ppm dosage in drinking water, by monitoring hepatic nodulogenesis and hepatocellular phenotype followed by antioxidant status and atomic absorption spectrometric estimation of some essential biometals during the multistage of carcinogenesis induced by 2-acetylaminofluorene (2-AAF; 0.05% in basal diet). Finally, sister-chromatid exchange (SCE) and DNA-protein crosslink (DPC) formation, as potential biomarkers were estimated to find out the suppressive effect of vanadium at the molecular level. The results showed that vanadium administration throughout the experiment reduced the relative liver weight, nodular incidence (48.40%), total number, and multiplicity (63.91%), and altered the size of visible persistent nodules (PNs) with concurrent restoration of hepatic glutathione (P < 0.01), glutathione-S-transferase (P < 0.001) and manganese-dependent superoxide dismutase (P < 0.001) activities as well as, hepatic zinc and copper contents (P < 0.001) when compared to the carcinogen control. Moreover, vanadium treatment significantly reduced SCE frequency (50.24%) and DPC coefficient (P < 0.001; 21.30%). Our results, thus, strongly suggest that supplementary vanadium at a dose of 0.5 ppm, when administered continuously throughout the study, than administered either in the initiation or promotion phase alone, is very much effective in suppressing neoplastic transformation during 2-AAF-induced in vivo rat hepatocarcinogenesis.

The role of hepatocytes and oval cells in liver regeneration and repopulation

The liver has the unique capacity to regulate its growth and mass. In rodents and humans, it grows rapidly after resection of more than 50% of its mass. This growth process, as well as that following acute chemical injury is known as liver regeneration, although growth takes place by compensatory hyperplasia rather than true regeneration. In addition to hepatocytes and non-parenchymal cells, the liver contains intra-hepatic "stem" cells which can generate a transit compartment of precursors named oval cells. Liver regeneration after partial hepatectomy does not involve intra or extra-hepatic (hemopoietic) stem cells but depends on the proliferation of hepatocytes. Transplantation and repopulation experiments have demonstrated that hepatocytes, which are highly differentiated and long-lived cells, have a remarkable capacity for multiple rounds of replication. In this article, we review some aspects of the regulation of hepatocyte proliferation as well as the interrelationships between hepatocytes and oval cells in different liver growth processes. We conclude that in the liver, normally quiescent differentiated cells replicate rapidly after tissue resection, while intra-hepatic precursor cells (oval cells) proliferate and generate lineage only in situations in which hepatocyte proliferation is blocked or delayed. Although bone marrow stem cells can generate oval cells and hepatocytes, transdifferentiation is very rare and inefficient.

K vitamins, PTP antagonism, and cell growth arrest

The main function of K vitamins is to act as co-factors for gamma-glutamyl carboxylase. However, they have also recently been shown to inhibit cell growth. We have chemically synthesized a series of K vitamin analogs with various side chains at the 2 or 3 position of the core naphthoquinone structure. The analogs with short thio-ethanol side chains are found to be more potent growth inhibitors in vitro of various tumor cell lines. Cpd 5 or [2-(2-mercaptoethanol)-3-methyl-1,4-naphthoquinone] is one of the most potent. The anti-proliferation activity of these compounds is antagonized by exogenous thiols but not by non-thiol antioxidants. This suggests that the growth inhibition is mediated by sulfhydryl arylation of cellular glutathione and cysteine-containing proteins and not by oxidative stress. The protein tyrosine phosphatases (PTP) are an important group of proteins that contain cysteine at their catalytic site. PTPs regulate mitogenic signal transduction and cell cycle progression. PTP inhibition by Cpd 5 results in prolonged tyrosine phosphorylation and activation of several kinases and transcription factors including EGFR, ERK1/2, and Elk1. Cpd 5 could activate ERK1/2 either by signaling from an activated EGFR, which is upstream in the signaling cascade, or by direct inhibition of ERK1/2 phosphatase(s). Prolonged ERK1/2 phosphorylation strongly correlates with Cpd 5-mediated growth inhibition. Cpd 5 can also bind to and inhibit the Cdc25 family of dual specific phosphatases. As a result, several Cdc25 substrates (Cdk1, Cdk2, Cdk4) involved in cell cycle progression are tyrosine phosphorylated and thereby inhibited by its action. Cpd 5 could also inhibit both normal liver regeneration and hepatoma growth in vivo. DNA synthesis during rat liver regeneration following partial hepatectomy, transplantable rat hepatoma cell growth, and glutathione-S-transferase-pi expressing hepatocytes after administration of the chemical carcinogen diethylnitrosamine, are all inhibited by Cpd 5 administration. The growth inhibitory effect during liver regeneration and transplantable tumor growth is also correlated with ERK1/2 phosphorylation induced by Cpd 5. Thus, Cpd 5-mediated inhibition of PTPs, such as Cdc25 leads to cell growth arrest due to altered activity of key cellular kinases involved in signal transduction and cell cycle progression. This prototype K vitamin analog represents a novel class of growth inhibitor based upon its action as a selective PTP antagonist. It is clearly associated with prolonged ERK1/2 phosphorylation, which is in contrast with the transient ERK1/2 phosphorylation induced by growth stimulatory mitogens.

Expression of the lung resistance-related protein in human and rat hepatocarcinogenesis

Lung resistance-related protein (LRP) plays an important role in chemoresistance of tumor cells probably by altering nuclear-cytoplasmic transport processes. We analyzed the association between LRP expression and hepatocarcinogenesis in humans and rats by RT-PCR, immunoblotting, and immunohistochemistry. LRP was found in hepatocytes and bile epithelia of normal human and rat liver showing distinct interindividual variations. In human tissues, the LRP expression levels of dysplastic liver nodules, hepatocellular adenomas, and carcinomas were highly variable, including decreased but also distinctly increased staining intensities. Mean expression levels, however, were comparable to the surrounding tissue. Considerable levels of LRP mRNA and protein were also found in human hepatoma cell lines. To study LRP expression from the beginning of hepatocarcinogenesis onward, rats were subjected to a tumor initiation/promotion protocol leading to preneoplastic hepatocytes present as single cells or multicellular clones, followed by adenoma and carcinoma. All of the (pre)neoplastic rat liver lesions expressed, comparable to the surrounding tissue, considerable amounts of LRP. We conclude that LRP might be one mechanism involved in the intrinsically high but variable chemoresistance of normal and (pre)neoplastic hepatocytes.

Effects of the porphyrinogenic compounds hexachlorobenzene and 3,5-diethoxycarbonyl-1,4-dihydrocollidine on polyamine metabolism

The naturally occurring polyamines--putrescine, spermidine and spermine--are organic cations present in all living cells and essential for cell growth and differentiation. The aim of the present study was to extend the investigations on the effects of porphyrinogenic compounds on polyamine metabolism. This was achieved by studying putrescine, spermidine and spermine levels in a model of acute porphyria, i.e. 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC)-induced porphyria, and in a model of non-acute porphyria, i.e. hexachlorobenzene (HCB)-induced porphyria. HCB administration to female Wistar rats for 7, 14, 21, 28 and 56 days did not alter polyamine levels in liver, even though rats presented clear signs of HCB-induced porphyria. In contrast to HCB, DDC treatment resulted in a remarkable increase in putrescine levels in the liver of female and male Sprague-Dawley rats. This increase was due, at least in part, to ornithine decarboxylase (ODC) activation. DDC induction of putrescine levels did not show organ specificity, since it could also be seen in adrenal gland. Interestingly, the deregulation of polyamine biosynthesis occurred concomitantly with the deregulation of the heme biosynthetic pathway. In addition to porphyria, it is known that DDC intoxication affects several proteins of the hepatocyte cytoskeleton. It is suggested that DDC-induced increase in ODC activity and putrescine levels may be an early event contributing to alter the cytoskeleton.