Alternative methods of selecting rat hepatocellular nodules resistant to 2-acetylaminofluorene

Iron-saturated bovine lactoferrin: a promising chemopreventive agent for hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a tumor with minimal chance of cure due to underlying liver diseases, late diagnosis, and inefficient treatments. Thus, HCC treatment warrants the development of additional strategies. Lactoferrin (Lf) is a mammalian multifunctional iron-binding glycoprotein of the innate immune response and can be found as either a native low iron form (native-Lf) or a high iron form (holo-Lf). Bovine Lf (bLf), which shares many functions with human Lf (hLf), is safe for humans and has several anticancer activities, including chemotherapy boost in cancer. We found endogenous hLf is downregulated in HCC tumors compared with normal liver, and decreased hLf levels in HCC tumors are associated with shorter survival of HCC patients. However, the chemoprotective effect of 100% iron saturated holo-bLf on experimental hepatocarcinogenesis has not yet been determined. We aimed to evaluate the chemopreventive effects of holo-bLf in different HCC models. Remarkably, a single dose (200 mg kg-1) of holo-bLf was effective in preventing early carcinogenic events in a diethylnitrosamine induced HCC in vivo model, such as necrosis, ROS production, and the surge of facultative liver stem cells, and eventually, holo-bLf reduced the number of preneoplastic lesions. For an established HCC model, holo-bLf treatment significantly reduced HepG2 tumor burden in xenotransplanted mice. Finally, holo-bLf in combination with sorafenib, the advanced HCC first-line treatment, synergistically decreased HepG2 viability by arresting cells in the G0/G1 phase of the cell cycle. Our findings provide the first evidence suggesting that holo-bLf has the potential to prevent HCC or to be used in combination with treatments for established HCC.

Hepatoprotective Effect Assessment of C-Phycocyanin on Hepatocellular Carcinoma Rat Model by Using Photoacoustic Spectroscopy

Hepatocellular carcinoma (HCC) is the most common primary neoplasia of the liver with elevated mortality. Experimental treatment with antioxidants has a beneficial effect on the experimental models of HCC. Arthrospira maxima (spirulina) and its phycocyanin have antitumoral action on different tumoral cells. However, it is unknown whether phycocyanin is the responsible molecule for the antitumoral effect on HCC. Photoacoustic spectroscopy (PAS) stands out among other spectroscopy techniques for its versatility of samples analyzed. This technique makes it possible to obtain the optical absorption spectrum of solid or liquid, dark or transparent samples. Previous studies report that assessing liver damage in rats produced by the modified resistant hepatocyte model (MRHM) is possible by analyzing their blood optical absorption spectrum. This study aimed to investigate, by PAS, the effect of phycocyanin obtained from spirulina on hepatic dysfunction. The optical absorption spectra analysis of the rat blood indicates the damage level induced by the MRHM group, being in concordance with the carried out biological conventional studies results, indicating an increase in the activity of hepatic enzymes, oxidative stress, Bax/Bcl2 ratio, cdk2, and AKT2 expression results, with a reduction in p53 expression. Also, PAS results suggest that phycocyanin decreases induced damage, due to the prevention of the Bax, AKT2, and p53 altered expression and the tumor progression in a HCC rat model.

Past, present, and future of chemically induced hepatocarcinogenesis rodent models: Perspectives concerning classic and new cancer hallmarks

Hepatocellular carcinoma (HCC), the main primary liver cancer, accounts for 5 % of all incident cases and 8.4 % of all cancer-related deaths worldwide. HCC displays a spectrum of environmental risk factors (viral chronic infections, aflatoxin exposure, alcoholic- and nonalcoholic fatty liver diseases) that result in molecular complexity and heterogeneity, contributing to a rising epidemiological burden, poor prognosis, and non-satisfactory treatment options. The emergence of HCC (i.e., hepatocarcinogenesis) is a multistep and complex process that addresses many (epi)genetic alterations and phenotypic traits, the so-called cancer hallmarks. "Polymorphic microbiomes", "epigenetic reprogramming", "senescent cells" and "unlocking phenotypic plasticity" are trending hallmarks/enabling features in cancer biology. As the main molecular drivers of HCC are still undruggable, chemically induced in vivo models of hepatocarcinogenesis are useful tools in preclinical research. Thus, this narrative review aimed at recapitulating the basic features of chemically induced rodent models of hepatocarcinogenesis, eliciting their permanent translational value regarding the "classic" and the "new" cancer hallmarks/enabling features. We gathered state-of-art preclinical evidence on non-cirrhotic, inflammation-, alcoholic liver disease- and nonalcoholic fatty liver-associated HCC models, demonstrating that these bioassays indeed express the recently added hallmarks, as well as reflect the interplay between classical and new cancer traits. Our review demonstrated that these protocols remain valuable for translational preclinical application, as they recapitulate trending features of cancer science. Further "omics-based" approaches are warranted while multimodel investigations are encouraged in order to avoid "model-biased" responses.

In Vivo and In Vitro Models of Hepatocellular Carcinoma: Current Strategies for Translational Modeling

Hepatocellular carcinoma (HCC) is the sixth most common cancer worldwide and the third leading cause of cancer-related death globally. HCC is a complex multistep disease and usually emerges in the setting of chronic liver diseases. The molecular pathogenesis of HCC varies according to the etiology, mainly caused by chronic hepatitis B and C virus infections, chronic alcohol consumption, aflatoxin-contaminated food, and non-alcoholic fatty liver disease associated with metabolic syndrome or diabetes mellitus. The establishment of HCC models has become essential for both basic and translational research to improve our understanding of the pathophysiology and unravel new molecular drivers of this disease. The ideal model should recapitulate key events observed during hepatocarcinogenesis and HCC progression in view of establishing effective diagnostic and therapeutic strategies to be translated into clinical practice. Despite considerable efforts currently devoted to liver cancer research, only a few anti-HCC drugs are available, and patient prognosis and survival are still poor. The present paper provides a state-of-the-art overview of in vivo and in vitro models used for translational modeling of HCC with a specific focus on their key molecular hallmarks.

Butyrate-containing structured lipids act on HDAC4, HDAC6, DNA damage and telomerase activity during promotion of experimental hepatocarcinogenesis

Hepatocellular carcinoma (HCC) presents with a high treatment resistance and poor prognosis. Early diagnosis and preventive approaches such as chemoprevention are essential for the HCC control. Therefore, we evaluated the chemopreventive effects of butyrate-containing structured lipids (STLs) administered during the promotion stage of hepatocarcinogenesis in rats submitted to the 'resistant hepatocyte' (RH) model. Administration of butyrate-containing STLs inhibited the incidence and mean number of visible hepatic nodules per rat and reduced the number and area of glutathione S-transferase placental form-positive (GST-P+) preneoplastic focal lesions in the livers. This was accompanied by the induction of apoptosis and an increased level of hepatic butyric acid. Treatment with butyrate-containing STLs resulted in increased histone H3 lysine 9 (H3K9) acetylation, reduction of total histone deacetylase (HDAC) activity, and lower levels of HDAC4 and HDAC6 proteins. The chemopreventive effect of butyrate-containing STLs was also associated with the increased nuclear compartmentalization of p53 protein and reduced expression of the Bcl-2 protein. In addition, rats treated with butyrate-containing STLs showed decreased DNA damage and telomerase activity in the livers. These results demonstrate that the suppressive activity of butyrate-containing STLs is associated with inhibition of elevated during hepatocarcinogenesis chromatin-modifying proteins HDAC4 and HDAC6, subcellular redistribution of the p53 protein, and decreased DNA damage and telomerase activity.

Butyrate-containing structured lipids inhibit RAC1 and epithelial-to-mesenchymal transition markers: a chemopreventive mechanism against hepatocarcinogenesis

Hepatocellular carcinoma (HCC) is one of the most aggressive human cancers. The rising incidence of HCC worldwide and its resistance to pharmacotherapy indicate that the prevention of HCC development may be the most impactful strategy to improve HCC-related morbidity and mortality. Among the broad range of chemopreventive agents, the use of dietary and nutritional agents is an attractive and promising approach; however, a better understanding of the mechanisms of their potential cancer suppressive action is needed to justify their use. In the present study, we investigated the underlying molecular pathways associated with the previously observed suppressive effect of butyrate-containing structured lipids (STLs) against liver carcinogenesis using a rat "resistant hepatocyte" model of hepatocarcinogenesis that resembles the development of HCC in humans. Using whole transcriptome analysis, we demonstrate that the HCC suppressive effect of butyrate-containing STLs is associated with the inhibition of the cell migration, cytoskeleton organization, and epithelial-to-mesenchymal transition (EMT), mediated by the reduced levels of RACGAP1 and RAC1 proteins. Mechanistically, the inhibition of the Racgap1 and Rac1 oncogenes is associated with cytosine DNA and histone H3K27 promoter methylation. Inhibition of the RACGAP1/RAC1 oncogenic signaling pathways and EMT may be a valuable approach for liver cancer prevention.

Aging promotes neoplastic disease through effects on the tissue microenvironment

A better understanding of the complex relationship between aging and cancer will provide important tools for the prevention and treatment of neoplasia. In these studies, the hypothesis was tested that aging may fuel carcinogenesis via alterations imposed in the tissue microenvironment. Preneoplastic hepatocytes isolated from liver nodules were orthotopically injected into either young or old syngeneic rats and their fate was followed over time using the dipeptidyl-peptidase type IV (DPPIV) system to track donor-derived-cells. At 3 months post-Tx, the mean size of donor-derived clusters was 11±3 cells in young vs. 42±8 in old recipients. At 8 months post-Tx, no visible lesion were detected in any of 21 young recipients, while 17/18 animals transplanted at old age displayed hepatic nodules, including 7 large tumors. All tumors expressed the DPPIV marker enzyme, indicating that they originated from transplanted cells. Expression of senescence-associated β-galactosidase was common in liver of 18-month old animals, while it was a rare finding in young controls. Finally, both mRNA and IL6 protein were found to be increased in the liver of aged rats compared to young controls. These results are interpreted to indicate that the microenvironment of the aged liver promotes the growth of pre-neoplastic hepatocytes.

Gene silencing of Nox4 by CpG island methylation during hepatocarcinogenesis in rats

The association between the downregulation of genes and DNA methylation in their CpG islands has been extensively studied as a mechanism that favors carcinogenesis. The objective of this study was to analyze the methylation of a set of genes selected based on their microarray expression profiles during the process of hepatocarcinogenesis. Rats were euthanized at: 24 h, 7, 11, 16 and 30 days and 5, 9, 12 and 18 months post-treatment. We evaluated the methylation status in the CpG islands of four deregulated genes (Casp3, Cldn1, Pex11a and Nox4) using methylation-sensitive high-resolution melting technology for the samples obtained from different stages of hepatocarcinogenesis. We did not observe methylation in Casp3, Cldn1 or Pex11a. However, Nox4 exhibited altered methylation patterns, reaching a maximum of 10%, even during the early stages of hepatocarcinogenesis. We observed downregulation of mRNA and protein of Nox4 (97.5% and 40%, respectively) after the first carcinogenic stimulus relative to the untreated samples. Our results suggest that Nox4 downregulation is associated with DNA methylation of the CpG island in its promoter. We propose that methylation is a mechanism that can silence the expression of Nox4, which could contribute to the acquisition of neoplastic characteristics during hepatocarcinogenesis in rats.

Summary: Many genes downregulated by DNA methylation are tumor suppressor genes. In the present study, DNA methylation of Nox4 is observed, with implications for Nox4 as a potential therapeutic target for liver or other cancers.

Suppressing activity of tributyrin on hepatocarcinogenesis is associated with inhibiting the p53-CRM1 interaction and changing the cellular compartmentalization of p53 protein

Hepatocellular carcinoma (HCC), an aggressive and the fastest growing life-threatening cancer worldwide, is often diagnosed at intermediate or advanced stages of the disease, which substantially limits therapeutic approaches for its successful treatment. This indicates that the prevention of hepatocarcinogenesis is probably the most promising approach to reduce both the HCC incidence and cancer-related mortality. In previous studies, we demonstrated a potent chemopreventive effect of tributyrin, a butyric acid prodrug, on experimental hepatocarcinogenesis. The cancer-inhibitory effect of tributyrin was linked to the suppression of sustained cell proliferation and induction of apoptotic cell death driven by an activation of the p53 apoptotic signaling pathway. The goal of the present study was to investigate the underlying molecular mechanisms linked to tributyrin-mediated p53 activation. Using in vivo and in vitro models of liver cancer, we demonstrate that an increase in the level of p53 protein in nuclei, a decrease in the level of cytoplasmic p53, and, consequently, an increase in the ratio of nuclear/cytoplasmic p53 in rat preneoplastic livers and in rat and human HCC cell lines caused by tributyrin or sodium butyrate treatments was associated with a marked increase in the level of nuclear chromosome region maintenance 1 (CRM1) protein. Mechanistically, the increase in the level of nuclear p53 protein was associated with a substantially reduced binding interaction between CRM1 and p53. The results demonstrate that the cancer-inhibitory activity of sodium butyrate and its derivatives on liver carcinogenesis may be attributed to retention of p53 and CRM1 proteins in the nucleus, an event that may trigger activation of p53-mediated apoptotic cell death in neoplastic cells.

The chemopreventive activity of butyrate-containing structured lipids in experimental rat hepatocarcinogenesis

SCOPE

Emerging evidence indicates that the use of bioactive food components is a promising strategy to prevent the development of liver cancer. The goal of this study was to examine the chemopreventive effect of butyrate-containing structured lipids (STLs) produced by an enzymatic interesterification of tributyrin and flaxseed oil on rat hepatocarcinogenesis.

METHODS AND RESULTS

Male Wistar rats were subjected to a classic "resistant hepatocyte" model of liver carcinogenesis and treated with STLs, tributyrin or flaxseed oil during the initial phases of hepatocarcinogenesis. Treatment with STLs and tributyrin strongly inhibited the development of preneoplastic liver lesions. The chemopreventive activity of tributyrin was associated with the induction of apoptosis and reduction of the expression of major activated hepatocarcinogenesis-related oncogenes. Treatment with STLs caused substantially greater inhibitory effects than tributyrin on oncogene expression.

CONCLUSION

These results demonstrate that the tumor-suppressing activity of butyrate-containing STLs is associated with its ability to prevent and inhibit activation of major hepatocarcinogenesis-related oncogenes. Enrichment of histone H3K9me3 and H3K27me3 at the promoter of Myc and Ccnd1 genes may be related to the inhibitory effect on oncogene expression in the livers of STL-treated rats.

Induction of an altered lipid phenotype by two cancer promoting treatments in rat liver

Changes in lipid metabolism have been associated with tumor promotion in rat liver. Similarities and differences of lipid parameters were investigated using the mycotoxin fumonisin B1 (FB1) and the 2-acetylaminofluorene/partial hepatectomy (AAF/PH) treatments as cancer promoters in rat liver. A typical lipid phenotype was observed, including increased membranal phosphatidylethanolamine (PE) and cholesterol content, increased levels of C16:0 and monounsaturated fatty acids in PE and phosphatidylcholine (PC), as well as a decrease in C18:0 and long-chained polyunsaturated fatty acids in the PC fraction. The observed lipid changes, which likely resulted in changes in membrane structure and fluidity, may represent a growth stimulus exerted by the cancer promoters that could provide initiated cells with a selective growth advantage. This study provided insight into complex lipid profiles induced by two different cancer promoting treatments and their potential role in the development of hepatocyte nodules, which can be used to identify targets for the development of chemopreventive strategies against cancer promotion in the liver.

Transcriptomic responses provide a new mechanistic basis for the chemopreventive effects of folic acid and tributyrin in rat liver carcinogenesis

The steady increase in the incidence and mortality of hepatocellular carcinoma (HCC) signifies a crucial need to understand better its pathogenesis to improve clinical management and prevention of the disease. The aim of this study was to investigate molecular mechanisms for the chemopreventive effects of folic acid and tributyrin alone or in combination on rat hepatocarcinogenesis. Male Wistar rats were subjected to a classic "resistant hepatocyte" model of liver carcinogenesis and treated with folic acid and tributyrin alone or in combination for 5 weeks during promotion stage. Treatment with folic acid and tributyrin alone or in combination strongly inhibited the development of glutathione-S-transferase placental form (GSTP)-positive foci. Microarray analysis showed significant changes in gene expression. A total of 498, 655 and 940 of differentially expressed genes, involved in cell cycle, p53-signaling, angiogenesis and Wnt pathways, was identified in the livers of rats treated with folic acid, tributyrin or folic acid and tributyrin. A detailed analysis of these differentially expressed genes revealed that treatments inhibited angiogenesis in the preneoplastic livers. This was evidenced by the fact that 30 out of 77 differentially expressed genes common to all three treatments are involved in the regulation of the angiogenesis pathway. The inhibition of angiogenesis was confirmed by reduced levels of CD34 protein. In conclusion, the tumor-suppressing activity of folic acid and tributyrin is associated with inhibition of angiogenesis at early stages of rat liver carcinogenesis. Importantly, the combination of folic acid and tributyrin has stronger chemopreventive effect than each of the compounds alone.

β-ionone inhibits persistent preneoplastic lesions during the early promotion phase of rat hepatocarcinogenesis: TGF-α, NF-κB, and p53 as cellular targets

Dietary isoprenic derivatives such as β-ionone (βI) are a promising class of chemopreventive agents. In this study, cellular aspects of βI protective activities during early hepatocarcinogenesis were evaluated. Male Wistar rats were submitted to "resistant hepatocyte" model and then received daily 16 mg/100 g body weight (b.w.) of βI (βI group) or only 0.25 mL/100 g b.w. of corn oil (vehicle, control group [CO]) during 4 wk, specifically during early promotion phase. Compared to controls, βI inhibited (P < 0.05) the development of persistent preneoplastic lesions (pPNL), considered to be potential hepatocellular carcinoma (HCC) progression sites, and increased remodeling PNL (rPNL) (P < 0.05) that tend to regress to a normal phenotype. Increased βI hepatic levels (P < 0.05), in the βI group, were associated with its chemopreventive actions. Compared to control rats, βI reduced the frequency of both pPNL and rPNL positive for tumor growth factor (TGF)-α (P < 0.05), reduced the frequency of pPNL stained for p65 (nuclear factor-kappaB; NF-κB) (P < 0.05), and reduced the frequency of pPNL positive for cytoplasmic p53 (P < 0.05). Our data demonstrated that βI targets TGF-α, NF-κB, and p53 in initial phases of hepatocarcinogenesis and specifically inhibits PNL with increased probability to progress to HCC. This isoprenoid may represent a chemopreventive agent of choice for HCC control.

The effect of caffeic acid phenethyl ester analogues in a modified resistant hepatocyte model

We present a study of the chemoprotective effects of two caffeic acid phenethyl ester (CAPE)-related structures: LQM717 and LQM706. The modified resistant hepatocyte model in rats was used to study the chemoprevention of these CAPE analogues, which are inexpensive and easily obtained. In the liver cancer model used, we detected extensive necrosis and lipid peroxidation after 24 h, many altered hepatic foci, putatively preneoplastic lesions with γ-glutamyl transpeptidase staining after 30 days, and liver tumors at 12 months. We tested the effect of the CAPE analogues on necrosis, lipid peroxidation, proliferation, p65 activation, altered hepatic foci, and tumors. Both compounds exerted protective effects on lipid peroxidation, necrosis, cell proliferation, p65 activation, and preneoplastic lesions. Rats under a carcinogenic protocol showed a 52, 71.74, and 51.6% decrease in the number of preneoplastic nodules when pretreated with CAPE, LQM706, and LQM717, respectively. At 12 months after carcinogenic treatment, eight of eight rats developed liver cancer, whereas in the group of rats that received pretreatment with CAPE, LQM706, or LQM717, 62.5, 83.3, or 42.85%, respectively, had tumors. In conclusion, LQM717 has the potential to enhance chemoprotection activity much better than CAPE by markedly reducing the formation of liver cancers in this model, and this is a compound that is easy to obtain.

The chemopreventive activity of the butyric acid prodrug tributyrin in experimental rat hepatocarcinogenesis is associated with p53 acetylation and activation of the p53 apoptotic signaling pathway

The reversibility of non-genotoxic phenotypic alterations has been explored in order to develop novel preventive and therapeutic approaches for cancer control. Previously, it has been demonstrated that histone deacetylase (HDAC) inhibitor tributyrin, a butyric acid prodrug, to have chemopreventive effects on rat hepatocarcinogenesis. The goal of this study was to determine molecular mechanisms associated with the chemopreventive activity of tributyrin. Male Wistar rats were allocated randomly to untreated control group and two experimental groups. Rats in the experimental group 1 were treated with maltodextrin (3g/kg body wt), and rats in experimental group 2 were treated with tributyrin (2g/kg body wt) daily for 8 weeks. Two weeks after treatment initiation, rats from experimental groups were subjected to a 'resistant hepatocyte' model of hepatocarcinogenesis. Treatment with tributyrin resulted in lower HDAC activity and Hdac3 and Hdac4 gene expression, and an increase of histone H3 lysine 9 and 18 and histone H4 lysine 16 acetylation as compared with the experimental group 1. In addition to the increase in histone acetylation, tributyrin caused an increase in the acetylation of the nuclear p53 protein. These changes were accompanied by a normalization of the p53-signaling network, particularly by the upregulation of pro-apoptotic genes, and a consequent increase of apoptosis and autophagy in the livers of tributyrin-treated rats. These results indicate that the chemopreventive activity of tributyrin may be related to an increase of histone and p53 acetylation, which could lead to the induction of the p53 apoptotic pathway.

An approach to the study of gene expression in hepatocarcinogenesis initiation

In carcinogenesis, determination of gene and protein expression profiles is important for prevention and treatment. Caffeic acid phenethyl ester (CAPE) in a single dose administered before carcinogenic initiation induced by diethylnitrosamine (DEN) prevents the appearance of preneoplastic lesions. On the basis of this approach, the main purpose of this work was to compare the gene expression profiles induced by DEN or a previously administered single dose of CAPE. Using a modified hepatocarcinogenesis-resistant hepatocyte model, male Fischer-344 rats were administered with one intraperitoneal dose of CAPE (20 mg/kg) 12 hours before DEN administration (200 mg/kg). Livers were removed and processed for microarray analysis and reverse transcription-polymerase chain reaction 12 hours after CAPE dosing and 24 hours after DEN administration with or without CAPE. CAPE alone did not alter the expression profile. DEN treatment modified the expression of 665 genes, and CAPE plus DEN induced changes in 1371 genes. DEN treatment increased the expression of genes associated with oxidative stress such as glutathione reductase, genes involved in cell cycle regulation including p53, and modified cytochrome P450. CAPE plus DEN diminished the expression of cytochrome involved in DEN bioactivation such as CYP2B1 as well as the expression of regulators of oxidative stress such as glutathione reductase, GST-kappa and GST-theta, and cell cycle regulators such as p53. Using CAPE as a tool, we uncovered new approaches for studying the altered expression of reactive genes and identifying proteins that will help to propose well-sustained and concrete hypothesis of DEN mechanism of hepatocarcinogenesis initiation.

Chemopreventive effects of β-ionone and geraniol during rat hepatocarcinogenesis promotion: distinct actions on cell proliferation, apoptosis, HMGCoA reductase, and RhoA

Chemopreventive activities of the dietary isoprenoids β-ionone (βI) and geraniol (GOH) were evaluated during the promotion phase of hepatocarcinogenesis. Over 5 consecutive weeks, rats received daily 16 mg/100 g body weight (b.w.) of βI (βI group), 25 mg/100 g b.w. of GOH (GOH group), or only corn oil (CO group, controls). Compared to the CO group, the following was observed: only the βI group showed a decrease in the mean number of visible hepatocyte nodules (P<.05); βI and GOH groups had reduced mean number of persistent preneoplastic lesions (pPNLs) (P<.05), but no differences regarding number of remodeling PNL (rPNLs) were observed; only the βI group exhibited smaller rPNL size and percentage of liver sections occupied by pPNLs (P<.05), whereas the GOH group displayed a smaller percentage of liver sections occupied by rPNLs (P<.05); a trend was observed in the βI group, which showed reduced cell proliferation of pPNLs (P<.10), and the GOH group had increased apoptosis in pPNLs and rPNLs (P<.05); only the βI group displayed reduced total plasma cholesterol concentrations (P<.05) and increased hepatic 3-hydroxy-3-methylglutaryl coenzyme A (HMGCoA) reductase mRNA levels (P<.05); only the GOH group had lower hepatic membrane RhoA protein levels (P<.05); both the βI- and GOH-treated groups had higher hepatic concentrations of βI and GOH, respectively (P<.05). Given these data, βI and GOH show promising chemopreventive effects during promotion of hepatocarcinogenesis by acting through distinct mechanism of actions: βI may inhibit cell proliferation and modulate HMGCoA reductase, and GOH can induce apoptosis and inhibit RhoA activation.

Dietary antioxidants in the prevention of hepatocarcinogenesis: a review

In this review, the role of dietary antioxidants in the prevention of hepatocarcinogenesis is examined. Both human and animal models are discussed. Vitamin C, vitamin E, and selenium are antioxidants that are essential in the human diet. A number of non-essential chemicals also contain antioxidant activity and are consumed in the human diet, mainly as plants or as supplements, including beta-carotene, ellagic acid, curcumin, lycopene, coenzyme Q(10), epigallocatechin gallate, N-acetyl cysteine, and resveratrol. Although some human and animal studies show protection against carcinogenesis with the consumption of higher amounts of antioxidants, many studies show no effect or an enhancement of carcinogenesis. Because of the conflicting results from these studies, it is difficult to make dietary recommendations as to whether consuming higher amounts of specific antioxidants will decrease the risk of developing hepatocellular carcinoma.

Anti-proliferative effect of extremely low frequency electromagnetic field on preneoplastic lesions formation in the rat liver

Background

Recently, extremely low frequency electromagnetic fields (ELF-EMF) have been studied with great interest due to their possible effects on human health. In this study, we evaluated the effect of 4.5 mT - 120 Hz ELF-EMF on the development of preneoplastic lesions in experimental hepatocarcinogenesis.

Methods

Male Fischer-344 rats were subjected to the modified resistant hepatocyte model and were exposed to 4.5 mT - 120 Hz ELF-EMF. The effects of the ELF-EMF on hepatocarcinogenesis, apoptosis, proliferation and cell cycle progression were evaluated by histochemical, TUNEL assay, caspase 3 levels, immunohistochemical and western blot analyses.

Results

The application of the ELF-EMF resulted in a decrease of more than 50% of the number and the area of γ-glutamyl transpeptidase-positive preneoplastic lesions (P = 0.01 and P = 0.03, respectively) and glutathione S-transferase placental expression (P = 0.01). The number of TUNEL-positive cells and the cleaved caspase 3 levels were unaffected; however, the proliferating cell nuclear antigen, Ki-67, and cyclin D1 expression decreased significantly (P ≤ 0.03), as compared to the sham-exposure group.

Conclusion

The application of 4.5 mT - 120 Hz ELF-EMF inhibits preneoplastic lesions chemically induced in the rat liver through the reduction of cell proliferation, without altering the apoptosis process.

Organization of the lamin scaffold in the internal nuclear matrix of normal and transformed hepatocytes

Nuclear lamins are among the more abundant proteins making up the internal nuclear matrix, but very little is known about their structure in the nucleoplasm. Using immunoelectron microscopy, we demonstrate the organization of lamins in the nuclear matrix isolated from rat hepatocytes for the first time. Lamin epitopes are arrayed both in locally ordered clusters and in quasi-regular rows. Fourier filtering of the images demonstrates that the epitopes are placed at the nodes and halfway between the nodes of square or rhombic lattices that are about 50 nm on each side, as well as along rows at regular approximately 25-nm intervals. In addition, we have compared this structure with that of the internal nuclear matrix isolated from persistent hepatocyte nodules. In transformed hepatocytes, the islands of lamin lattice are lost, and only a partial regularity in the rows of gold particles remains. We suggest that orthogonal lattice assembly might be an intrinsic property of lamin molecules, and that the disassembly may be triggered by simple molecular events such as phosphorylation.

Chemoprevention of rat hepatocarcinogenesis with histone deacetylase inhibitors: efficacy of tributyrin, a butyric acid prodrug

Hepatocellular carcinoma (HCC) ranks in prevalence and mortality among top 10 cancers worldwide. Butyric acid (BA), a member of histone deacetylase inhibitors (HDACi) has been proposed as an anticarcinogenic agent. However, its short half-life is a therapeutical limitation. This problem could be circumvented with tributyrin (TB), a proposed BA prodrug. To investigate TB effectiveness for chemoprevention, rats were treated with the compound during initial phases of "resistant hepatocyte" model of hepatocarcinogenesis, and cellular and molecular parameters were evaluated. TB inhibited (p < 0.05) development of hepatic preneoplastic lesions (PNL) including persistent ones considered HCC progression sites. TB increased (p < 0.05) PNL remodeling, a process whereby they tend to disappear. TB did not inhibit cell proliferation in PNL, but induced (p < 0.05) apoptosis in remodeling ones. Compared to controls, rats treated with TB presented increased (p < 0.05) hepatic levels of BA indicating its effectiveness as a prodrug. Molecular mechanisms of TB-induced hepatocarcinogenesis chemoprevention were investigated. TB increased (p < 0.05) hepatic nuclear histone H3K9 hyperacetylation specifically in PNL and p21 protein expression, which could be associated with inhibitory HDAC effects. Moreover, it reduced (p < 0.05) the frequency of persistent PNL with aberrant cytoplasmic p53 accumulation, an alteration associated with increased malignancy. Original data observed in our study support the effectiveness of TB as a prodrug of BA and as an HDACi in hepatocarcinogenesis chemoprevention. Besides histone acetylation and p21 restored expression, molecular mechanisms involved with TB anticarcinogenic actions could also be related to modulation of p53 pathways.

Tumor promoting and co-carcinogenic effects in medium-term rat hepatocarcinogenesis are not modified by co-administration of 12 pesticides in mixture at acceptable daily intake

The purpose of this investigation was to evaluate the possible influence of a mixture of pesticides on medium-term carcinogenesis using improved hepatocarcinogenesis protocols. We performed a 12 commercially available pesticides combination with alachlor, atrazine, carbofuran, chlorpyrifos, diazinon, dicofol, endosulfan, iprodione, mancozeb, maneb, procymidone and rotenone. The mixture was given at 1-fold and 10-fold the acceptable daily intake (ADI) level in a set of Solt-Farber-derived protocols involving diethylnitrosamine, 2-acetylaminofluorene treatments and a partial hepatectomy. Co-carcinogenic effect and promoting activity were evaluated using gamma-glutamyl transpeptidase (GGT) positive altered hepatocyte foci, as well, protein and mRNA levels of glutathione S-transferase P (GSTP) in liver extracts as molecular biomarkers of carcinogenic effects. The pesticide treatments when compared to vehicle treatments always produced the same number of hepatocyte lesions and an equal GSTP expression on liver extracts independently of carcinogenic-protocol utilized. On this base, we concluded that the pesticide mixture evaluated in this report does not have tumor promoting activity or co-carcinogenic effect in the rat medium-term liver carcinogenesis. Altogether these data contribute to the confidence that the ADI represents a safe intake level to mixture of pesticides at dietary exposure.

Proteomic analysis of the nuclear matrix in the early stages of rat liver carcinogenesis: identification of differentially expressed and MAR-binding proteins

Tumor progression is characterized by definite changes in the protein composition of the nuclear matrix (NM). The interactions of chromatin with the NM occur via specific DNA sequences called MARs (matrix attachment regions). In the present study, we applied a proteomic approach along with a Southwestern assay to detect both differentially expressed and MAR-binding NM proteins, in persistent hepatocyte nodules (PHN) in respect with normal hepatocytes (NH). In PHN, the NM undergoes changes both in morphology and in protein composition. We detected over 500 protein spots in each two dimensional map and 44 spots were identified. Twenty-three proteins were differentially expressed; among these, 15 spots were under-expressed and 8 spots were over-expressed in PHN compared to NH. These changes were synchronous with several modifications in both NM morphology and the ability of NM proteins to bind nuclear RNA and/or DNA containing MARs sequences. In PHN, we observed a general decrease in the expression of the basic proteins that bound nuclear RNA and the over-expression of two species of Mw 135 kDa and 81 kDa and pI 6.7-7.0 and 6.2-7.4, respectively, which exclusively bind to MARs. These results suggest that the deregulated expression of these species might be related to large-scale chromatin reorganization observed in the process of carcinogenesis by modulating the interaction between MARs and the scaffold structure.

Aqueous crude extract of Rhoeo discolor, a Mexican medicinal plant, decreases the formation of liver preneoplastic foci in rats

There are many plants in Mexico with medicinal properties, some of them used in alternative medicine to treat cancer, such is the case of Rhoeo discolor L. Hér Hance (Commelinaceae family); however, there are not scientific reports that validate their antitumoral property. The present study shows the protective effects of the Rhoeo discolor aqueous crude extract (ACE) against rat liver cancer using the resistant-hepatocyte model. The carcinogenesis protocol consisted on the initiation with N-diethylnitrosamine, followed by the promotion with 2-acetylaminofluorene and a partial hepatectomy. After 24 days, the gamma-glutamyl transpeptidase positive, corresponding to altered hepatocytes foci (AHF), were quantified. Additionally to discard a possible carcinogenic effect of ACE, it was first tested as promoting agent instead 2-acetylaminofluorene, and second, ACE was administered as initiator and promoter instead of the whole carcinogenic treatment. In summary, firstly, ACE administration reduced the number and area of preneoplastic lesions with dose below 20mg/kg body weight and secondly, ACE administration neither presented a promoting or initiator effects nor induced the development of AHF. Results of this investigation justify continuing with further studies of Rhoeo discolor components to develop chemoprevention strategies as an option in the treatment of cancer.

Chronic ethanol intake promotes double gluthatione S-transferase/transforming growth factor-alpha-positive hepatocellular lesions in male Wistar rats

The chronic ethanol intake influence on the gluthatione S-transferase (GST-P) and transforming growth factor alpha (TGF-alpha) expression in remodeling/persistent preneoplastic lesions (PNLs) was evaluated in the resistant hepatocyte model. Male Wistar rats were allocated into five groups: G1, non-treated, fed water and chow ad libitum; G2, non-treated and pair-fed chow (restricted to match that of G3 group) and a maltodextrin (MD) solution in tap water (matched ethanol-derived calories); G3, fed 5% ethanol in drinking water and chow ad libitum; G4, diethylnitrosamine (DEN, 200 mg/kg, body weight) plus 200 parts per million of 2-acetylaminofluorene (2-AAF) for 3 weeks and pair-fed chow (restricted to match that of G5 group) and an MD solution in tap water (matched ethanol-derived calories); G5, DEN/2-AAF treatment, fed ethanol 5% and chow ad libitum. All animals were subjected to 70% partial hepatectomy at week 3 and sacrificed at weeks 12 or 22, respectively. Liver samples were collected for histological analysis or immunohistochemical expression of GST-P, TGF-alpha and proliferating cell nuclear antigen or zymography for matrix metalloproteinases-2 and -9. At the end of ethanol treatment, there was a significant increase in the percentage of liver area occupied by persistent GST-P-positive PNLs, the number of TGF-alpha-positive PNLs and the development of liver tumors in ethanol-fed and DEN/2-AAF-treated groups (G5 versus G4, P < 0.001). In addition, ethanol feeding led to a significant increase in cell proliferation mainly in remodeling and persistent PNLs with immunoreactivity for TGF-alpha at week 22 (P < 0.001). Gelatinase activities were not altered by ethanol treatment. The results demonstrated that ethanol enhances the selective growth of PNL with double expression of TGF-alpha and GST-P markers.

Persistent and remodeling hepatic preneoplastic lesions present differences in cell proliferation and apoptosis, as well as in p53, Bcl-2 and NF-κB pathways

During rat hepatocarcinogenesis preneoplastic lesions (PNL) emerge which may persist (pPNL) and be sites of progress to cancer or suffer remodeling (rPNL) tending to disappear. Cellular and molecular mechanisms involved in both phenotypes are not sufficiently elucidated. pPNL and rPNL cellular proliferation and apoptosis were evaluated in rats submitted to the resistant hepatocyte (RH) model, and an adjusted growth index (AGI) was established. p53, Bcl-2, and NF-kappaB p65 subunit expression was evaluated by immunohistochemistry in pPNL and rPNL. p65 expression and NF-kappaB activation was evaluated by Western blot assays in whole livers. A lower number of BrdU-stained hepatocyte nuclei/mm(2) and higher number of apoptotic bodies (AB) per mm(2) were observed in remodeling compared to pPNL. Cytoplasmic p53 accumulation is related to increased hepatocarcinoma malignancy. We observed that 71.3% pPNL and 25.4% rPNL (P < 0.05) presented p53 staining in the cytoplasm. Similarly, 67.7% pPNL and 23.1 % rPNL (P < 0.05) presented increased Bcl-2 staining. Thirty-two percent pPNL and 15.6% rPNL (P < 0.05) presented p65 staining. Compared to normal rats, increase (P < 0.05) of hepatic p65 expression and NF-kappaB activation in rats submitted to the RH model was observed. In agreement to previous studies hepatic pPNL and rPNL differ regarding cell proliferation and apoptosis. Moreover, persistence and remodeling involve differences in p53, Bcl-2, and NF-kappaB pathways. These data point to molecular pathways that may direct preneoplastic lesions to spontaneously regress or to progress to cancer. J. Cell. Biochem. 103: 538-546, 2008. (c) 2007 Wiley-Liss, Inc.

Lutein presents suppressing but not blocking chemopreventive activity during diethylnitrosamine-induced hepatocarcinogenesis and this involves inhibition of DNA damage

Cancer chemopreventive agents are classified as blocking or suppressing agents if they inhibit initiation or promotion/progression phase of carcinogenesis, respectively. Two experiments were conducted in order to classify lutein as a blocking and/or suppressing agent during rat hepatocarcinogenesis. Inhibitory effects of lutein on hepatic preneoplastic lesions (PNL) and DNA strand breakage induced in Wistar rats by the resistant hepatocyte model of hepatocarcinogenesis (initiation with diethylnitrosamine and promotion with 2-acetylaminofluorene coupled with partial hepatectomy) were investigated when the carotenoid was administered specifically during initiation (experiment 1) or promotion (experiment 2) phase. Animals received by gavage during 2 (experiment 1) or six (experiment 2) consecutive weeks on alternate days 70 mg/kg body weight of lutein. Rats treated with only corn oil during these same periods and submitted to this model were used as controls. Treatment with lutein during initiation did not inhibit nor induced (P>0.05) hepatic preneoplastic lesions and DNA damage. On the other hand, treatment during promotion inhibited (P<0.05) the size of hepatic macroscopic nodules and DNA damage and increased (P<0.05) lutein hepatic levels that reached levels seen in human liver samples. Lutein presented inhibitory actions during promotion but not initiation of hepatocarcinogenesis, being classified as a suppressing agent. This reinforces lutein as a potential agent for liver cancer chemoprevention.

Co-carcinogenic effect of cyclohexanol on the development of preneoplastic lesions in a rat hepatocarcinogenesis model

Cyclohexanol is a basic industrial chemical widely used because of its versatility as an industrial solvent. No studies have been conducted to evaluate the carcinogenic/co-carcinogenic hazards associated with cyclohexanol exposure. In male Fisher 344 rats liver preneoplastic lesions were induced by N-nitrosodiethylamine (150 mg/Kg) i.p., followed by the tumor promoter 2-acetylaminofluorene (2-AAF: 20 mg/kg) orally administered on three consecutive days before partial hepatectomy. The cyclohexanol administration in this hepatocarcinogenesis assay revealed that it has a strong tumor co-promoter potential. There is clear evidence that oxidative stress and the CYP2E1 are components of carcinogenesis. Although no changes in the lipid peroxidation levels were observed between treated and untreated animals, a significant increase in CYP2E1 expression was observed when cyclohexanol was administered 24 h after the last 2-AAF dose. On the other hand, levels of the proliferation markers PCNA and Ki-67 were not increased after treatment with cyclohexanol, but a marked downregulation of the Bax proapoptotic protein was found exclusively in mitochondrial extracts of animals treated with cyclohexanol. This study represents the first report of the ability of cyclohexanol-induced lesions, when administered simultaneously with 2-AAF, to potentiate the development of preneoplastic liver.

A single dose of caffeic acid phenethyl ester prevents initiation in a medium-term rat hepatocarcinogenesis model

AIM: To study of the effect of caffeic acid phenethyl ester (CAPE) on the initiation period in a medium-term assay of hepatocarcinogenesis.

METHODS: Male Wistar rats were subjected to a carcinogenic treatment (CT) and sacrificed at 25^th d; altered hepatic foci (AHF) were generated efficiently. To a second group of rats a single 20 mg/kg doses of CAPE was given 12 h before initiation with CT and were sacrificed at 25^th d. We evaluated the expression of preneoplastic markers as γ-glutamyltranspeptidase (GGT) and glutathione S-transferase type pi protein (GSTp) by histochemistry, RT-PCR and Western blot analyses, respectively. We measured thiobarbituric acid reactive substances (TBARS) in homogenates of liver and used Unscheduled DNA Synthesis (UDS) assay by incorporation of [³H] thymidine (³HdT) in primary hepatocyte cultures (PHC).

RESULTS: At 25^th d after CT CAPE reduced the observed increase of GGT⁺AHF by 84% and liver expression of ggt mRNA by 100%. In case of the GSTp protein, the level was reduced by 90%. As indicative of oxidative stress generated by diethylnitrosamine (DEN) 12 h after its administration, we detected a 68% increase of TBARS. When CAPE was administered before DEN, it completely protected from liver TBARS induction. To have an indication of the sole effect of CAPE on initiation, two carcinogens were tested in a UDS assay in PHC, we used methyl-n-nitrosoguanidine as a direct carcinogen and DEN, as indirect carcinogen. In this assay, genotoxic damage caused by carcinogens was abolished at 5μM CAPE concentration.

CONCLUSION: Our results demonstrated that CAPE possesses anti-genotoxic and antineoplastic capabilities, by an anti-oxidative and free-radical scavenging mechanism.

Celecoxib, a cyclooxygenase-2 inhibitor, prevents induction of liver preneoplastic lesions in rats

BACKGROUND/AIMS

Several studies suggest that cyclooxygenase-2 (COX-2) inhibitors are chemopreventive agents against colon, breast and skin cancer. In this study, we evaluated the chemopreventive effect of celecoxib, a specific COX-2 inhibitor, on the development of liver preneoplastic lesions in rats.

METHODS

Male Sprague-Dawley rats were fed during 5 weeks either a control or an experimental diet containing 1500 ppm celecoxib on a medium-term hepatocarcinogenesis protocol. Livers were collected and evaluated by histological and biochemical assays.

RESULTS

A reduction by 80 and 90% both in the number and size of altered hepatic foci was observed in the group treated with celecoxib during hepatocarcinogenesis treatment, respectively. No evidence of apoptosis was observed in our present study, however, the expression of the proliferation markers such as PCNA and Ki-67 was drastically reduced. Interestingly, neither COX-2 expression nor prostaglandin-E2 (PGE2) production were altered by the hepatocarcinogenic treatment or celecoxib treatment. Finally, celecoxib inhibited the translocation of Rel A/p65 to the nucleus with significant effect on stability of the repressor IkappaB-alpha.

CONCLUSIONS

This is the first demonstration that a specific COX-2 inhibitor, celecoxib, possesses striking chemopreventive activity, inhibiting preneoplastic lesions during hepatocarcinogenesis in vivo, suggesting that celecoxib effects are mediated by PGE2-independent mechanisms.

Squalene does not exhibit a chemopreventive activity and increases plasma cholesterol in a Wistar rat hepatocarcinogenesis model

The eventual chemopreventive effect of squalene (SQ), a triterpene present in olive oil, was evaluated when administered to Wistar rats during a period comprising the initiation and selection/promotion of the "resistant hepatocyte" (RH) model of hepatocarcinogenesis. During 8 consecutive wk, animals received by gavage SQ (100 or 150 mg/100 g body weight) dissolved in corn oil (CO) daily. Animals treated with only CO and submitted to the RH model were used as controls. Treatments with SQ did not result in inhibition of macroscopically visible hepatocyte nodules (P > 0.05) or of hepatic placental glutathione S-transferase- positive preneoplastic lesions (PNL; P > 0.05). Hepatic cell proliferation and apoptosis indexes were not different (P > 0.05) among the different experimental groups, both regarding PNL and surrounding normal tissue areas. There were no significant differences (P > 0.05) among comets presented by rats treated with the two SQ doses or with CO. On the other hand, SQ increased total plasma cholesterol levels when administered at both doses (P < 0.05). This indicates that the isoprenoid was absorbed. Thus, SQ did not present chemopreventive activity during hepatocarcinogenesis and had a hypercholesterolemic effect, suggesting caution when considering its use in chemoprevention of cancer.

Oxidative stress in carcinogenesis. Correlation between lipid peroxidation and induction of preneoplastic lesions in rat hepatocarcinogenesis

Oxidative stress during carcinogen metabolism seems to participate in liver tumor production in the rat. N-diethylnitrosamine is an important carcinogen used in liver cancer animal models. This indirect alkylating agent produces DNA-ethyl adducts and oxidative stress. In contrast, N-ethyl-N-nitrosourea, a direct mutagen, which generates DNA-ethyl adducts, does not produce liver tumors in rat unless it is given under oxidative stress conditions such as partial hepatectomy or phenobarbital treatment. To gain insight into the relation between oxidative stress and hepatocarcinogenicity, the induction of preneoplastic liver lesions was compared among three different initiation protocols related to the initiation-promotion-resistant hepatocyte model. In addition, liver lipid peroxidation levels, determined as thiobarituric acid reactive substances were studied early during the initiation stage. Rats initiated with N-ethyl-N-nitrosourea, 25 days after treatment developed fewer and smaller gamma-glutamyl transpeptidase positive preneoplastic lesions than rats initiated with N-diethylnitrosamine. A pre-treatment with the antioxidant quercetin 1 h before N-diethylnitrosamine initiation, significantly prevented development of gamma-glutamyl transpeptidase-positive lesions. Increased lipid peroxidation levels were induced with N-diethylnitrosamine from 3 to 24 h after initiation, while N-ethyl-N-nitrosourea did not induce increments, and importantly, pre-treatment with quercetin decreased lipid peroxidation induced by N-diethylnitrosamine. These results show correlation between lipid peroxidation and hepatocarcinogenicity and support the important role of oxidative stress on liver carcinogenesis.

Inhibition of liver carcinogenesis in Wistar rats by consumption of an aqueous extract from leaves of Ardisia compressa

This study evaluates the chemopreventive effect of an aqueous extract of dried leaves of Ardisia compressa against liver cancer. A rat liver assay that mimics progressive forms of human disease was used as a carcinogenesis model. Forty-five male Wistar rats (180-200 g body weight) were injected intraperitoneally on day 1 with a single dose (100 mg/kg) of diethylnitrosamine (DEN), and also received via gavage 20 mg/kg acetylaminofluorene (2-AAF), on days 7, 8 and 9. The rats were randomly divided into four groups (n=15). Control groups (Group 1 and Group 2) had free access to water. Group 3 received 0.5% (w/v) of A. compressa tea for 10 days before treatment and during the study as the sole source of fluid until the rats were killed. A fourth group of 15 rats received no carcinogen or promoter but did receive 0.5%, (w/v) of A. compressa tea. All animals had 70% partial hepatectomy at day 10. The incidences of hepatocellular foci, nodules and carcinoma were significantly smaller in Group 3 than in Group 2 (P<0.01). A. compressa tea consumption alone (Group 4) did not induce the development of foci, nodules or carcinomas (P<0.01). The striking observation of this study was that consumption of A. compressa tea resulted in complete inhibition of the chemically-induced hepatocarcinogenesis in Wistar rats.

Chemoprotective effect of caffeic acid phenethyl ester on promotion in a medium-term rat hepatocarcinogenesis assay

Caffeic acid phenethyl ester (CAPE), a natural honeybee product exhibits a spectrum of biological activities including anti-microbial, anti-inflammatory, antioxidant and anti-tumoral actions. CAPE is also chemopreventive against intestinal, colon and skin cancer. Our aim was to extend the study of its chemoprotective features to the promotion of hepatocarcinogenesis. Male Wistar rats were subjected to a protocol under a modified promotion regimen of the resistant hepatocyte model. The altered hepatic foci (AHF) were quantitatively analyzed by histochemistry and image processing. When given during promotion, CAPE (20 mg/kg) decreased the expression of number and area gamma-glutamyl transpeptidase (GGT) positive AHF by 91% and 97%, respectively. When GGT expression was analyzed by RT-PCR, CAPE drastically decreased and prevented expression of almost all GGT transcripts at this stage of the carcinogenic process. Glutathione S-transferase placental form (GST-P), another protein marker for preneoplastic lesions was measured by Western blot and a decrease of 82% was observed. Additionally, we evaluated the effect of CAPE on the expression of nuclear factor NF-kappaB and found an 85% decrease in nuclear localization of the p65 subunit of NF-kappaB; however, their repressor, IkappaBalpha was not modified. Our results showed that CAPE given during promotion in hepatocarcinogenesis protects against induction of GGT-positive AHF, GST-P protein, GGT mRNA expression and translocation of p65. This phenomenon was independent of IkappaBalpha degradation.

Inhibitory effects of beta-carotene and vitamin a during the progression phase of hepatocarcinogenesis involve inhibition of cell proliferation but not alterations in DNA methylation

The inhibitory effects of Beta-carotene and vitamin A administered to rats in the progression phase of the resistant hepatocyte model of hepatocarcinogenesis were investigated. Beta-Carotene- and vitamin A-treated animals tended to present with a lower incidence of hepatic cancers than controls at sacrifice. Vitamin A, but not Beta-carotene, administration also tended to reduce the total number of persistent hepatocyte nodules. Histological examination of sections stained with hematoxylin and eosin confirmed these results. This suggests that both compounds exhibit inhibitory effects during conversion of persistent nodules to cancers, whereas only the retinoid is also capable of inhibiting the evolution of persistent nodules or causing them to regress. Moreover, Beta-carotene- and vitamin A-treated animals showed lower hepatic bromodeoxyuridine labeling indexes in neoplastic lesions as well as in adjacent normal tissues than controls, suggesting an inhibitory action of these substances on cell proliferation. However, neither Beta-carotene nor vitamin A administration resulted in substantial alterations in the CCGG sequence methylation pattern of hydroxymethylglutaryl coenzyme A reductase, c-myc, and c-Ha-ras genes, the products of which are related to cell proliferation and carcinogenesis. Therefore, these inhibitory effects of Beta-carotene and vitamin A on progression of hepatocarcinogenesis do not seem to be related to DNA methylation.

Polychlorinated biphenyls as initiators in liver carcinogenesis: resistant hepatocyte model

A modified Solt-Farber protocol was established to investigate the potential initiating activity of lower chlorinated polychlorinated biphenyl (PCB) congeners in rat liver. Two different studies were conducted in male Fisher 344 rats. PCBs investigated were PCB3, PCB12, PCB38, and PCB77 in study 1 and PCB15, PCB52, PCB77, and the combination of PCB52 and PCB77 in study 2. Rats were subjected to partial hepatectomy followed by a single dose of the suspected initiating agent, diethylnitrosamine, or vehicle. Two weeks later all groups received selection treatment consisting of three daily doses of 2-acetylaminofluorene (2-AAF) and then a single dose of carbon tetrachloride, followed by three additional daily treatments of 2-AAF via gavage. Rats were killed 2 weeks after the last treatment of 2-AAF, and the number and volume of gamma-glutamyltranspeptidase (GGT)-positive foci were determined. Among the PCBs tested, PCB3, PCB15, PCB52, and PCB77 significantly increased the number of GGT-positive foci per cm(3) of liver and per liver. Only PCB3 and PCB15 increased the volume fraction of GGT-positive foci. Histopathologic analysis of hematoxylin- and eosin-stained liver sections showed that rats with significantly increased GGT-positive foci also had extensive cellular alteration. This effect was not seen in nonselection groups. We conclude that, under the conditions and time courses of these experiments, several PCBs have initiating activity in male Fischer 344 rats.

Vitamin A and all-trans and 9-cis retinoic acids inhibit cell proliferation during the progression phase of hepatocarcinogenesis in Wistar rats

The effects of vitamin A and all-trans and 9-cis retinoic acids on the progression phase of hepatocarcinogenesis were evaluated in this study. For this purpose, male Wistar rats were first submitted to the resistant hepatocyte model of carcinogenesis (diethylnitrosamine for initiation and 2-acetylaminofluorene for selection/promotion). Ten months after initiation, the animals were distributed into four groups and treated by gavage, every other day and during eight weeks, with corn oil (control group), vitamin A (10 mg/kg of body wt), all-trans retinoic acid (10 mg/kg body wt), or 9-cis retinoic acid (10 mg/kg body wt). After this period, the animals were killed one hour after intraperitoneal administration of 5-bromo-2-deoxyuridine (BrdU, 100 mg/kg body wt). At the time of sacrifice, liver samples were collected for histopathological (hematoxylin-eosin) examination and immunohistochemical detection of glutathione S-transferase and BrdU, as well as for analysis of retinol and retinoic acid concentrations. Histopathological examination showed the lowest incidence of hepatocarcinomas in vitamin A-treated animals. Moreover, groups treated with retinoids demonstrated lower hepatic BrdU labeling indexes in the neoplastic lesions, as well as in their respective surrounding tissues, than controls. Thus vitamin A and all-trans and 9-cis retinoic acid strongly inhibited cell proliferation when administered during the progression phase of hepatocarcinogenesis. Therefore, the anticarcinogenic effects that have been attributed to these retinoids could be partially related to their capacity of inhibiting in vivo cell proliferation.

Interaction of fumonisin B(1) and aflatoxin B(1) in a short-term carcinogenesis model in rat liver

The co-existence of the fumonisin and aflatoxin mycotoxins in corn merited studies to investigate their possible synergistic toxicological and carcinogenic effects. When utilising a short-term carcinogenesis model in rat liver, both the compounds exhibited slow cancer initiating potency as monitored by the induction of foci and nodules stained positively for the placental form of gluthatione-S-transferase (GSTP(+)). However, when rats were treated in a sequential manner with AFB(1) and FB(1) the number and size of GSTP(+) lesions significantly increased as compared to the separate treatments. Histopathological analyses indicated that the individual treatments showed far less toxic effects, including occasional hepatocytes with dysplastic nuclei, oval cell proliferation and, in the case of FB(1), a few apoptotic bodies in the central vein regions. The sequential treatment regimen induced numerous foci and dysplastic hepatocyte nodules, and with oval cells extending from the periportal regions into the centrilobular regions. This would imply that, in addition to the cancer promoting activity of FB(1) of AFB(1)-initiated hepatocytes, the AFB(1) pre-treatment enhanced the FB(1) initiating potency, presumably by rendering the liver more susceptible to the toxic effects of FB(1). The co-occurrence of AFB(1) and FB(1) in corn consumed as a staple diet could pose an increased risk and should be included in establishing risk assessment parameters in humans.

Effects of beta-carotene and vitamin A on oval cell proliferation and connexin 43 expression during hepatic differentiation in the rat(1)

The effects of beta-carotene and vitamin A administrations were evaluated in an in vivo model of hepatic cell differentiation. For this purpose, male Wistar rats received beta-carotene (70 mg/kg of body weight), vitamin A (10 mg/kg of body weight) or corn oil (control group), by gavage and at every other day during the entire experimental period. After 4 consecutive weeks of treatment, the animals were submitted to the AAF/PH model of hepatic cell differentiation (6 x 20 mg of AAF [2-acetylaminofluorene]/kg of body weight and partial hepatectomy) and killed on different days following the surgery (until day 16 after hepatectomy). Liver samples were collected for determination of beta-carotene, retinol and retinyl palmitate concentrations, for histopathological (hematoxilin-eosin) examination, for immunohistochemical detection of glutathione S-transferase, as well as for the evaluation of connexin 43 (a structural protein of gap junctions of oval cells) expression by northern blot analysis. Compared to controls, the oval cell proliferation peaks (observed by histopathological examination and immunohistochemistry) and connexin 43 expression peaks, were postponed to later days after hepatectomy, in a similar way in beta-carotene and vitamin A treated animals. Compared to the other experimental groups, the vitamin A treated group showed an increase in connexin 43 expression. It was concluded that beta-carotene and vitamin A modulated oval cell proliferation and connexin 43 expression, delaying both events. These findings suggest that beta-carotene and vitamin A can modulate the hepatic differentiation process in vivo.

Inheritance of resistance to promotion of preneoplastic liver lesions in Copenhagen rats

Previously, we have shown that Copenhagen (Cop) rats are highly resistant to the induction of putative preneoplastic, glutathione S-transferase 7-7- (GST 7-7) positive liver lesions following treatment with a modified resistant hepatocyte (RH) protocol. The objective of this study was to determine if resistance is inherited in a dominant or recessive manner and to derive an estimate of the number of genetic loci involved. We crossed male and female Cop rats with F344 rats to produce F1 offspring. Backcross rats were generated using female F1 rats and either Cop or F344 males, resulting in B1c and B1f generations, respectively. The male rats from all these crosses were initiated with diethylnitrosamine (200 mg/kg) at 7 to 8 weeks of age and were promoted 3 weeks later with the RH protocol (2-acetylaminofluorene and a two-thirds partial hepatectomy). The rats were sacrificed 3 weeks after the partial hepatectomy and their livers were sectioned and stained for GST 7-7-positive lesions. The susceptibility of F1 rats was in between Cop and F344 rats, having 21.7% +/- 2.0% (mean +/- SEM) of their liver volume occupied by lesions versus 4.2% +/- 0.8% for Cop and 53.0% +/- 5.8% for F344 rats. As expected, B1c rats had a volume of liver occupied by lesions that was in between the F1 and Cop rats at 13.5% +/- 1.6%. Surprisingly, B1f rats were similar to B1c rats in their resistance (9.1% +/- 2.1%). These results point to a complex, polygenic inheritance pattern that can be explained by a minimum of four loci, one of which shows recessive epistasis.

Matrix metalloproteinases-2 and 9 do not play a role in the growth of preneoplastic liver lesions in F344 rats

Matrix metalloproteinases- (MMPs) 2 and 9 (gelatinases A and B) have been implicated in tumor invasion and metastasis, and recent studies have shown increased levels of these enzymes during recovery from partial hepatectomy (PH) in rats. F344 rats are highly susceptible to the growth of glutathione S-transferase 7-7- (GST 7-7) positive preneoplastic liver lesions promoted using the modified resistant hepatocyte (RH) protocol. Since the RH protocol consists of 2-acetylaminofluorene (2-AAF) followed by a PH, we reasoned that MMP-2 and -9 might be critical for the growth of lesions. Using gelatin zymography, we examined the expression of these enzymes in the livers of F344 rats treated with the RH protocol and sacrificed on Days 2, 4, 7, 14, and 21 after 2-AAF/PH. We found increases in both pro- and active MMP-2 and -9 over baseline levels, with the highest levels occurring on Day 7 post-PH. Also, a 54-kDa band, likely to be proMMP-1, was elevated in a pattern similar to MMP-2 and -9. In contrast to F344 rats, identically treated Copenhagen rats that are highly resistant to promotion of liver lesion growth using the RH protocol had significantly lower levels of proMMP-1 and -2. To test the importance of these MMPs to the growth of liver lesions, F344 rats that had been initiated with diethylnitrosamine were treated using the RH protocol. They then received either the MMP inhibitor batimastat (30 mg/kg, intraperitoneally) or vehicle alone daily from Day 3 to 20 post-PH and were sacrificed on Day 21. There were no differences in the percentage of liver volume occupied by GST 7-7-positive lesions (19.1 +/- 4.84 vs 19.4 +/- 3.31, treated versus vehicle, mean +/- SEM) or liver weight as a percentage of body weight (4.11% +/- 0.15 vs 4.07% +/- 0.18, treated versus vehicle, mean +/- SEM) between the treated and control groups. Treatment of rats with batimastat clearly did not affect lesion growth or liver regeneration following the RH protocol. These results suggest that increases in gelatinase expression during the RH protocol are a result of the promotional stimulus rather than a mechanism by which 2-AAF/PH causes lesion growth.

A growth-constrained environment drives tumor progression invivo

We recently have shown that selective growth of transplanted normal hepatocytes can be achieved in a setting of cell cycle block of endogenous parenchymal cells. Thus, massive proliferation of donor-derived normal hepatocytes was observed in the liver of rats previously given retrorsine (RS), a naturally occurring alkaloid that blocks proliferation of resident liver cells. In the present study, the fate of nodular hepatocytes transplanted into RS-treated or normal syngeneic recipients was followed. The dipeptidyl peptidase type IV-deficient (DPPIV(-)) rat model for hepatocyte transplantation was used to distinguish donor-derived cells from recipient cells. Hepatocyte nodules were chemically induced in Fischer 344, DPPIV(+) rats; livers were then perfused and larger (>5 mm) nodules were separated from surrounding tissue. Cells isolated from either tissue were then injected into normal or RS-treated DPPIV(-) recipients. One month after transplantation, grossly visible nodules (2--3 mm) were seen in RS-treated recipients transplanted with nodular cells. They grew rapidly, occupying 80--90% of the host liver at 2 months, and progressed to hepatocellular carcinoma within 4 months. By contrast, no liver nodules developed within 6 months when nodular hepatocytes were injected into the liver of recipients not exposed to RS, although small clusters of donor-derived cells were present in these animals. Taken together, these results directly point to a fundamental role played by the host environment in modulating the growth and the progression rate of altered cells during carcinogenesis. In particular, they indicate that conditions associated with growth constraint of the host tissue can drive tumor progression in vivo.

Resistance of Copenhagen rats to hepatocarcinogenesis does not involve T-cell immunity

Previously, we have shown that Copenhagen (Cop) rats are highly resistant, compared with susceptible F344 rats, to the growth of glutathione S-transferase 7-7 (GST 7-7) positive preneoplastic liver lesions following treatment with a modified resistant hepatocyte (RH) protocol. Donryu rats, a strain with a level of susceptibility similar to F344, have a reduced T-cell response compared with the closely related, but highly resistant, DRH rat. Cop and DRH rats share several characteristics in their resistance to preneoplastic liver lesion growth and this study, therefore, was designed to examine whether T-cells play a role in Cop resistance. Cop rats were crossed with an athymic (nude) rat to produce F1s that were then interbred to produce F2 animals, some of which were nude with a partial Cop background. A comparison of the susceptibility of nude F2 animals and their euthymic (non-nude) littermates allowed us to determine what role, if any, T-cells play in Cop resistance. We treated 11 Cop, 11 F344, 19 nude F2s, and 18 non-nude F2s with diethylnitrosamine (DEN), followed 3 weeks later by a modified RH protocol. As expected, F344 rats were highly susceptible, having 41.9 +/- 3.3% (mean +/- SEM) of their liver section areas occupied by GST 7-7-positive lesions and Cop rats were highly resistant, having only 4.7 +/- 1.1% of their liver section areas occupied by lesions. Both nude and non-nude F2s were, like Cop rats, highly resistant (1.8 +/- 0.29 and 2.7 +/- 0.45%, respectively). These results show that T-cells are unnecessary for Cop rat resistance, or only play a minor role, and that the nude parental strain is also likely to be resistant to the growth of preneoplastic liver lesions.

The slow induction of resistant hepatocytes during initiation of hepatocarcinogenesis by the nongenotoxic carcinogen clofibrate

This study was designed to explore whether a well-known nongenotoxic liver carcinogen, clofibrate, would induce rare resistant hepatocytes similar to those seen during initiation of hepatocarcinogenesis with many genotoxic carcinogens. Male young adult F344 rats were exposed to a control diet containing 0.5% (w/w) clofibrate for 3, 6, or 10 months. After 1 month on a diet free of clofibrate, the animals were assayed for resistant hepatocytes by a standardized selection procedure using 2-acetylaminofluorene as the inhibitor and partial hepatectomy as a strong stimulus for cell proliferation. No resistant hepatocytes were found in the animals exposed to clofibrate for 3 months or in any of a series of control animals. However, animals on the clofibrate for 6 and 10 months contained resistant hepatocytes that were clonally expanded to produce hepatocyte nodules. These nodules were indistinguishable on gross and microscopic examination from hepatocyte nodules seen in animals in which nodules are induced with one of many different genotoxic carcinogens. Also, like those nodules, the nodules seen in the animals exposed to clofibrate stained positively for glutathione S-transferase 1-1 and gamma-glutamyl transpeptidase and negatively for ATPase. The evidence from this study indicates that the nongenotoxic carcinogen, clofibrate, induces early cellular changes in the liver that are very similar to those induced by many different genotoxic carcinogens. These changes are manifest as a resistance phenotype in a few scattered hepatocytes that now can be clonally expanded selectively to form hepatocyte nodules. However, the resistant hepatocytes are induced by clofibrate much more slowly. Whether this basic similarity pertains to the later steps in the hepatocarcinogenic process remains to be studied.

Effect of fasting/refeeding on the incidence of chemically induced hepatocellular carcinoma in the rat

Caloric restriction has been associated with a delay in the development of both spontaneous and induced neoplasia. In contrast, cycles of fasting/refeeding were shown by us and others to enhance the incidence of early lesions during chemical carcinogenesis in rat liver. The present, long-term study was undertaken to establish whether such a diffential effect would also extend to the later phases of cancer development, until the overt appearance of neoplasia. Male Fischer 344 rats were initiated with a single dose of diethylnitrosamine (DENA, 200 mg/kg i.p.) and starting 1 week later they were either exposed to three cycles of fasting (3 days) followed by refeeding (11 days) or were fed continuously. Seven weeks after DENA administration the rats were exposed to the resistant hepatocyte model of the liver tumor promotion protocol. All animals were killed 1 year after initiation. Incidence of hepatocellular carcinoma was 2-fold higher in the fasted/refed group compared with the controls (72 versus 36%). In addition, cancers were also larger and of higher histological grade in the former group, with one animal showing metastases to the lungs, while no metastases developed in control animals. Fasting caused a decrease in total liver DNA (from 25.2 +/- 1.1 to 16.5 +/- 1.1 mg after 3 days) which was associated with a decrease in hepatocyte labeling index and mitotic activity and high levels of single cell death (apoptosis). In contrast, a sharp increase in hepatocyte proliferation was observed on day 2 of refeeding and this was more pronounced in glutathione S-transferase 7-7 positive foci compared with surrounding liver (10.2 +/- 2.3 versus 4.6 +/- 0.8%). Such a proliferative wave was associated with a sharp decline in the incidence of cell death. It is concluded that fasting/refeeding performed early after initiation accelerates the development of chemically induced hepatocellular carcinoma in the rat.

The effect of butylated hydroxytoluene on selected immune surveillance parameters in rats bearing enzyme-altered hepatic preneoplastic lesions

Selected immune function parameters were examined in male Fischer 344 rats following (a) induction of enzyme-altered preneoplastic liver foci (EAF), and (b) growth modulation of EAF by 30-day feeding with the food antioxidant butylated hydroxytoluene (BHT). Glutathione S-transferase-P (GSTP)-positive EAF were observed in livers of rats receiving diethylnitrosamine (DEN), 2-acetylaminofluorene (2-AAF) and partial hepatectomy (PH) (Solt-Farber procedure), with or without BHT treatment. The induction of EAF and/or 0.5% BHT treatment resulted in a significant reduction in the natural killer (NK) cell activity of splenocytes. PH did not affect NK activity significantly compared with control (no PH) rats. The concanavalin A-induced lymphoproliferative activity of splenocytes was increased in rats with PH compared with those without. A lag in time needed to attain maximum calcium release was observed only in the rats with PH compared with those without PH. None of the treatments affected the phagocytic activity of resident peritoneal macrophages. Only EAF-bearing rats without BHT treatment had increased granulocyte and monocyte levels, while the leucocyte and lymphocyte levels were reduced by the initiator DEN. but not by BHT treatment. Further investigations are necessary to determine whether the observed suppression of NK cell activity during EAF induction and growth modulation by BHT is a contributing factor in enhancement of rodent liver neoplasia by this non-genotoxic food antioxidant.