An integrative analysis of chemically-induced cirrhosis-associated hepatocarcinogenesis: Histological, biochemical and molecular features

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.

Biased Quantification of Rat Liver Fibrosis-Meta-Analysis with Practical Recommendations and Clinical Implications

For liver fibrosis assessment, the liver biopsy is usually stained with Masson's trichrome (MT) or picrosirius red (PSR) to quantify liver connective tissue (LCT) for fibrosis scoring. However, several concerns of such semiquantitative assessments have been raised, and when searching for data on the amount of LCT in healthy rats, the results vastly differ. Regarding the ongoing reproducibility crisis in science, it is necessary to inspect the results and methods, and to design an unbiased and reproducible method of LCT assessment. We searched the Medline database using search terms related to liver fibrosis, LCT and collagen, rat strains, and staining methods. Our search identified 74 eligible rat groups in 57 studies. We found up to 170-fold differences in the amount of LCT among healthy Wistar and Sprague-Dawley rats, with significant differences even within individual studies. Biased sampling and quantification probably caused the observed differences. In addition, we also found incorrect handling of liver fibrosis scoring. Assessment of LCT using stereological sampling methods (such as systematic uniform sampling) would provide us with unbiased data. Such data could eventually be used not only for the objective assessment of liver fibrosis but also for validation of noninvasive methods of the assessment of early stages of liver fibrosis.

Biodistribution Profile of Magnetic Nanoparticles in Cirrhosis-Associated Hepatocarcinogenesis in Rats by AC Biosusceptometry

Since magnetic nanoparticles (MNPs) have been used as multifunctional probes to diagnose and treat liver diseases in recent years, this study aimed to assess how the condition of cirrhosis-associated hepatocarcinogenesis alters the biodistribution of hepatic MNPs. Using a real-time image acquisition approach, the distribution profile of MNPs after intravenous administration was monitored using an AC biosusceptometry (ACB) assay. We assessed the biodistribution profile based on the ACB images obtained through selected regions of interest (ROIs) in the heart and liver position according to the anatomical references previously selected. The signals obtained allowed for the quantification of pharmacokinetic parameters, indicating that the uptake of hepatic MNPs is compromised during liver cirrhosis, since scar tissue reduces blood flow through the liver and slows its processing function. Since liver monocytes/macrophages remained constant during the cirrhotic stage, the increased intrahepatic vascular resistance associated with impaired hepatic sinusoidal circulation was considered the potential reason for the change in the distribution of MNPs.

Selecting an Appropriate Experimental Animal Model for Cholangiocarcinoma Research

Cholangiocarcinoma (CCA) is a highly aggressive biliary tree malignancy with intrahepatic and extra-hepatic subtypes that differ in molecular pathogeneses, epidemiology, clinical manifestations, treatment, and prognosis. The overall prognosis and patient survival remains poor because of lack of early diagnosis and effective treatments. Preclinical in vivo studies have become increasingly paramount as they are helpful not only for the study of the fundamental molecular mechanisms of CCA but also for developing novel and effective therapeutic approaches of this fatal cancer. Recent advancements in cell and molecular biology have made it possible to mimic the pathogenicity of human CCA in chemical-mechanical, infection-induced inflammatory, implantation, and genetically engineered animal models. This review is intended to help investigators understand the particular strengths and weaknesses of the currently used in vivo animal models of human CCA and their related modeling techniques to aid in the selection of the one that is the best for their research needs.

Vitamin D3 supplementation alleviates chemically-induced cirrhosis-associated hepatocarcinogenesis

Vitamin D₃ (VD₃) deficiency has been associated with increased risk for cirrhosis and hepatocellular carcinoma, a highly incident malignant neoplasia worldwide. On the other hand, VD₃ supplementation has shown some beneficial effects in clinical studies and rodent models of chronic liver disease. However, preventive effects of dietary VD₃ supplementation in cirrhosis-associated hepatocarcinogenesis is still unknow. To investigate this purpose, male Wistar rats submitted to a combined diethylnitrosamine- and thioacetamide-induced model were concomitantly supplemented with VD₃ (5,000 and 10,000 IU/kg diet) for 25 weeks. Liver samples were collected for histological, biochemical and molecular analysis. Serum samples were used to measure 25-hydroxyvitamin D [25(OH)D] and alanine aminotransferase levels. Both VD₃ interventions decreased hepatic collagen deposition and pro-inflammatory p65 protein levels, while increased hepatic antioxidant catalase and glutathione peroxidase activities and serum 25(OH)D, without a clear dose-response effect. Nonetheless, only the highest concentration of VD₃ increased hepatic protein levels of VD receptor, while decreased the number of large preneoplastic glutathione-S-transferase- (>0.5 mm²) and keratin 8/18-positive lesions, as well the multiplicity of hepatocellular adenomas. Moreover, this intervention increased hepatic antioxidant Nrf2 protein levels and glutathione-S-transferase activity. In summary, dietary VD₃ supplementation - in special the highest intervention - showed antifibrotic and antineoplastic properties in chemically-induced cirrhosis-associated hepatocarcinogenesis. The positive modulation of Nrf2 antioxidant axis may be mechanistically involved with these beneficial effects, and may guide future clinical studies.

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.

Dual proteotoxic stress accelerates liver injury via activation of p62-Nrf2

Protein accumulation is the hallmark of various neuronal, muscular, and other human disorders. It is also often seen in the liver as a major protein-secretory organ. For example, aggregation of mutated alpha1-antitrypsin (AAT), referred to as PiZ, is a characteristic feature of AAT deficiency, whereas retention of hepatitis B surface protein (HBs) is found in chronic hepatitis B (CHB) infection. We investigated the interaction of both proteotoxic stresses in humans and mice. Animals overexpressing both PiZ and HBs (HBs-PiZ mice) had greater liver injury, steatosis, and fibrosis. Later they exhibited higher hepatocellular carcinoma load and a more aggressive tumor subtype. Although PiZ and HBs displayed differing solubility properties and distinct distribution patterns, HBs-PiZ animals manifested retention of AAT/HBs in the degradatory pathway and a marked accumulation of the autophagy adaptor p62. Isolation of p62-containing particles revealed retained HBs/AAT and the lipophagy adapter perilipin-2. p62 build-up led to activation of the p62-Nrf2 axis and emergence of reactive oxygen species. Our results demonstrate that the simultaneous presence of two prevalent proteotoxic stresses promotes the development of liver injury due to protein retention and activation of the p62-Nrf2 axis. In humans, the PiZ variant was over-represented in CHB patients with advanced liver fibrosis (unadjusted odds ratio = 9.92 [1.15-85.39]). Current siRNA approaches targeting HBs/AAT should be considered for these individuals. © 2021 The Authors. The Journal of Pathology published by John Wiley & Sons, Ltd. on behalf of The Pathological Society of Great Britain and Ireland.

Beneficial effects of anthocyanin-rich peels of Myrtaceae fruits on chemically-induced liver fibrosis and carcinogenesis in mice

Hepatocellular carcinoma (HCC) arising from fibrosis/cirrhosis is the most common type of primary liver cancer. Conversely, a higher intake of fruits and vegetables might play a protective role in HCC risk. Recently, Myrtaceae family tropical fruits have raised great interest due to the high levels of anthocyanins especially in their peels, which are usually discarded upon consumption. Anthocyanins are antioxidant pigments known to have beneficial effects in vivo/in vitro cancer bioassays. Thus, we evaluated whether dietary Myrciaria jaboticaba, Syzygium cumini, and Syzygium malaccense fruit peel powders reduce fibrosis and hepatocarcinogenesis in mice. Female C3H/HeJ mice were submitted to the model of diethylnitrosamine/carbon tetrachloride-induced liver fibrosis and carcinogenesis. Concomitantly, mice received a basal diet containing 2% of M. jaboticaba, S. cumini, or S. malaccense fruit peel powders, obtained by convective drying, for 10 weeks. M. jaboticaba peel powder showed the highest levels of total anthocyanins, while S. cumini peel powder displayed the greatest diversity of these pigments. All Myrtaceae family peel powders reduced the serum levels of the liver injury marker alanine aminotransferase. M. jaboticaba peel feeding reduced the incidence of liver preneoplastic foci, hepatocyte proliferation (Ki-67), and the protein levels of hepato-mitogen tumor necrosis factor-alpha (TNF-α). M. jaboticaba peel feeding also diminished liver lipid peroxidation and increased total glutathione levels. S. cumini peel feeding reduced hepatic collagen, lipid peroxidation, and TNF-α levels while increased catalase activity. Although S. malaccense peel powder, which displayed the lowest anthocyanin levels, decreased oxidative stress, and cytokine levels, no effects were observed on liver fibrosis or preneoplastic lesion outcomes. Findings indicate a protective effect of anthocyanin-rich M. jaboticaba and S. cumini peel powder feeding on preneoplastic lesion development and fibrosis, respectively. Results indicate that differential biological responses may be attributed to distinct anthocyanin profiles and levels, assigning a functional/market value to the underutilized peel fraction.

Therapy of Primary Liver Cancer

Primary liver cancer (PLC) is a fatal disease that affects millions of lives worldwide. PLC is the leading cause of cancer-related deaths and the incidence rate is predicted to rise in the coming decades. PLC can be categorized into three major histological subtypes: hepatocellular carcinoma (HCC), intrahepatic cholangiocarcinoma (ICC), and combined HCC-ICC. These subtypes are distinct with respect to epidemiology, clinicopathological features, genetic alterations, and clinical managements, which are thoroughly summarized in this review. The state of treatment strategies for each subtype, including the currently approved drugs and the potential novel therapies, are also discussed.

The combination of coffee compounds attenuates early fibrosis-associated hepatocarcinogenesis in mice: involvement of miRNA profile modulation

Aberrant microRNA expression implicates on hepatocellular carcinoma (HCC) development. Conversely, coffee consumption reduces by ~40% the risk for fibrosis/cirrhosis and HCC, while decaffeinated coffee does not. It is currently unknown whether these protective effects are related to caffeine (CAF), or to its combination with other common and/or highly bioavailable coffee compounds, such as trigonelline (TRI) and chlorogenic acid (CGA). We evaluated whether CAF individually or combined with TRI and/or CGA alleviates fibrosis-associated hepatocarcinogenesis, examining the involvement of miRNA profile modulation. Then, male C3H/HeJ mice were submitted to a diethylnitrosamine/carbon tetrachloride-induced model. Animals received CAF (50 mg/kg), CAF+TRI (50 and 25 mg/kg), CAF+CGA (50 and 25 mg/kg) or CAF+TRI+CGA (50, 25 and 25 mg/kg), intragastrically, 5×/week, for 10 weeks. Only CAF+TRI+CGA combination reduced the incidence, number and proliferation (Ki-67) of hepatocellular preneoplastic foci while enhanced apoptosis (cleaved caspase-3) in adjacent parenchyma. CAF+TRI+CGA treatment also decreased hepatic oxidative stress and enhanced the antioxidant Nrf2 axis. CAF+TRI+CGA had the most pronounced effects on decreasing hepatic pro-inflammatory IL-17 and NFκB, contributing to reduce CD68-positive macrophage number, stellate cell activation, and collagen deposition. In agreement, CAF+TRI+CGA upregulated tumor suppressors miR-144-3p, miR-376a-3p and antifibrotic miR-15b-5p, frequently deregulated in human HCC. CAF+TRI+CGA reduced the hepatic protein levels of pro-proliferative EGFR (miR-144-3p target), antiapoptotic Bcl-2 family members (miR-15b-5p targets), and the number of PCNA (miR-376a-3p target) positive hepatocytes in preneoplastic foci. Our results suggest that the combination of most common and highly bioavailable coffee compounds, rather than CAF individually, attenuates fibrosis-associated hepatocarcinogenesis by modulating miRNA expression profile.

Protective Effects of Dietary Capsaicin on the Initiation Step of a Two-Stage Hepatocarcinogenesis Rat Model

Capsaicin (CPS), an ingredient of Capsicum plants, has anti-inflammatory, antioxidant and antitumoral properties. The mechanisms of CPS on hepatocarcinogenesis preclinical bioassays are not described. Thus, the protective effects CPS were evaluated in the early stages of chemically-induced hepatocarcinogenesis. Male Wistar rats received diet containing 0.01% or 0.02% CPS for 3 weeks. Afterwards, animals received a dose of hepatocarcinogen diethylnitrosamine (DEN, 100 mg/kg body weight). From weeks 4-12, groups had their diet replaced by a 0.05% phenobarbital supplemented one to promote DEN-induced preneoplastic lesions. Animals were euthanized 24 h after DEN administration (n = 5/group) or at week 12 (n = 9/group). The estimated CPS intake in rats resembled human consumption. At the end of week 3, dietary 0.02% CPS attenuated DEN-induced oxidative damage and, consequently, hepatocyte necrosis by reducing serum alanine aminotransferase levels, liver CD68-positive macrophages, lipid peroxidation, while increasing antioxidant glutathione system. Additionally, 0.02% CPS upregulated vanilloid Trpv1 receptor and anti-inflammatory epoxygenase Cyp2j4 genes in the liver. Ultimately, previous 0.02% CPS intake decreased the number of GST-P-positive preneoplastic lesions at week 12. Thus, CPS attenuated preneoplastic lesion development, primarily by diminishing DEN-induced oxidative liver injury. Findings indicate that CPS is a promising chemopreventive agent when administered after and during the early stages of hepatocarcinogenesis.

Early molecular events associated with liver and colon sub-acute responses to 1,2-dimethylhydrazine: Potential implications on preneoplastic and neoplastic lesion development

This study unveiled the early cellular and molecular events induced by 1,2-dimethylhydrazine (DMH) in the colon and liver and their implications on pre- and neoplastic lesion burden in a late timepoint. Male Wistar rats received four DMH injections (40 mg/kg body weight) for 2 weeks and were sacrificed 24 h (short-term study) or 22 (medium-term study) weeks after the last DMH administration. In the short-term study, DMH led to increased leukocyte (comet assay) and colon (H2AX) genotoxicity, enhanced proliferation (Ki-67) and apoptosis (caspase-3) indexes in both liver and colon. Furthermore, the expression of mRNA (Cat, Gsta1, Gsta2, Gpx1, Gstm1, Sod1, Sod2 and Sod3) and the activity of antioxidant agents were diminished in the colon and liver of DMH-induced rats, eliciting an environment of oxidative stress featuring elevated lipid hydroperoxide levels. Apoptosis effectors were upregulated in the liver (Bax, Casp3 and Fas), and developmental genes were downregulated in both colon and liver (Foxa1, Foxa2, Smad2 and Smad4). In the medium-term study, DMH led to a high number of preneoplastic colonic aberrant crypt foci and tumors (adenomas and invasive adenocarcinomas) but few preneoplastic hepatic glutathione S-transferase (GST-P)-positive foci. Our novel gene expression data highlights overlooked mechanisms in the liver (main metabolizing organ) and colon (main target organ) on toxicity and carcinogenesis induced by repeated doses of DMH, as both organs should be considered in further interventions on the initiation stage of colon carcinogenesis.

Calcitriol Prevents Neuroinflammation and Reduces Blood-Brain Barrier Disruption and Local Macrophage/Microglia Activation

Multiple sclerosis (MS) is a progressive disease of the central nervous system (CNS) that involves damage to the myelin sheath surrounding axons. MS therapy is based on immunomodulatory drugs that reduce disease recurrence and severity. Vitamin D is a hormone whose immunomodulatory ability has been widely demonstrated, including in experimental autoimmune encephalomyelitis (EAE), which is an animal model of CNS inflammation. In this study, we evaluated the potential of very early intervention with the active form of vitamin D (1,25-dihydroxyvitamin D3) to control neuroinflammation during EAE development. EAE was induced in C57BL/6J mice and 1,25-dihydroxyvitamin D3 administration began 1 day after disease induction. This procedure decreased prevalence, clinical score, inflammation, and demyelination. It also reduced MHCII expression in macrophages and microglia as well as the level of oxidative stress and messenger RNA (mRNA) expression for NLRP3, caspase-1, interleukin (IL)-1β, CX₃CR1, CCL17, RORc and Tbx21 at the CNS. Otherwise, mRNA expression for ZO-1 increased at the lumbar spinal cord. These effects were accompanied by the stabilization of blood-spinal cord barrier permeability. The results of this study indicate that early intervention with 1,25-dihydroxyvitamin D3 can control the neuroinflammatory process that is the hallmark of EAE and MS immunopathogenesis and should thus be explored as an adjunct therapy for MS patients.

Endurance training but not high-intensity interval training reduces liver carcinogenesis in mice with hepatocellular carcinogen diethylnitrosamine

Physical activity may reduce cancer initiation. High-intensity interval training (HIT) has been reported to be superior to moderate continuous endurance training (ET) for maximizing health outcomes in cardiovascular disease, obesity and type 2 diabetes. However, the role of HIT vs. ET in the prevention of liver cancer is poorly understood. This study aimed to determine how HIT vs. ET affects cancer initiation in mice with the hepatocellular carcinogen diethylnitrosamine (DEN). C57BL/6 mice were treated with DEN at 3-12 weeks of age and, from 8 to 26 weeks of age, treated with either of exercise modes on treadmill: HIT (85-90% VO2max with intervals) and ET (65-75% VO2max without intervals). We found that mice treated with ET had lower cancer initiation but higher fat mass compared to control DEN-injected mice. In contrast, HIT could not significantly reduce cancer initiation and tumor volumes. Metabolomic analysis in the liver indicated marked differences in cholesterol, palmitic acid, stearic acid, uracil, hydroxypyridine and maltose between HIT- and ET-treated mice, and demonstrated good and obvious separation between ET and DEN control group. Furthermore, mice treated with ET had lower expression of pro-inflammatory cytokines and pro-proliferation genes in liver compared to DEN control group. ET protocol reduced the accumulation of toxic metabolite carbamate, increased the protein level of caspase-1, and reduced JNK phosphorylation in liver. These data indicates that moderate-intensity endurance training may be superior to high-intensity interval training for reducing liver cancer initiation in mice.

Dunaliella salina microalgae oppose thioacetamide-induced hepatic fibrosis in rats

Several hepatic pathological conditions are correlated with the stimulation of hepatic stellate cells. This induces a cascade of events producing accretion of extracellular matrix components triggering fibrosis. Dunaliella salina, rich in carotenoids, was investigated for its potential antagonizing activity; functionally and structurally against thioacetamide (TAA) - induced hepatic fibrosis in rats. Adult male albino Wistar rats were treated with three dose levels of D. salina powder or extract (daily, p.o.); for 6 weeks, concomitantly with TAA injection. Serum levels of aspartate transaminase (AST), alanine transaminase (ALT), alkaline phosphatase (ALP), bilirubin and albumin were determined. Reduced glutathione (GSH), malondialdehyde (MDA), smooth muscle actin alpha (α-SMA) and collagen I hepatic contents were also estimated. Treatment with D. salina powder or extract caused a significant decline in serum levels of AST, ALT, ALP, bilirubin, MDA and hepatic contents of α-SMA and collagen I. Additionally, serum albumin and GSH hepatic content were highly elevated. Liver histopathological examination also indicated that D. salina reduced fibrosis, centrilobular necrosis, and inflammatory cell infiltration evoked by TAA. The results implied that D. salina exerts protective action against TAA-induced hepatic fibrosis in rats. The phytochemical investigation revealed high total carotenoid content prominently β-carotene (15.2 % of the algal extract) as well as unsaturated fatty acids as alpha-linolenic acid which accounts for the hepatoprotective activity.

Resveratrol Reverses Thioacetamide-Induced Renal Assault with respect to Oxidative Stress, Renal Function, DNA Damage, and Cytokine Release in Wistar Rats

Background

Thioacetamide (TAA), a class 2B-type carcinogen, is a potent toxicant. Toxicities caused by this compound in various tissues due to oxidative stress, increase of proinflammatory markers, and apoptosis have been reported; however, reports on kidney toxicity are negligible. Resveratrol (RSV), on the other hand, has demonstrated antioxidant and anti-inflammatory effects in different cases. Resveratrol's protective effects against TAA kidney toxicity were investigated in four rat groups.

Methodology

Four groups of rats were studied as follows (n = 8): control group, where rats were fed normal diet and water; TAA group, where rats received 0.3% TAA in water for two weeks; RSV group, where rats received 10 mg/kg body weight (bw) of RSV as oral suspension for two weeks; and treated group, where rats orally received 10 mg/kg bw RSV and simultaneously received 0.3% TAA for two weeks. Kidney homogenates from all groups were analyzed for cytokine release (IL-4, TNF-α, and IFN-γ) and oxidative stress (lipid peroxidation, catalase, and 8-OHdG). The serum of rats was analyzed for the quantification of renal function markers (blood urea nitrogen (BUN), creatinine, and creatine kinase).

Result

A significant increase in the renal function markers (BUN, 240%; creatinine, 187%; and creatine kinase, 117%), oxidative stress parameters (lipid peroxidation, 192% increase; catalase, 30.5% decrease), cytokines (IL-4, 120%; TNF-α, 129%; and IFN-γ, 133%), and DNA damage was observed in the TAA-treated group. All changes were significantly reversed in the group treated with RSV and TAA (P < 0.05) in combination, with no significant difference compared to the control group.

Conclusion

We conclude that resveratrol shows protection against TAA toxicity in rat kidney with respect to DNA damage, oxidative stress, renal function and cytokine release.

Toxicogenomics - What added Value Do These Approaches Provide for Carcinogen Risk Assessment?

It is still a major challenge to protect humans at workplaces and in the environment. To cope with this task, it is a prerequisite to obtain detailed information on the extent of chemical perturbations of biological pathways, in particular, adaptive vs. adverse effects and the dose-response relationships. This knowledge serves as the basis for the classification of non-carcinogens and carcinogens and for further distinguishing carcinogens in genotoxic (DNA damaging) or non-genotoxic compounds. Basing on quantitative dose-response relationships, points of departures can be derived for chemical risk assessment. In recent years, new methods have shown their capability to support the established rodent models of carcinogenicity testing. In vitro high throughput screening assays assess more comprehensively cell response. In addition, omics technologies were applied to study the mode of action of chemicals whereby the term "toxicogenomics" comprises various technologies such as transcriptomics, epigenomics, or metabolomics. This review aims to summarize the current state of toxicogenomic approaches in risk science and to compare them with established ones. For example, measurement of global transcriptional changes generates meaningful information for toxicological risk assessment such as accurate classification of genotoxic/non-genotoxic carcinogens. Alteration in mRNA expression offers previously unknown insights in the mode of action and enables the definition of key events. Based on these, benchmark doses can be calculated for the transition from an adaptive to an adverse state. In short, this review assesses the potential and challenges of transcriptomics and addresses the impact of other omics technologies on risk assessment in terms of hazard identification and dose-response assessment.

Fibrosis-associated hepatocarcinogenesis revisited: Establishing standard medium-term chemically-induced male and female models

Hepatocellular carcinoma causes ~10% of all cancer-related deaths worldwide, usually emerging in a background of liver fibrosis/cirrhosis (70%-90% of cases). Chemically-induced mouse models for fibrosis-associated hepatocarcinogenesis are widely-applied, resembling the corresponding human disease. Nonetheless, a long time is necessary for the development of preneoplastic/neoplastic lesions. Thus, we proposed an early fibrosis-associated hepatocarcinogenesis model for male and female mice separately, focusing on reducing the experimental time for preneoplastic/neoplastic lesions development and establishing standard models for both sexes. Then, two-week old susceptible C3H/HeJ male and female mice (n = 8 animals/sex/group) received a single dose of diethylnitrosamine (DEN, 10 or 50 mg/Kg). During 2 months, mice received 3 weekly doses of carbon tetrachloride (CCl4, 10% corn oil solution, 0.25 to 1.50 μL/g b.wt.) and they were euthanized at week 17. DEN/CCl4 protocols for males and females displayed clear liver fibrosis, featuring collagen accumulation and hepatic stellate cell activation (α-SMA). In addition, liver from males displayed increased CD68+ macrophage number, COX-2 protein expression and IL-6 levels. The DEN/CCl4 models in both sexes impaired antioxidant defense as well as enhanced hepatocyte proliferation and apoptosis. Moreover, DEN/CCl4-treated male and female developed multiple preneoplastic altered hepatocyte foci and hepatocellular adenomas. As expected, the models showed clear male bias. Therefore, we established standard and suitable fibrosis-associated hepatocarcinogenesis models for male and female mice, shortening the experimental time for the development of hepatocellular preneoplastic/neoplastic lesions in comparison to other classical models.

Animal models for hepatocellular carcinoma

Hepatocellular carcinoma (HCC) represents ~90% of all cases of primary liver cancer and occurs predominantly in patients with underlying chronic liver disease and cirrhosis. Establishing appropriate animal models for HCC is required for basic and translational studies, especially the models that can recapitulate one of the human disease settings. Current animal models can be categorized as chemically-induced, genetically-engineered, xenograft, or a combination of these with each other or with a metabolic insult. A single approach to resemble human HCC in animals is not sufficient. Combining pathogenic insults in animal models may more realistically recapitulate the multiple etiologic agents occurring in humans. Combining chemical injury with metabolic disorder or alcohol consumption in mice reduces the time taken to hepatocarcinogenesis. Genetically-engineering weak activation of HCC-promoting pathways combined with disease-specific injury models will possibly mimic the pathophysiology of human HCC in distinct clinical settings.

Animal models of cholangiocarcinoma

Cholangiocarcinoma (CCA) is an aggressive biliary tract malignancy with a poor overall prognosis. There is a critical need to develop effective targeted therapies for the treatment of this lethal disease. In an effort to address this challenge, preclinical in vivo studies have become paramount in understanding CCA carcinogenesis, progression, and therapy. Various CCA animal models exist including carcinogen-based models in which animals develop CCA after exposure to a carcinogen, genetically engineered mouse models in which genetic changes are induced in mice leading to CCA, murine syngeneic orthotopic models, as well as xenograft tumors derived from xenotransplantation of CCA cells, organoids, and patient-derived tissue. Each type has distinct advantages as well as shortcomings. In the ideal animal model of CCA, the tumor arises from the biliary tract in an immunocompetent host with a species-matched tumor microenvironment. Such a model would also be time-efficient, recapitulate the genetic and histopathological features of human CCA, and predict therapeutic response in humans. Recently developed biliary tract transduction and orthotopic syngeneic transplant mouse models encompass several of these elements. Herein, we review the different animal models of CCA, their advantages and deficiencies, as well as features which mimic human CCA.