Comparison of Endothelial Cell Proliferation in Normal Liver and Adipose Tissue in B6C3F1 Mice, F344 Rats, and Humans

Comparative analysis of gene expression between mice and humans in acetaminophen-induced liver injury by integrating bioinformatics analysis

OBJECTIVE

Mice are routinely utilized as animal models of drug-induced liver injury (DILI), however, there are significant differences in the pathogenesis between mice and humans. This study aimed to compare gene expression between humans and mice in acetaminophen (APAP)-induced liver injury (AILI), and investigate the similarities and differences in biological processes between the two species.

METHODS

A pair of public datasets (GSE218879 and GSE120652) obtained from GEO were analyzed using "Limma" package in R language, and differentially expressed genes (DEGs) were identified, including co-expressed DEGs (co-DEGs) and specific-expressed DEGS (specific-DEGs). Analysis of Gene Set Enrichment Analysis (GSEA), Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) were performed analyses for specific-DEGs and co-DEGs. The co-DEGs were also used to construct transcription factor (TF)-gene network, gene-miRNA interactions network and protein-protein interaction (PPI) network for analyzing hub genes.

RESULTS

Mouse samples contained 1052 up-regulated genes and 1064 down-regulated genes, while human samples contained 1156 up-regulated genes and 1557 down-regulated genes. After taking the intersection between the DEGs, only 154 co-down-regulated and 89 co-up-regulated DEGs were identified, with a proportion of less than 10%. It was suggested that significant differences in gene expression between mice and humans in drug-induced liver injury. Mouse-specific-DEGs predominantly engaged in processes related to apoptosis and endoplasmic reticulum stress, while human-specific-DEGs were concentrated around catabolic process. Analysis of co-regulated genes reveals showed that they were mainly enriched in biosynthetic and metabolism-related processes. Then a PPI network which contains 189 nodes and 380 edges was constructed from the co-DEGs and two modules were obtained by Mcode. We screened out 10 hub genes by three algorithms of Degree, MCC and MNC, including CYP7A1, LSS, SREBF1, FASN, CD44, SPP1, ITGAV, ANXA5, LGALS3 and PDGFRA. Besides, TFs such as FOXC1, HINFP, NFKB1, miRNAs like mir-744-5p, mir-335-5p, mir-149-3p, mir-218-5p, mir-10a-5p may be the key regulatory factors of hub genes.

CONCLUSIONS

The DEGs of AILI mice models and those of patients were compared, and common biological processes were identified. The signaling pathways and hub genes in co-expression were identified between mice and humans through a series of bioinformatics analyses, which may be more valuable to reveal molecular mechanisms of AILI.

Research on the Species Difference of the Hepatotoxicity of Medicine Based on Transcriptome

In recent years, several drugs have been withdrawn from use by regulatory bodies owing to hepatotoxicity; therefore, studies on drug-induced liver injury (DILI) are being actively pursued. Most studies evaluating DILI use rats or mice as animal models to determine drug toxicity; however, the toxicity of a drug can vary between rats or mice. These inconsistencies in in vivo studies among different animal models affect the extrapolation of experimental results to humans. Thus, it is particularly important to choose the most suitable animal model to determine drug hepatotoxicity owing to the genomic differences between rats and mice resulting from evolution. In this study, genome-wide transcriptome analysis was used to explore hepatotoxicity caused by differences in species. Our findings provide the preclinical basis to further study the mechanisms of drug hepatotoxicity and aid in the selection of animal models to determine drug safety. We used murine models (Sprague-Dawley and Wistar rats, ICR and Kunming mice) in this study and by using transcriptome sequencing with the differentially expressed genes in rat and mouse livers as the entry point, we explored the mechanism of oxidative stress and the difference in gene expression in the lipid-metabolism pathway between rats and mice. The clinically established hepatotoxic drugs, fructus psoraleae and acetaminophen were used to validate our study. Using pathological studies, we confirmed that oxidative stress in mice was more serious than that in rats, and that Kunming mice were more suited for the study of oxidative stress-related DILI. The validity of our findings was further verified based on gene expression. Thus, our study could serve as a valuable reference for the evaluation of potential preclinical hepatotoxicity. Moreover, it could be used in the prediction and early diagnosis of drug-induced liver injury caused by traditional Chinese medicine or synthetic drugs, thereby providing a new avenue for drug-toxicity studies.

Anti-tumoral effects of exercise on hepatocellular carcinoma growth

Regular physical exercise has many beneficial effects, including antitumor properties, and is associated with a reduced risk of developing hepatocellular carcinoma (HCC). Less is known about the impact of exercise on HCC growth and progression. Here, we investigated the effects of exercise on HCC progression and assessed whether any beneficial effects would be evident under sorafenib treatment and could be mimicked by metformin. American Cancer Institute rats with orthotopic syngeneic HCC derived from Morris Hepatoma‐3924A cells were randomly assigned to exercise (Exe) and sedentary groups, or sorafenib±Exe groups or sorafenib±metformin groups. The Exe groups ran on a motorized treadmill for 60 minutes/day, 5 days/week for 4 weeks. Tumor viable area was decreased by exercise, while cell proliferation and vascular density were reduced. Exercise increased the expression of phosphatase and tensin homolog deleted from chromosome 10 and increased the phosphorylation of adenosine monophosphate‐activated protein kinase, while the phosphorylation of protein kinase B, S6 ribosomal protein, and signal transducer and activator of transcription 3 were decreased. Transcriptomic analysis suggested major effects of exercise were on nontumoral liver rather than tumor tissue. Exercise demonstrated similar effects when combined with sorafenib. Moreover, similar effects were observed in the group treated with sorafenib+metformin, revealing an exercise‐mimicking effect of metformin. Conclusion: Exercise attenuates HCC progression associated with alterations in key signaling pathways, cellular proliferation, tumor vascularization, and necrosis. These beneficial effects are maintained when combined with sorafenib and can be mimicked by metformin. (Hepatology Communications 2018;2:607‐620)

Induction of hemangiosarcoma in mice after chronic treatment with S1P-modulator siponimod and its lack of relevance to rat and human

A high incidence of hemangiosarcoma (HSA) was observed in mice treated for 2 years with siponimod, a sphingosine-1-phosphate receptor 1 (S1P1) functional antagonist, while no such tumors were observed in rats under the same treatment conditions. In 3-month rat (90 mg/kg/day) and 9-month mouse (25 and 75 mg/kg/day) in vivo mechanistic studies, vascular endothelial cell (VEC) activation was observed in both species, but VEC proliferation and persistent increases in circulating placental growth factor 2 (PLGF2) were only seen in the mouse. In mice, these effects were sustained over the 9-month study duration, while in rats increased mitotic gene expression was present at day 3 only and PLGF2 was induced only during the first week of treatment. In the mouse, the persistent VEC activation, mitosis induction, and PLGF2 stimulation likely led to sustained neo-angiogenesis which over life-long treatment may result in HSA formation. In rats, despite sustained VEC activation, the transient mitotic and PLGF2 stimuli did not result in the formation of HSA. In vitro, the mouse and rat primary endothelial cell cultures mirrored their respective in vivo findings for cell proliferation and PLGF2 release. Human VECs, like rat cells, were unresponsive to siponimod treatment with no proliferative response and no release of PLGF2 at all tested concentrations. Hence, it is suggested that the human cells also reproduce a lack of in vivo response to siponimod. In conclusion, the molecular mechanisms leading to siponimod-induced HSA in mice are considered species specific and likely irrelevant to humans.

Effect of polyhexamethylene biguanide on rat liver

Polyhexamethylene biguanide (PHMB), an amphiphilic polymeric biocide, increased liver tumor incidence in male and female rats at 1000 and 1500 mg/L in drinking water, but not at 500 mg/L in previous studies. In another study, PHMB administered in diet at 4000 mg/kg was negative for hepatocellular tumors. The present studies evaluated bioavailability and distribution of PHMB administered in drinking water and diet and possible modes of action (MOA). PHMB in drinking water was unpalatable during the first 3 days, resulting in markedly decreased food consumption and decreased body weight. Ki-67 labeling index was increased in hepatocytes and endothelial cells dose responsively with PHMB administered in drinking water but not diet. Vitamin E had no effect on this. There was no cytotoxicity by histopathology or serum enzymes, and no increase in cytokines TNFα, IL-1α or NF-κB. Focal iron deposition in sinusoidal lining cells was detected. Microarray analyses were non-contributory. No effect on CAR or PPARα activation was detected. ¹⁴C-PHMB administered at 500, 1000, or 1500 mg/L in the drinking water or 4000 mg/kg in the diet was nearly completely absorbed and excreted in urine, with some fecal excretion. The hypothesized MOA for liver tumors induced by PHMB in drinking water is: 1) severe dehydration and starvation because of unpalatability, followed by ingestion with rapid absorption and urinary excretion; 2) increased hepatocyte proliferation; and 3) induction of hepatocellular foci and tumors. The PHMB-induced rat hepatocellular tumors are unlikely to pose a human cancer risk. However, the actual MOA has not been determined.

Mechanistic Modelling of Drug-Induced Liver Injury: Investigating the Role of Innate Immune Responses

Drug-induced liver injury (DILI) remains an adverse event of significant concern for drug development and marketed drugs, and the field would benefit from better tools to identify liver liabilities early in development and/or to mitigate potential DILI risk in otherwise promising drugs. DILIsym software takes a quantitative systems toxicology approach to represent DILI in pre-clinical species and in humans for the mechanistic investigation of liver toxicity. In addition to multiple intrinsic mechanisms of hepatocyte toxicity (ie, oxidative stress, bile acid accumulation, mitochondrial dysfunction), DILIsym includes the interaction between hepatocytes and cells of the innate immune response in the amplification of liver injury and in liver regeneration. The representation of innate immune responses, detailed here, consolidates much of the available data on the innate immune response in DILI within a single framework and affords the opportunity to systematically investigate the contribution of the innate response to DILI.

Scientific and Regulatory Policy Committee (SRPC) Review*

Increased cell proliferation is a central key event in the mode of action for many non-genotoxic carcinogens, and quantitative cell proliferation data play an important role in the cancer risk assessment of many pharmaceutical and environmental compounds. Currently, there is limited unified information on assay standards, reference values, targeted applications, study design issues, and quality control considerations for proliferation data. Here, we review issues in measuring cell proliferation indices, considerations for targeted studies, and applications within current risk assessment frameworks. As the regulatory environment moves toward more prospective evaluations based on quantitative pathway-based models, standardization of proliferation assays will become an increasingly important part of cancer risk assessment. To help address this development, we also discuss the potential role for proliferation data as a component of alternative carcinogenicity testing models. This information should improve consistency of cell proliferation methods and increase efficiency of targeted testing strategies.

Selection of appropriate tumour data sets for Benchmark Dose Modelling (BMD) and derivation of a Margin of Exposure (MoE) for substances that are genotoxic and carcinogenic: considerations of biological relevance of tumour type, data quality and uncertainty assessment

This article addresses a number of concepts related to the selection and modelling of carcinogenicity data for the calculation of a Margin of Exposure. It follows up on the recommendations put forward by the International Life Sciences Institute - European branch in 2010 on the application of the Margin of Exposure (MoE) approach to substances in food that are genotoxic and carcinogenic. The aims are to provide practical guidance on the relevance of animal tumour data for human carcinogenic hazard assessment, appropriate selection of tumour data for Benchmark Dose Modelling, and approaches for dealing with the uncertainty associated with the selection of data for modelling and, consequently, the derived Point of Departure (PoD) used to calculate the MoE. Although the concepts outlined in this article are interrelated, the background expertise needed to address each topic varies. For instance, the expertise needed to make a judgement on biological relevance of a specific tumour type is clearly different to that needed to determine the statistical uncertainty around the data used for modelling a benchmark dose. As such, each topic is dealt with separately to allow those with specialised knowledge to target key areas of guidance and provide a more in-depth discussion on each subject for those new to the concept of the Margin of Exposure approach.

Mode of action associated with development of hemangiosarcoma in mice given pregabalin and assessment of human relevance

Pregabalin increased the incidence of hemangiosarcomas in carcinogenicity studies of 2-year mice but was not tumorigenic in rats. Serum bicarbonate increased within 24 h of pregabalin administration in mice and rats. Rats compensated appropriately, but mice developed metabolic alkalosis and increased blood pH. Local tissue hypoxia and increased endothelial cell proliferation were also confirmed in mice alone. The combination of hypoxia and sustained increases in endothelial cell proliferation, angiogenic growth factors, dysregulated erythropoiesis, and macrophage activation is proposed as the key event in the mode of action (MOA) for hemangiosarcoma formation. Hemangiosarcomas occur spontaneously in untreated control mice but occur only rarely in humans. The International Programme on Chemical Safety and International Life Sciences Institute developed a Human Relevance Framework (HRF) analysis whereby presence or absence of key events can be used to assess human relevance. The HRF combines the MOA with an assessment of biologic plausibility in humans to assess human relevance. This manuscript compares the proposed MOA with Hill criteria, a component of the HRF, for strength, consistency, specificity, temporality, and dose response, with an assessment of key biomarkers in humans, species differences in response to disease conditions, and spontaneous incidence of hemangiosarcoma to evaluate human relevance. Lack of key biomarker events in the MOA in rats, monkeys, and humans supports a species-specific process and demonstrates that the tumor findings in mice are not relevant to humans at the clinical dose of pregabalin. Based on this collective dataset, clinical use of pregabalin would not pose an increased risk for hemangiosarcoma to humans.

Proliferative and nonproliferative lesions of the rat and mouse hepatobiliary system

The INHAND Project (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions in Rats and Mice) is a joint initiative of the Societies of Toxicologic Pathology from Europe (ESTP), Great Britain (BSTP), Japan (JSTP) and North America (STP) to develop an internationally-accepted nomenclature for proliferative and non-proliferative lesions in laboratory animals. The purpose of this publication is to provide a standardized nomenclature and differential diagnosis for classifying microscopic lesions observed in the hepatobiliary system of laboratory rats and mice, with color microphotographs illustrating examples of some lesions. The standardized nomenclature presented in this document is also available for society members electronically on the internet (http://goreni.org). Sources of material included histopathology databases from government, academia, and industrial laboratories throughout the world. Content includes spontaneous and aging lesions as well as lesions induced by exposure to test materials. A widely accepted and utilized international harmonization of nomenclature for lesions of the hepatobiliary system in laboratory animals will decrease confusion among regulatory and scientific research organizations in different countries and provide a common language to increase and enrich international exchanges of information among toxicologists and pathologists.

Hemangiosarcoma in rodents: mode-of-action evaluation and human relevance

Although rarely occurring in humans, hemangiosarcomas (HS) have become important in evaluating the potential human risk of several chemicals, including industrial, agricultural, and pharmaceutical agents. Spontaneous HS arise frequently in mice, less commonly in rats, and frequently in numerous breeds of dogs. This review explores knowledge gaps and uncertainties related to the mode of action (MOA) for the induction of HS in rodents, and evaluates the potential relevance for human risk. For genotoxic chemicals (vinyl chloride and thorotrast), significant information is available concerning the MOA. In contrast, numerous chemicals produce HS in rodents by nongenotoxic, proliferative mechanisms. An overall framework is presented, including direct and indirect actions on endothelial cells, paracrine effects in local tissues, activation of bone marrow endothelial precursor cells, and tissue hypoxia. Numerous obstacles are identified in investigations into the MOA for mouse HS and the relevance of the mouse tumors to humans, including lack of identifiable precursor lesions, usually late occurrence of the tumors, and complexities of endothelial biology. This review proposes a working MOA for HS induced by nongenotoxic compounds that can guide future research in this area. Importantly, a common MOA appears to exist for the nongenotoxic induction of HS, where there appears to be a convergence of multiple initiating events (e.g., hemolysis, decreased respiration, adipocyte growth) leading to either dysregulated angiogenesis and/or erythropoiesis that results from hypoxia and macrophage activation. These later events lead to the release of angiogenic growth factors and cytokines that stimulate endothelial cell proliferation, which, if sustained, provide the milieu that can lead to HS formation.

Effects of the PPARgamma agonist troglitazone on endothelial cells in vivo and in vitro: differences between human and mouse

Peroxisome proliferator-activated receptor gamma (PPARgamma) agonists and PPARgamma/alpha dual agonists have been or are being developed for clinical use in the treatment of type 2 diabetes mellitus and hyperlipidemias. A common tumor finding in rodent carcinogenicity studies for these agonists is hemangioma/hemangiosarcoma in mice but not in rats. We hypothesized that increased endothelial cell proliferation may be involved in the mechanism of PPAR agonist-induced vascular tumors in mice, and we investigated the effects on endothelial cells utilizing troglitazone, the first clinically used PPARgamma agonist, in vivo and in vitro. Troglitazone (400 and 800 mg/kg/day) induced hemangiosarcomas in mice in a 2-year bioassay. We showed that troglitazone increased endothelial cell proliferation in brown and white adipose tissue and liver in mice at sarcomagenic doses after 4 weeks of treatment. Troglitazone was cytotoxic both to human dermal microvascular endothelial cells (HMEC1) and mouse mammary fat pad microvascular endothelial cells (MFP MVEC) at high concentrations. However, MFP MVEC were more resistant to the cytotoxic effects of troglitazone based on the much lower LC(50) in HMEC1 (17.4 muM) compared to MFP MVEC (92.2 muM). Troglitazone increased the proliferation and survival of MFP MVEC but not HMEC1 in growth factor reduced conditions. Our data demonstrate that troglitazone may induce hemangiosarcomas in mice, at least in part, through enhancement of survival and proliferation of microvascular endothelial cells. Such an effect does not occur with human cells, suggesting that human may react differently to exposure to PPAR agonists compared with mice.

Rat Urinary Bladder Carcinogenesis by Dual-Acting PPARalpha + gamma Agonists

Despite clinical promise, dual-acting activators of PPARalpha and gamma (here termed PPARalpha+gamma agonists) have experienced high attrition rates in preclinical and early clinical development, due to toxicity. In some cases, discontinuation was due to carcinogenic effect in the rat urothelium, the epithelial layer lining the urinary bladder, ureters, and kidney pelvis. Chronic pharmacological activation of PPARalpha is invariably associated with cancer in rats and mice. Chronic pharmacological activation of PPARgamma can in some cases also cause cancer in rats and mice. Urothelial cells coexpress PPARalpha as well as PPARgamma, making it plausible that the urothelial carcinogenicity of PPARalpha+gamma agonists may be caused by receptor-mediated effects (exaggerated pharmacology). Based on previously published mode of action data for the PPARalpha+gamma agonist ragaglitazar, and the available literature about the role of PPARalpha and gamma in rodent carcinogenesis, we propose a mode of action hypothesis for the carcinogenic effect of PPARalpha+gamma agonists in the rat urothelium, which combines receptor-mediated and off-target cytotoxic effects. The proposed mode of action hypothesis is being explored in our laboratories, towards understanding the human relevance of the rat cancer findings, and developing rapid in vitro or short-term in vivo screening approaches to faciliate development of new dual-acting PPAR agonist compounds.