Upregulation of miR-34a-5p antagonizes AFB1-induced genotoxicity in F344 rat liver

Aflatoxin B1-induced hepatotoxicity through mitochondrial dysfunction, oxidative stress, and inflammation as central pathological mechanisms: A review of experimental evidence

Aflatoxin B1 (AFB1) is a class of mycotoxin known to contaminate agricultural products, animal feed and animal food products, subsequently causing detrimental effects on human and animal health. AFB1 is the most common and potent aflatoxin found in food and contributes significantly to liver injury as well as the development of hepatocellular carcinoma. Although the liver is a primary target organ for AFB1 toxicity and biotransformation, underlying mechanisms implicated in liver injuries induced by these mycotoxins remain to be fully elucidated for therapeutic purposes. This review aims to dissect the complexities of the pathophysiological and molecular mechanisms implicated in hepatotoxicity induced by AFB1, including mitochondrial dysfunction, oxidative stress and hepatic inflammation. Mechanistically, AFB1 disrupt mitochondrial bioenergetics and membrane potential, promotes mitochondrial cholesterol trafficking and induces mitophagy. Moreover, mitochondrial dysfunction may lead to hepatic oxidative stress as a consequence of uncontrolled production of reactive oxygen species and defects in the antioxidant defense system. Retrieved experimental evidence also showed that AFB1 may lead to hepatic inflammation through gut microbiota dysbiosis, the release of DAMPs and cytokines, and immune cell recruitment. Overall, these mechanisms could be utilized as potential targets to extrapolate treatment for liver injury caused by AFB1.

Effect of aflatoxin B1 and sterigmatocystin on DNA repair genes in common carp

The present study aimed to investigate the short-time (24 h) effect of aflatoxin B1 (AFB1) and sterigmatocystin (STC) on the expression of hsp70, p53, gadd45, and ogg1 genes in common carp hepatopancreas. Our results showed that aflatoxin B1 and sterigmatocystin can stimulate the expression of DNA repair genes, mainly by hour 24. This significant finding contributes to our understanding of the short-term effects of these mycotoxins on ogg1 genes in common carp hepatopancreas. One-year-old common carp juveniles were randomly distributed into five groups (Control, AFB1 0.4 mg kg-1 feed, STC1 1 mg kg-1 feed, STC2 2 mg kg-1 feed, and STC3 3 mg kg-1 feed). Hepatopancreas samples were collected three times (8, 16, and 24 h) in each group. No significant ogg1 and p53 expression changes were observed at 8 and 16 h after exposure. All measured genes were upregulated by the 24th hour in aflatoxin and STC3 groups. An increase in hsp70 gene expression was detected in all groups and all sampling. A significant decrease in gadd45aa gene expression was observed in the aflatoxin B1 group at hour 8. At hour 16, there was no significant change, while at hour 24, all treated groups were significantly different from the control. In summary, our results suggest that aflatoxin B1 and sterigmatocystin can stimulate the expression of DNA repair genes, mainly by hour 24. Further investigations are needed to get information about DNA damage parallel to the DNA repair mechanisms.

MicroRNAs: exploring their role in farm animal disease and mycotoxin challenges

MicroRNAs (miRNAs) serve as key regulators in gene expression and play a crucial role in immune responses, holding a significant promise for diagnosing and managing diseases in farm animals. This review article summarizes current research on the role of miRNAs in various farm animal diseases and mycotoxicosis, highlighting their potential as biomarkers and using them for mitigation strategies. Through an extensive literature review, we focused on the impact of miRNAs in the pathogenesis of several farm animal diseases, including viral and bacterial infections and mycotoxicosis. They regulate gene expression by inducing mRNA deadenylation, decay, or translational inhibition, significantly impacting cellular processes and protein synthesis. The research revealed specific miRNAs associated with the diseases; for instance, gga-miR-M4 is crucial in Marek's disease, and gga-miR-375 tumor-suppressing function in Avian Leukosis. In swine disease such as Porcine Respiratory and Reproductive Syndrome (PRRS) and swine influenza, miRNAs like miR-155 and miR-21-3p emerged as key regulatory factors. Additionally, our review highlighted the interaction between miRNAs and mycotoxins, suggesting miRNAs can be used as a biomarker for mycotoxin exposure. For example, alterations in miRNA expression, such as the dysregulation observed in response to Aflatoxin B1 (AFB1) in chickens, may indicate potential mechanisms for toxin-induced changes in lipid metabolism leading to liver damage. Our findings highlight miRNAs potential for early disease detection and intervention in farm animal disease management, potentially reducing significant economic losses in agriculture. With only a fraction of miRNAs functionally characterized in farm animals, this review underlines more focused research on specific miRNAs altered in distinct diseases, using advanced technologies like CRISPR-Cas9 screening, single-cell sequencing, and integrated multi-omics approaches. Identifying specific miRNA targets offers a novel pathway for early disease detection and the development of mitigation strategies against mycotoxin exposure in farm animals.

Genotoxic and cytotoxic effects of aflatoxin on the reproductive system: Focus on cell cycle dynamics and apoptosis in testicular tissue

Aflatoxins (AFs) are inevitable environmental contaminants that are detrimental to human and animal health. AFs interfere with metabolic processes, metabolizing into different hydroxylated derivatives in the liver, as well as mechanistically induce ROS accumulation, S-phase arrest, DNA damage, and cell apoptosis. Chronic consumption of aflatoxin-contaminated foods can adversely affect the male reproductive system, cause testicular damage, prevent testosterone synthesis, decline sperm quality, and cause infertility. Oxidative stress is the fundamental pathogenesis of aflatoxin-induced reproductive toxicity. The overproduction of reactive oxygen substances can cause testicular failure and disturb the process of spermatogenesis. Mitochondria are susceptible to being impaired by oxidative stress, and its damage is associated with infertility. AFs also disturb the process of spermatogenesis by disrupting the regulation of genes related to the progression of the cell cycle such as cyclins and inducing genes related to apoptosis, thereby weakening fertility and negatively affecting the testicular endocrine potential by suppressing androgen synthesis. Additionally, AFs downregulate ERα expression, potentially negatively impacting spermatogenesis by enhancing the apoptotic mechanism. In this review, we provide new insights into the genotoxic and cytotoxic effects of AFB1 on the male reproductive system with a focus on the cell cycle and apoptosis destruction of testicular tissue.

Allium sativum L. var. Voghiera Reduces Aflatoxin B1 Bioaccessibility and Cytotoxicity In Vitro

The present work focuses on the evaluation of AFB1's bioaccessibility and cytotoxicity in vitro using bread (naturally contaminated) enriched or not enriched with fresh Voghiera garlic (2%). Two different experiments were carried out: experiment 1 (E1), with low-AFB1-concentration breads (1.6-1.7 mg/kg); and experiment 2 (E2), with high-AFB1-concentration breads (96.4-102.7 mg/kg). Eight breads were prepared, four for E1 (experiment 1) and another four for E2 (experiment 2), with each experiment having a control group (C), a garlic-enriched group (2%) (G), an AFB1 group (A), and an AFB1 + garlic group (A + G). Simulated digestion was performed on each type of bread, and gastric and intestinal digests were obtained. AFB1 content in flours, baked bread, and gastric and intestinal digests was measured by High-Performance Liquid Chromatography coupled to Fluorescence Detection. The results demonstrate dose-dependent AFB1 bioaccessibility and that the presence of garlic contributed to its reduction in both doses (7-8%). Moreover, garlic's presence in AFB1-contaminated bread increased cell viability (9-18%) in differentiated Caco-2 cells and mitigated the arrest of S and G2/M phases provoked by AFB1 on Jurkat T cells and reduced apoptosis/necrosis, cellular reactive oxygen species (ROS), and mitochondrial ROS by 16%, 71%, and 24% respectively. The inclusion of garlic as a functional ingredient helped relieve the presence and effects of AFB1.

Immunotoxicity and the mechanisms of aflatoxin B1-induced growth retardation in shrimp and alleviating effects of bile acids

Aflatoxin B1 (AFB1) is one of the most toxic mycotoxins prevalent in the environment and food chain, posing severe health risks to humans and animals. Bile acids are natural detergents synthesized from cholesterol and play a key role in the excretion of toxins in vertebrates. Here, pacific white shrimp (Litopenaeus vannamei) served as an animal model to examine the toxicity mechanisms of AFB1 and assess the potential alleviating effects of bile acids against AFB1. Our results revealed that AFB1 exposure significantly inhibited the growth performance and immune response of shrimp, accompanied by AFB1 accumulation and histological damage. Mechanistically, AFB1-induced DNA damage activated DNA repair mechanisms and induced the arrest of cell cycle via the ATR-cyclin B/cdc2 pathway. Additionally, AFB1 directly suppressed the immune response and growth performance of shrimp by inhibiting Toll and IMD pathways and the secretion of digestive enzymes. Notably, dietary bile acids significantly reduced AFB1 accumulation and alleviated AFB1-induced growth retardation and immunotoxicity in shrimp, and CCKAR, ATR, and Relish may be key mediators of the alleviating effects of bile acids. Our study provided new insights into the toxicity mechanisms of AFB1 in invertebrates and highlighted the potential of bile acids to alleviate AFB1 toxicity.

An in silico toxicogenomic approach in constructing the aflatoxin B1-mediated regulatory network of hub genes in hepatocellular carcinoma

Aflatoxin B1 (AFB1) can cause hepatocellular carcinoma (HCC) through a mutagenic mode of action but can also lead to global changes in gene expression; however, the AFB1 network of molecular pathways involved in HCC is not known. Here, we used toxicogenomic data from human liver cells exposed to AFB1 to infer the network of AFB1-responsive molecular pathways involved in HCC. The following computational tools: STRING, MCODE, cytoHubba, iRegulon, kinase enrichment tool KEA3, and DAVID were used to identify protein-protein interaction network, hub genes, transcription factors (TFs), upstream kinases, and biological processes (BPs). Predicted molecular events were validated with an external dataset, whereas the hub genes in HCC were validated using the UALCAN database. The results revealed an association between AFB1 and the hub genes involved in the cell cycle. We identified TFs that regulate the hub genes and linked them with upstream kinases including cyclin-dependent kinases, mitogen-activated protein kinase 1, and AKT. This approach enabled the construction of the AFB1-mediated regulatory network consisting of upstream kinases, TFs, hub genes, and BPs, thus revealing the signaling hierarchy and information flow that may contribute to AFB1-induced HCC. This could be a useful tool in predicting the molecular mechanisms involved in chemical-induced diseases when available toxicogenomic data exist.

Role of epigenetics in mycotoxin toxicity: a review

Mycotoxins can induce cell cycle disorders, cell proliferation, oxidative stress, and apoptosis through pathways such as those associated with MAPK, JAK2/STAT3, and Bcl-w/caspase-3, and cause reproductive toxicity, immunotoxicity, and genotoxicity. Previous studies have explored the toxicity mechanism of mycotoxins from the levels of DNA, RNA, and proteins, and proved that mycotoxins have epigenetic toxicity. To explore the toxic effects and mechanisms of these changes in mycotoxins, this paper summarizes the changes in DNA methylation, non-coding RNA, RNA and histone modification induced by several common mycotoxins (zearalenone, aflatoxin B1, ochratoxin A, deoxynivalenol, T-2 toxin, etc.) based on epigenetic studies. In addition, the roles of mycotoxin-induced epigenetic toxicity in germ cell maturation, embryonic development, and carcinogenesis are highlighted. In summary, this review provides theoretical support for a better understanding of the regulatory mechanism of mycotoxin epigenotoxicity and the diagnosis and treatment of diseases.

Research progress in toxicological effects and mechanism of aflatoxin B1 toxin

Fungal contamination of animal feed can severely affect the health of farm animals, and result in considerable economic losses. Certain filamentous fungi or molds produce toxic secondary metabolites known as mycotoxins, of which aflatoxins (AFTs) are considered the most critical dietary risk factor for both humans and animals. AFTs are ubiquitous in the environment, soil, and food crops, and aflatoxin B₁(AFB₁) has been identified by the World Health Organization (WHO) as one of the most potent natural group 1A carcinogen. We reviewed the literature on the toxic effects of AFB₁ in humans and animals along with its toxicokinetic properties. The damage induced by AFB₁ in cells and tissues is mainly achieved through cell cycle arrest and inhibition of cell proliferation, and the induction of apoptosis, oxidative stress, endoplasmic reticulum (ER) stress and autophagy. In addition, numerous coding genes and non-coding RNAs have been identified that regulate AFB₁ toxicity. This review is a summary of the current research on the complexity of AFB₁ toxicity, and provides insights into the molecular mechanisms as well as the phenotypic characteristics.

Mitochondrial calcium uniporter involved in foodborne mycotoxin-induced hepatotoxicity

Foodborne mycotoxins are toxic metabolites that are produced by fungi. The widespread contamination of food and its by-products by mycotoxins is a global food safety problem that potentially threatens public health and other exposed animals. Most foodborne mycotoxins induce hepatotoxicity. However, only few studies have investigated the regulatory mechanisms of mitochondrial calcium transport monomers in mycotoxin-induced hepatotoxicity. Therefore, according to relevant studies and reports, this review suggests that intracellular Ca(2 +) homeostasis and mitochondrial Ca(2 +) uniporter are involved in the regulation of mycotoxin-induced hepatotoxicity. This review provides some ideas for future research involving mitochondrial Ca(2 +) uniporter in the molecular targets of mycotoxin-induced hepatotoxicity, as well as a reference for the research and development of related drugs and the treatment of related diseases.

MicroRNA regulates the toxicological mechanism of four mycotoxins in vivo and in vitro

Mycotoxins can cause body poisoning and induce carcinogenesis, often with a high mortality rate. Therefore, it is of great significance to seek new targets that indicate mycotoxin activity and to diagnose and intervene in mycotoxin-induced diseases in their early stages. MicroRNAs (miRNAs) are physiological regulators whose dysregulation is closely related to the development of diseases. They are thus important markers for the occurrence and development of diseases. In this review, consideration is given to the toxicological mechanisms associated with four major mycotoxins (ochratoxin A, aflatoxin B1, deoxynivalenol, and zearalenone). The roles that miRNAs play in these mechanisms and the interactions between them and their target genes are explained, and summarize the important role of histone modifications in their toxicity. As a result, the ways that miRNAs are regulated in the pathogenicity signaling pathways are revealed which highlights the roles played by miRNAs in preventing and controlling the harmful effects of the mycotoxins. It is hoped that this review will provide a theoretical basis for the prevention and control of the damage caused by these mycotoxins.

Application of triple co-cultured cell spheroid model for exploring hepatotoxicity and metabolic pathway of AFB1

The toxicity evaluation suffers from the absence of suitable models capable of replicating in the co-cultured cell microenvironment and the function of specific tissues in vitro. Motivated by this urgent need, this study aimed to describe a novel three-dimensional (3D) liver spheroid model. The model consisted of a triple co-culture of HepG2, EA.hy 926, and LX-2. Subsequently, it was used for the toxicity evaluation of aflatoxin B1 (AFB1), and its advantages over the two-dimensional (2D) model and the mono-type cell spheroid model were assessed. This study examined the effects of AFB1 on cell viability, proliferation, mitochondria, oxidative stress, and cell membranes. The results revealed that AFB1 greatly affected 2D cell membranes and oxidative stress levels (0.01 μg/mL; 24 h), and could also significantly affect 2D cell viability, proliferation, and mitochondria levels (1 μg/mL; 24 h). On the contrary, 3D cells were less susceptible to AFB1. Combined with the analysis of gene expression, both metabolic activation (cytochrome P450; CYP450) and detoxification efficiency (drug-metabolizing enzymes) were found to be higher in 3D cells than in 2D cells. Moreover, 3D cells in triple co-culture outperformed mono-type cell spheroids. Therefore, the advanced 3D co-cultured spheroid model constructed in this study allowed us to more realistically simulate the microenvironment in vitro, and was a valuable and precise model to study mycotoxins.

Aflatoxin B1: metabolism, toxicology, and its involvement in oxidative stress and cancer development

Aflatoxins are a class of carcinogenic mycotoxins produced by Aspergillus fungi, which are widely distributed in nature. Aflatoxin B1 (AFB1) is the most toxic of these compounds and its metabolites have a variety of biological activities, including acute toxicity, teratogenicity, mutagenicity and carcinogenicity, which has been well-characterized to lead to the development of hepatocellular carcinoma (HCC) in humans and animals. This review focuses on the metabolism of AFB1, including epoxidation and DNA adduction, as it concerns the initiation of cancer and the underlying mechanisms. In addition to DNA adduction, inflammation and oxidative stress caused by AFB1 can also participate in the occurrence of cancer. Therefore, the main carcinogenic mechanism of AFB1 related ROS is summarized. This review also describes recent reports of AFB1 exposures in occupational settings. It is hoped that people will pay more attention to occupational health, in order to reduce the incidence of cancer caused by occupational exposure.

Contamination of Aflatoxins Induces Severe Hepatotoxicity Through Multiple Mechanisms

Aflatoxins (AFs) are commonly contaminating mycotoxins in foods and medicinal materials. Since they were first discovered to cause “turkey X” disease in the United Kingdom in the early 1960s, the extreme toxicity of AFs in the human liver received serious attention. The liver is the major target organ where AFs are metabolized and converted into extremely toxic forms to engender hepatotoxicity. AFs influence mitochondrial respiratory function and destroy normal mitochondrial structure. AFs initiate damage to mitochondria and subsequent oxidative stress. AFs block cellular survival pathways, such as autophagy that eliminates impaired cellular structures and the antioxidant system that copes with oxidative stress, which may underlie their high toxicities. AFs induce cell death via intrinsic and extrinsic apoptosis pathways and influence the cell cycle and growth via microribonucleic acids (miRNAs). Furthermore, AFs induce the hepatic local inflammatory microenvironment to exacerbate hepatotoxicity via upregulation of NF-κB signaling pathway and inflammasome assembly in the presence of Kupffer cells (liver innate immunocytes). This review addresses the mechanisms of AFs-induced hepatotoxicity from various aspects and provides background knowledge to better understand AFs-related hepatoxic diseases.

Identification of Translational microRNA Biomarker Candidates for Ketoconazole-Induced Liver Injury Using Next-Generation Sequencing

Drug-induced liver injury (DILI) is a leading cause of acute liver failure. Reliable and translational biomarkers are needed for early detection of DILI. microRNAs (miRNAs) have received wide attention as a novel class of potential DILI biomarkers. However, it is unclear how DILI drugs other than acetaminophen may influence miRNA expression or which miRNAs could serve as useful biomarkers in humans. We selected ketoconazole (KCZ), a classic hepatotoxin, to study miRNA biomarkers for DILI as a proof of concept for a workflow that integrated in vivo, in vitro, and bioinformatics analyses. We examined hepatic miRNA expression in KCZ-treated rats at multiple doses and durations using miRNA-sequencing and correlated our results with conventional DILI biomarkers such as liver histology. Significant dysregulation of rno-miR-34a-5p, rno-miR-331-3p, rno-miR-15b-3p, and rno-miR-676 was associated with cytoplasmic vacuolization, a phenotype in rat livers with KCZ-induced injury, which preceded the elevation of serum liver transaminases (ALT and AST). Between rats and humans, miR-34a-5p, miR-331-3p, and miR-15b-3p were evolutionarily conserved with identical sequences, whereas miR-676 showed 73% sequence similarity. Using quantitative PCR, we found that the levels of hsa-miR-34a-5p, hsa-miR-331-3p, and hsa-miR-15b-3p were significantly elevated in the culture media of HepaRG cells treated with 100 µM KCZ (a concentration that induced cytotoxicity). Additionally, we computationally characterized the miRNA candidates for their gene targeting, target functions, and miRNA/target evolutionary conservation. In conclusion, we identified miR-34a-5p, miR-331-3p, and miR-15b-3p as translational biomarker candidates for early detection of KCZ-induced liver injury with a workflow applicable to computational toxicology studies.

Aflatoxin B1 Induces Neurotoxicity through Reactive Oxygen Species Generation, DNA Damage, Apoptosis, and S-Phase Cell Cycle Arrest

Aflatoxin B1 (AFB₁) is a mycotoxin widely distributed in a variety of food commodities and exhibits strong toxicity toward multiple tissues and organs. However, little is known about its neurotoxicity and the associated mechanism. In this study, we observed that brain integrity was markedly damaged in mice after intragastric administration of AFB₁ (300 μg/kg/day for 30 days). The toxicity of AFB₁ on neuronal cells and the underlying mechanisms were then investigated in the neuroblastoma cell line IMR-32. A cell viability assay showed that the IC50 values of AFB₁ on IMR-32 cells were 6.18 μg/mL and 5.87 μg/mL after treatment for 24 h and 48 h, respectively. ROS levels in IMR-32 cells increased significantly in a time- and AFB₁ concentration-dependent manner, which was associated with the upregulation of NOX2, and downregulation of OXR1, SOD1, and SOD2. Substantial DNA damage associated with the downregulation of PARP1, BRCA2, and RAD51 was also observed. Furthermore, AFB₁ significantly induced S-phase arrest, which is associated with the upregulation of CDKN1A, CDKN2C, and CDKN2D. Finally, AFB₁ induced apoptosis involving CASP3 and BAX. Taken together, AFB₁ manifests a wide range of cytotoxicity on neuronal cells including ROS accumulation, DNA damage, S-phase arrest, and apoptosis-all of which are key factors for understanding the neurotoxicology of AFB₁.

Single-cell sequencing reveals novel mechanisms of Aflatoxin B1-induced hepatotoxicity in S phase-arrested L02 cells

Aflatoxin B1 (AFB1) is widely distributed in nature and is confirmed to be the most toxic of all the aflatoxins, whose predominant metabolism site is the liver. As a well-studied and vital mode of epigenetic modifications, aberrant methylation of the promoters in eukaryotic cells may cause the silence of essential genes, affecting their related transcriptional pathways and ultimately leading to the development of disease and cancers. This study investigated the mechanisms of AFB1-induced hepatotoxicity in S phase-arrested L02 cells using single-cell RNA-seq and single-cell reduced representation bisulfite sequencing (RRBS). AFB1 induced apoptosis and cell cycle S phase arrest, reduced mitochondrial membrane potential (ΔΨm), and increased reactive oxygen species (ROS) generation, as well as the DNA methylation level. Hepatotoxicity mechanism patterns induced by AFB1 in S phase-arrested L02 cells were revealed by combining single-cell RNA-seq with single-cell RRBS analysis, in which DNA methylation played a role via regulating the gonadotropin-releasing hormone receptor pathway, the Wnt signaling pathway, and the TGF-beta signaling pathway. Moreover, a novel strategy for precision toxicology exploration was obtained, including the selection of target cells, multi-group non-directional sequencing, and pathway analysis.

Toxicity of mycotoxins in vivo on vertebrate organisms: A review

Mycotoxins are considered to be a major risk factor affecting human and animal health as they are one of the most dangerous contaminants of food and feed. This review aims to compile the research developed up to date on the toxicological effects that mycotoxins can induce on human health, through the examination of a selected number of studies in vivo. AFB1 shows to be currently the most studied mycotoxin in vivo, followed by DON, ZEA and OTA. Scarce data was found for FBs, PAT, CIT, AOH and Fusarium emerging mycotoxins. The majority of them concerned the investigation of immunotoxicity, whereas the rest consisted in the study of genotoxicity, oxidative stress, hepatotoxicity, cytotoxicity, teratogenicity and neurotoxicity. In order to assess the risk, a wide range of different techniques have been employed across the reviewed studies: qPCR, ELISA, IHC, WB, LC-MS/MS, microscopy, enzymatic assays, microarray and RNA-Seq. In the last decade, the attention has been drawn to immunologic and transcriptomic aspects of mycotoxins' action, confirming their toxicity at molecular level. Even though, more in vivo studies are needed to further investigate their mechanism of action on human health.

Circular RNA Expression Profiling and Selection of Key Circular RNAs in the Hypothalamus of Heat-Acclimated Rats

Circular RNAs (circRNAs) have vital roles in great variety of biological processes. However, expression levels and functions of circRNAs related to heat acclimation (HA) are poorly understood. This study is the first time an in-depth circRNA expression profiling were used to investigate circRNA–miRNA interactions in HA rats in order to further comprehend the mechanisms underlying HA. CircRNA expression profile was performed in rats’ hypothalamus of HA and control group with microarray assays and their functions were predicted by using Bioinformatics analysis. Differential circRNAs and their regulated downstream miRNAs and mRNAs were quantitatively validated by means of quantitative polymerase chain reaction in real-time (RT-qPCR). Enzyme-linked immunosorbent assay (ELISA) was then applied to predict the expression of proteins. In total, 53 circRNAs were expressed distinctively between the HA and Control; up- and down-regulation of circRNAs were 28 and 25, respectively, in HA (fold change > 1.5, P < 0.05). Three circRNAs and two miRNAs and three predicted mRNAs were obviously regulated after validated by RT-qPCR in HA rats. Two proteins expression were proportional to their mRNA changes. Further analysis demonstrates that circRNAs closest to HA can be categorized into three signal pathways: including rno_circRNA_014301-vs-rno-miR-3575-vs-Hif-1α, rno_circRNA_014301-vs-rno-miR-3575-vs-Lppr4, and rno_circRNA_010393-vs-rno-miR-20b-3p-vs-Mfap4 in hypoxia response pathways, substance/energy metabolism, and inflammatory response pathways. Our findings implicate that many circRNAs regulate expressions of genes that interact with each other to exert their functions during HA.

Serum miR-182 is a predictive biomarker for dichotomization of risk of hepatocellular carcinoma in rats

Exploration of animal models leads to discoveries that can reveal candidate biomarkers for translation to human populations. Herein, a model of hepatocarcinogenesis and protection was used in which rats treated with aflatoxin (AFB₁ ) daily for 28 days (200 µg/kg BW) developed tumors compared with rats completely protected from tumors by concurrent administration of the chemoprotective agent, 1-[2-cyano-3-,12-dioxooleana-1,9(11)-dien-28-oyl]imidazole (CDDO-Im). Differential expression of miRNAs in tumors (AFB₁ ) and nontumor (AFB₁  + CDDO-Im) bearing livers and their levels in sera over the life-course of the animals was determined. miRNA transcriptome analysis identified 17 miRNAs significantly upregulated at greater than five-fold in the tumors. The ten most dysregulated miRNAs judged by fold-change and biological significance were selected for further study, including liver-specific miR-122-5p. Validation of sequencing results by real-time PCR confirmed the upregulation of the majority of these miRNAs in tumors, including miR-182, as well as miR-224-5p as the most dysregulated of these miRNAs (over 400-fold). The longitudinal analysis of levels of miR-182 in sera demonstrated significant and persistent increases (5.13-fold; 95% CI: 4.59-5.70). The increase in miR-182 was detected months before any clinical symptoms were present in the animals. By the terminal time point of the study, in addition to elevated levels of serum miR-182, serum miR-122-5p was also found to be increased (>1.5-fold) in animals that developed hepatocarcinomas. Thus, using the data from an unbiased discovery approach of the tissue findings, serum miR-182 was found to track across the complex, multistage process of hepatocarcinogenesis opening an opportunity for translation to human populations.

Aflatoxin B1 induces S phase arrest by upregulating the expression of p21 via MYC, PLK1 and PLD1

Aflatoxin B1 (AFB1), a member of the aflatoxin family, is a common contaminant in foods and feeds, and AFB1 exposure is associated with various clinical conditions. Thus far, research on the toxicity of AFB1 has mainly focused on its induction of liver cancer, but little research has been reported on renal toxicity, especially with regards to the underlying molecular mechanisms. In this study, we found that AFB1 treatment significantly induced kidney damage and reduced kidney weight. The human kidney cell line HEK293T was used to further study the molecular mechanism of the toxicity of AFB1 to kidney cells. We found that AFB1 significantly and dose-dependently induced S phase arrest and upregulated p21 mRNA and protein expression. Upstream of p21, three negative regulators, PLK1, MYC, and PLD1, were significantly downregulated under AFB1 treatment. Consistently, p21 was upregulated, and PLK1, MYC and PLD1 were downregulated in mouse kidney after AFB1 treatment. Interestingly, AFB1 also decreased the physical interaction between PLK1 and MYC and weakened the stability of the MYC protein. Importantly, overexpression of PLK1, MYC and PLD1 significantly blocked the upregulation of p21 and attenuated the S phase arrest caused by AFB1. In summary, AFB1 markedly induces kidney damage and strongly induces S phase arrest by upregulating the expression of p21 via PLK1, PLD1 and MYC, which represents a noval mechanism of the renal toxicity of AFB1.

Egg Yolk Immunoglobulin Supplementation Prevents Rat Liver from Aflatoxin B1-Induced Oxidative Damage and Genotoxicity

Egg yolk immunoglobulins (IgY), as nutraceutical supplement for therapeutic or prophylactic intervention, have been extensively studied. The effects of IgY on small molecular toxin-induced toxicity in animals are unclear. In the present study, the protection of highly purified and specific anti-AFB₁ IgY against AFB₁-induced genotoxicity and oxidative damage on the rat liver model were investigated. Our results revealed that AFB₁ induced significant oxidative damage markers, as well as AFB₁-induced protein expression in antioxidant, pro- and antiapoptosis processes in rat liver. These effects could be significantly inhibited by cogavage with anti-AFB₁ IgY in a dose-dependent manner. However, anti-AFB₁ IgY did not significantly induce hepatic CAT and SOD1. To explore mechanisms, metabolite experiments were established to evaluate the influence of anti-AFB₁ IgY on the absorption of AFB₁ in rats. Middle and high doses of anti-AFB₁ IgY reduced hepatic AFB₁-DNA adducts by 43.3% and 52.9%, AFB₁- N⁷-guanine urinary adducts by 19.6% and 34.4%, and AFB₁-albumin adducts by 10.5% and 21.1%, respectively. The feces of high dose anti-AFB₁ IgY cogavaged rats contained approximately 2-fold higher AFB₁ equivalents at 3-6 h after ingestion than AFB₁ group feces, indicating IgY inhibited AFB₁ uptake. These results had provided insight that anti-AFB₁ IgY could prevent animal organs from damage caused by AFB₁ and will be beneficial for the application of detoxification antibody as a supplement in food.

The Protective Role of Selenium in AFB1-Induced Tissue Damage and Cell Cycle Arrest in Chicken's Bursa of Fabricius

Aflatoxin B₁ (AFB₁) is a naturally occurring secondary metabolites of Aspergillus flavus and Aspergillus parasiticus, and is the most toxic form of aflatoxins. Selenium (Se) with antioxidant and detoxification functions is one of the essential trace elements for human beings and animals. This study aims to evaluate the protective effects of Se on AFB₁-induced tissue damage and cell cycle arrest in bursa of Fabricius (BF) of chickens. The results showed that a dietary supplement of 0.4 mg·kg^-1 Se alleviated the histological lesions induced by AFB₁, as demonstrated by decreasing vacuoles and nuclear debris, and relieving oxidative stress. Furthermore, flow cytometry studies showed that a Se supplement protected AFB₁-induced G₂M phase arrest at 7 days and G₀G₁ phase arrest at 14 and 21 days. Moreover, the mRNA expression results of ATM, Chk2, p53, p21, cdc25, PCNA, cyclin D₁, cyclin E₁, cyclin B₃, CDK6, CDK2, and cdc2 indicated that Se supplement could restore these parameters to be close to those in the control group. It is concluded that a dietary supplement of 0.4 mg kg^-1 Se could diminish AFB₁-induced immune toxicity in chicken's BF by alleviating oxidative damage and cell cycle arrest through an ATM-Chk2-cdc25 route and the ATM-Chk2-p21 pathway.

The molecular mechanism of cell cycle arrest in the Bursa of Fabricius in chick exposed to Aflatoxin B 1

Aflatoxin B₁ shows potent hepatotoxic, carcinogenic, genotoxic, immunotoxic potential in humans and many species of animals. The aim of this study was to clarify the underlying mechanism of G₀G₁ phase and G₂M phase arrest of cell cycle in the bursa of Fabricius in broilers exposed to dietary AFB₁. 144 one-day-old healthy Cobb broilers were randomly divided into two groups and fed on control diet and 0.6 mg·Kg⁻¹ AFB₁ diet for 3 weeks. Histological observation showed that AFB₁ induced the increase of nuclear debris and vacuoles in lymphoid follicle of BF. Results of flow cytometry studies showed that bursal cells arrested in G₂M phase at 7 days of age and blocked in G₀G₁ phase at 14 and 21 days of age following exposure to AFB₁. The qRT-PCR analysis indicated that cell cycle arrested in G₂M phase via ATM-Chk2-cdc25-cyclin B/cdc2 pathway, and blocked in G₀G₁ phase through ATM-Chk2-cdc25-cyclin D/CDK6 pathway and ATM-Chk2-p21-cyclin D/CDK6 route. In a word, our results provided new insights that AFB₁ diet induced G₂M and G₀G₁ phase blockage of BF cells in different periods, and different pathways were activated in different arrested cell cycle phase.

Profound changes in miRNA expression during cancer initiation by aflatoxin B1 and their abrogation by the chemopreventive triterpenoid CDDO-Im

Aflatoxin B₁ (AFB₁ ) is a potent human and animal hepatocarcinogen. To investigate the effects of aflatoxin on miRNA expression during the initiation phase of carcinogenesis, next-generation sequencing was used to analyze liver tissues from F344 rats exposed to 200 μg/kg per day AFB₁ for 4 week. A panel of miRNAs was identified that was upregulated with AFB₁ treatment compared to controls: rno-miR-434-3p, rno-miR-411-5p, rno-miR-221-3p, rno-miR-127-3p, rno-miR-205, rno-miR-429, rno-miR-34a-5p, rno-miR-181c-3p, rno-miR-200b-3p, and rno-miR-541-5p. Analysis of rat livers exposed to AFB₁ plus the chemopreventive triterpenoid CDDO-Im revealed a striking abrogation of this upregulation. These changes were validated by real-time PCR. We also explored the temporal variation in expression of the candidate miRNAs during the 4-week dosing period. Most of the candidate miRNAs were upregulated at week 1 and increased for the duration of AFB₁ dosing over the 4-week period. Treatment with CDDO-Im ameliorated these effects at all time points. All candidate miRNAs were detectable in serum from aflatoxin treated animals; however, there was no significant difference in expression for 7 of the 11 miRNAs examined. Exposure to AFB₁ upregulated miR-122-5p (fivefold), 34a-5p (13-fold), and 181c-3p (170-fold) compared with controls. The findings from this study give insight into epigenetic changes induced by aflatoxin taking place during the initial step of carcinogenesis.

Aflatoxin B1-induced epigenetic alterations: An overview

Aflatoxin B1 (AFB1) is widely distributed in nature, especially in a variety of food commodities. It is confirmed to be the most toxic of all the aflatoxins. The toxicity of AFB1 has been well investigated, and it may result in severe health problems including carcinogenesis, mutagenesis, growth retardation, and immune suppression. Epigenetic modifications including DNA methylation, histone modifications and regulation of non-coding RNA play an important role in AFB1-induced disease and carcinogenesis. To better understand the evidence for AFB1-induced epigenetic alterations and the potential mechanisms of the toxicity of AFB1, we conducted a review of published studies of AFB1-induced epigenetic alterations.

Aberrant methylation of RUNX3 is present in Aflatoxin B1-induced transformation of the L02R cell line

Chronic exposure to aflatoxin B₁ (AFB₁) is linked to the development of hepatocellular carcinoma (HCC). To identify differentially methylated genes involved in AFB₁-induced cell transformation, we analyzed DNA methylation patterns in immortal human hepatocyte L02 cells expressing an oncogenic H-Ras allele (L02R cells) and AFB₁-transformed L02R (L02RT-AFB₁) cells by performing genome-wide methylation profiling. We treated L02R cells with 0.3μM AFB₁ weekly and observed a transformed phenotype at the 17th week post-treatment. The transformed cells (L02RT-AFB₁) could grow in an anchorage independent fashion and form tumors in immunodeficient mice. qRT-PCR was performed to examine whether gene methylation led to a reduction in gene expression of methylated candidate genes. As a result, the expression of the following seven genes including JUNB, RUNX3, NAV1, CXCR4, RARRES1, INTS1, and POLL was down-regulated in transformed L02RT-AFB₁ cells. The reduction of gene expression of these genes could be reversed by treatment of 5-azadeoxycytidine. The methylated CpG sites of RUNX3 genes were verified using bisulfite sequencing PCR (BSP) assay. Furthermore, a dynamic change in RUNX3 methylation was observed over the course of AFB₁-induced cell transformation, which was corresponded to the alteration of gene expression and the extent of DNA damage. In vitro study showed that methylation of RUNX3 tended to abate in L02R cells treated with AFB₁ for a short-term period of time. Notably, hypermethylation of RUNX3 appeared in 70% (14/20) of human hepatocellular carcinomas. Moreover, LINE-1 hypomethylation and dynamic changes of DNMTs, TETs and MeCP2 expression were also observed during AFB₁-induced transformation. Taken together, these observations suggest that aberrant methylation of RUNX3 and LINE-1 might be involved in AFB₁-induced carcinogenesis.

Identifying microRNA panels specifically associated with hepatocellular carcinoma and its different etiologies

AIM

Deregulation of microRNAs (miRNAs) expression has been identified in hepatocellular carcinoma (HCC), but few results are consistent. The objective of this study is to investigate "HCC tumor type specific" and "tumor common" miRNA panels.

METHODS

The authors integrate and analyze clinical, etiologic and miRNA profiles data from 9 types of solid tumors in The Cancer Genome Atlas (TCGA) and HCC data from Columbia University Medical Center (CUMC).

RESULTS

Levels of 33 miRNAs were significant different between HCC tumor and paired non-tumor tissues (over 2-fold changes) after Bonferroni correction for multiple comparisons, and most (28 miRNAs) were down-regulated in HCC tumors. Using this panel, the authors well classified HCC tumor tissues with 4 misclassifications among 48 paired tissues. Validating this panel in an additional 302 HCC tumor tissues, the authors almost perfectly distinguished tumor from non-tumor tissues with only two misclassifications (99% of HCC tissues correctly classified). Evaluating miRNA profiles in 32 independent HCC paired tissues from CUMC, the authors observed 40 miRNAs significantly deregulated in HCC with over 2-fold changes; 14 overlapped with those identified in TCGA. Subgroup analyses by HCC etiology found that 4 upregulated and 8 downregulated miRNAs were significantly associated with alcohol-related HCC. There were 7 and 4 miRNAs significantly associated with hepatitis B virus- and hepatitis C virus-related HCC, respectively. Data for the first time revealed that miR-24-1, miR-130a and miR-505 were significantly down-regulated only in HCC tumors; miR-142 and miR-455 were significantly down-regulated in HCC, but up-regulated in 5 other solid tumors; suggesting their HCC "tumor type specific" characteristics. A panel of 8 miRNAs was significant in at least 5 tumor types, including HCC, and was identified as "tumor common" marker.

CONCLUSION

The authors concluded that aberrant miRNA panels have HCC "tumor type specificity" and may be affected by etiologic factors.

Regulatory mechanisms of microRNA expression

MicroRNAs (miRs, miRNAs) are small molecules of 18-22 nucleotides that serve as important regulators of gene expression at the post-transcriptional level. One of the mechanisms through which miRNAs regulate gene expression involves the interaction of their "seed" sequences primarily with 3'-end and more rarely with 5'-end, of mRNA transcribed from target genes. Numerous studies over the past decade have been devoted to quantitative and qualitative assessment of miRNAs expression and have shown remarkable changes in miRNA expression profiles in various diseases. Thus, profiling of miRNA expression can be an important tool for diagnostics and treatment of disease. However, less attention has been paid towards understanding the underlying reasons for changes in miRNA expression, especially in cancer cells. The purpose of this review is to analyze and systematize current data that explains reasons for changes in the expression of miRNAs. The review will cover both transcriptional (changes in gene expression and promoter hypermethylation) and post-transcriptional (changes in miRNA processing) mechanisms of regulation of miRNA expression, as well as effects of endogenous (hormones, cytokines) and exogenous (xenobiotics) compounds on the miRNA expression. The review will summarize the complex multilevel regulation of miRNA expression, in relation to cell type, physiological state of the body and various external factors.

Epigenetic alterations induced by genotoxic occupational and environmental human chemical carcinogens: A systematic literature review

Accumulating evidence suggests that epigenetic alterations play an important role in chemically-induced carcinogenesis. Although the epigenome and genome may be equally important in carcinogenicity, the genotoxicity of chemical agents and exposure-related transcriptomic responses have been more thoroughly studied and characterized. To better understand the evidence for epigenetic alterations of human carcinogens, and the potential association with genotoxic endpoints, we conducted a systematic review of published studies of genotoxic carcinogens that reported epigenetic endpoints. Specifically, we searched for publications reporting epigenetic effects for the 28 agents and occupations included in Monograph Volume 100F of the International Agency for the Research on Cancer (IARC) that were classified as "carcinogenic to humans" (Group 1) with strong evidence of genotoxic mechanisms of carcinogenesis. We identified a total of 158 studies that evaluated epigenetic alterations for 12 of these 28 carcinogenic agents and occupations (1,3-butadiene, 4-aminobiphenyl, aflatoxins, benzene, benzidine, benzo[a]pyrene, coke production, formaldehyde, occupational exposure as a painter, sulfur mustard, and vinyl chloride). Aberrant DNA methylation was most commonly studied, followed by altered expression of non-coding RNAs and histone changes (totaling 85, 59 and 25 studies, respectively). For 3 carcinogens (aflatoxins, benzene and benzo[a]pyrene), 10 or more studies reported epigenetic effects. However, epigenetic studies were sparse for the remaining 9 carcinogens; for 4 agents, only 1 or 2 published reports were identified. While further research is needed to better identify carcinogenesis-associated epigenetic perturbations for many potential carcinogens, published reports on specific epigenetic endpoints can be systematically identified and increasingly incorporated in cancer hazard assessments.