The mycotoxin ochratoxin A inhibits DNA topoisomerase II and induces polyploidy in cultured CHO cells

Analytical and Omics-Based Advances in the Study of Drug-Induced Liver Injury

Drug-induced liver injury (DILI) is a significant clinical issue, affecting 1-1.5 million patients annually, and remains a major challenge during drug development-toxicity and safety concerns are the second-highest reason for drug candidate failure. The future prevalence of DILI can be minimized by developing a greater understanding of the biological mechanisms behind DILI. Both qualitative and quantitative analytical techniques are vital to characterizing and investigating DILI. In vitro assays are capable of characterizing specific aspects of a drug's hepatotoxic nature and multiplexed assays are capable of characterizing and scoring a drug's association with DILI. However, an even deeper insight into the perturbations to biological pathways involved in the mechanisms of DILI can be gained through the use of omics-based analytical techniques: genomics, transcriptomics, proteomics, and metabolomics. These omics analytical techniques can offer qualitative and quantitative insight into genetic susceptibilities to DILI, the impact of drug treatment on gene expression, and the effect on protein and metabolite abundance. This review will discuss the analytical techniques that can be applied to characterize and investigate the biological mechanisms of DILI and potential predictive biomarkers.

PRL3 induces polypoid giant cancer cells eliminated by PRL3-zumab to reduce tumor relapse

PRL3, a unique oncotarget, is specifically overexpressed in 80.6% of cancers. In 2003, we reported that PRL3 promotes cell migration, invasion, and metastasis. Herein, firstly, we show that PRL3 induces Polyploid Giant Cancer Cells (PGCCs) formation. PGCCs constitute stem cell-like pools to facilitate cell survival, chemo-resistance, and tumor relapse. The correlations between PRL3 overexpression and PGCCs attributes raised possibilities that PRL3 could be involved in PGCCs formation. Secondly, we show that PRL3⁺ PGCCs co-express the embryonic stem cell markers SOX2 and OCT4 and arise mainly due to incomplete cytokinesis despite extensive DNA damage. Thirdly, we reveal that PRL3⁺ PGCCs tolerate prolonged chemotherapy-induced genotoxic stress via suppression of the pro-apoptotic ATM DNA damage-signaling pathway. Fourthly, we demonstrated PRL3-zumab, a First-in-Class humanized antibody drug against PRL3 oncotarget, could reduce tumor relapse in 'tumor removal' animal model. Finally, we confirmed that PGCCs were enriched in relapse tumors versus primary tumors. PRL3-zumab has been approved for Phase 2 clinical trials in Singapore, US, and China to block all solid tumors. This study further showed PRL3-zumab could potentially serve an 'Adjuvant Immunotherapy' after tumor removal surgery to eliminate PRL3⁺ PGCC stem-like cells, preventing metastasis and relapse.

Risk assessment of ochratoxin A in food

The European Commission asked EFSA to update their 2006 opinion on ochratoxin A (OTA) in food. OTA is produced by fungi of the genus Aspergillus and Penicillium and found as a contaminant in various foods. OTA causes kidney toxicity in different animal species and kidney tumours in rodents. OTA is genotoxic both in vitro and in vivo; however, the mechanisms of genotoxicity are unclear. Direct and indirect genotoxic and non-genotoxic modes of action might each contribute to tumour formation. Since recent studies have raised uncertainty regarding the mode of action for kidney carcinogenicity, it is inappropriate to establish a health-based guidance value (HBGV) and a margin of exposure (MOE) approach was applied. For the characterisation of non-neoplastic effects, a BMDL 10 of 4.73 μg/kg body weight (bw) per day was calculated from kidney lesions observed in pigs. For characterisation of neoplastic effects, a BMDL 10 of 14.5 μg/kg bw per day was calculated from kidney tumours seen in rats. The estimation of chronic dietary exposure resulted in mean and 95th percentile levels ranging from 0.6 to 17.8 and from 2.4 to 51.7 ng/kg bw per day, respectively. Median OTA exposures in breastfed infants ranged from 1.7 to 2.6 ng/kg bw per day, 95th percentile exposures from 5.6 to 8.5 ng/kg bw per day in average/high breast milk consuming infants, respectively. Comparison of exposures with the BMDL 10 based on the non-neoplastic endpoint resulted in MOEs of more than 200 in most consumer groups, indicating a low health concern with the exception of MOEs for high consumers in the younger age groups, indicating a possible health concern. When compared with the BMDL 10 based on the neoplastic endpoint, MOEs were lower than 10,000 for almost all exposure scenarios, including breastfed infants. This would indicate a possible health concern if genotoxicity is direct. Uncertainty in this assessment is high and risk may be overestimated.

Differential impacts of individual and combined exposures of deoxynivalenol and zearalenone on the HepaRG human hepatic cell proteome

Numerous surveys have highlighted the natural co-occurrence of deoxynivalenol (DON) and zearalenone (ZEA) mycotoxins in food and feed. Nevertheless, data regarding cellular mechanisms involved in response to their individual and simultaneous exposures are lacking. In this study, in order to analyze how low mycotoxin doses could impact cellular physiology and homeostasis, proteomic profiles of proliferating human hepatic cells (HepaRG) exposed for 1h and 24h to low DON and ZEA cytotoxicity levels (0.2 and 20μM respectively), alone or in combination, were analyzed by LC-MS/MS. Proteome analyses of mycotoxin-treated cells identified 4000 proteins with about 1.4% and 3.7% of these proteins exhibiting a significantly modified abundance compared to controls after 1h or 24h, respectively. Analysis of the Gene Ontology biological process annotations showed that cell cycle, proliferation and/or development as well as on DNA metabolic processes were affected for most treatments. Overall, different proteins, and thus biological processes, were impacted depending on the considered mycotoxin and exposure duration. Finally, despite the important proteome changes observed following 24h exposure to both mycotoxins, only the uptake of ZEA by the cells was suggested by the mycotoxin quantification in cell supernatants.

BIOLOGICAL SIGNIFICANCE

This study investigated the proteomic changes that occurred after DON and ZEA (individually and in combination) short exposures at low cytotoxicity levels in proliferating HepaRG cells using LC-MS/MS. The obtained results showed that the cellular response is time- and mycotoxin or mixture-dependent. In particular, after 1h exposure, the DON+ZEA combination led to more proteomic changes than DON or ZEA alone, whereas the opposite was observed after 24h. In addition, the significant cellular response to stress induced by ZEA after 24h exposure seemed to be reduced when combined with DON. Thus, these results supported a possible mitigation by the hepatocytes when exposed to the mycotoxin mixture for a long duration. These findings represent an essential step to further explore adaptive cell response to mycotoxin exposure using with more complex incubation kinetics and combining different "omics" tools. Moreover, as mycotoxin quantification in cell supernatants showed different behaviors for DON and ZEA, this also raises the question about how mycotoxins actually trigger the cell response.

Linking site-specific loss of histone acetylation to repression of gene expression by the mycotoxin ochratoxin A

Ochratoxin A (OTA) is a potent renal carcinogen but its mechanism has not been fully resolved. In vitro and in vivo gene expression studies consistently revealed down-regulation of gene expression as the predominant transcriptional response to OTA. Based on the importance of specific histone acetylation marks in regulating gene transcription and our recent finding that OTA inhibits histone acetyltransferases (HATs), leading to loss of acetylation of histones and non-histone proteins, we hypothesized that OTA-mediated repression of gene expression may be causally linked to HAT inhibition and loss of histone acetylation. In this study, we used a novel mass spectrometry approach employing chemical ¹³C-acetylation of unmodified lysine residues for quantification of post-translational acetylation sites to identify site-specific alterations in histone acetylation in human kidney epithelial cells (HK-2) exposed to OTA. These results showed OTA-mediated hypoacetylation at almost all lysine residues of core histones, including loss of acetylation at H3K9 and H3K14, which are hallmarks of gene activation. ChIP-qPCR used to establish a possible link between H3K9 or H3K14 hypoacetylation and OTA-mediated down-regulation of selected genes (AMIGO2, CLASP2, CTNND1) confirmed OTA-mediated H3K9 hypoacetylation at promoter regions of these genes. Integrated analysis of OTA-mediated genome-wide changes in H3K9 acetylation identified by ChIP-Seq with published gene expression data further demonstrated that among OTA-responsive genes almost 80% of hypoacetylated genes were down-regulated, thus confirming an association between H3K9 acetylation status and gene expression of these genes. However, only 7% of OTA repressed genes showed loss of H3K9 acetylation within promoter regions. Interestingly, however, GO analysis and functional enrichment of down-regulated genes showing loss of H3K9 acetylation at their respective promoter regions revealed enrichment of genes involved in the regulation of transcription, including a number of transcription factors that are predicted to directly or indirectly regulate the expression of 98% of OTA repressed genes. Thus, it is possible that histone acetylation changes in a fairly small set of genes but with key function in transcriptional regulation may trigger a cascade of events that may lead to overall repression of gene expression. Taken together, our data provide evidence for a mechanistic link between loss of H3K9 acetylation as a consequence of OTA-mediated inhibition of HATs and repression of gene expression by OTA, thereby affecting cellular processes critical to tumorigenesis.

The effects of the mycotoxin austdiol on cell cycle progression, cytotoxicity and genotoxicity in Chinese hamster ovary (CHO-K1) cells

Austdiol is a mycotoxin mainly produced by Aspergillus ustus and Mycoleptodiscus indicus. These fungi are found in rye, oats, barley, corn and feed grains; thus, as a potential contaminant of human food and animal feed, this mycotoxin is of great concern. As such, the elucidation of the cytotoxicity and mutagenicity of austdiol is important. In this study, austdiol was purified from a rice-oat solid medium culture of M. indicus using chromatographic separation techniques. Chinese hamster ovary (CHO-K1) cells were then used to study the effect of austdiol on mammalian cell cycle, clonogenicity and DNA damage. Austdiol induced cell cycle arrest in G2/M phase, with a decreased S phase population and increased sub-G1 population. Austdiol also increased the polyploid population. These events resulted in cell death detected 7 days after treatment by clonogenic assay. DNA damage represents the main mechanism of action of austdiol, which induces DNA breaks and increases the frequency of micronuclei and nucleoplasmic bridges in binucleated cells in a CHO-K1 cell line. Moreover, cells exposed to austdiol and doxorubicin (DXR) combined treatments presented a reduced number of colonies and increased frequencies of micronuclei and nucleoplasmic bridges compared with negative control and cells treated with austdiol or DXR alone.

Downregulation of Rad51 participates in OTA-induced DNA double-strand breaks in GES-1 cells in vitro

Ochratoxin A (OTA), a mycotoxin produced by ubiquitous Aspergilli, is carcinogenic, teratogenic, and nephrotoxic in both humans and animals. Our previous study found that OTA induced DNA double-strand breaks (DSBs) and resulted in G2 phase arrest in human gastric epithelium immortalized (GES-1) cells. DSBs can cause genomic instability, mutations, and neoplastic transformations, and improper repair of DSBs may lead to the development of cancer. Rad51 is a key protein in the homologous recombination (HR) pathway of DSBs repair. The roles of Rad51 in the repair of DNA damage vary in response to different types of cytotoxic agents. The effect of OTA on Rad51 expression and its putative role in the OTA-induced DSBs in GES-1 cells are still not clear enough. The aim of the current study is to elucidate the role of Rad51 in OTA-induced DSBs in GES-1 cells. The results showed that OTA treatment decreased Rad51 expression in a dose- and time-dependent manner. Specific downregulation of Rad51 by siRNA induced DSBs and G2 phase arrest. Rad51 overexpression by transfection with a Rad51-expressing plasmid partly rescued the DSBs and G2 phase arrest in OTA-treated cells. The findings indicate that downregulation of Rad51 contributes to OTA-induced DNA damage in GES-1 cells. Knockdown of p53 with siRNA for 48h effectively reversed the downregulation of Rad51, and decreased the OTA-induced DSBs in GES-1 cells. In addition, the downregulation of Rad51 induced by OTA could be significantly attenuated with specific ERK inhibitor PD98059 or specific p38 MAPK inhibitor SB203580 pre-treatment in GES-1 cells. Thus, the results suggest that downregulation of Rad51 participates in OTA-induced DNA double-strand breaks in GES-1 cells in vitro. And p53, ERK and p38 signaling pathways are all involved in the process.

Molecular mechanisms underlying ochratoxin A-induced genotoxicity: global gene expression analysis suggests induction of DNA double-strand breaks and cell cycle progression

Ochratoxin A (OTA) is a renal carcinogen primarily affecting the S3 segment of proximal tubules in rodents. In our previous study, we reported that OTA induces reporter gene mutations, primarily deletion mutations, in the renal outer medulla (OM), specifically in the S3 segment. In the present study, to identify genes involved in OTA-induced genotoxicity, we conducted a comparative analysis of global gene expression in the renal cortex (COR) and OM of kidneys from gpt delta rats administered OTA at a carcinogenic dose for 4 weeks. Genes associated with DNA damage and DNA damage repair, and cell cycle regulation were site-specifically changed in the OM. Interestingly, genes that were deregulated in the OM possessed molecular functions such as DNA double-strand break (DSB) repair (Rad18, Brip1, and Brcc3), cell cycle progression (Cyce1, Ccna2, and Ccnb1), G(2)/M arrest in response to DNA damage (Chek1 and Wee1), and p53-associated factors (Phlda3 and Ccng1). Significant increases in the mRNA levels of many of these genes were observed in the OM using real-time RT-PCR. However, genes related to oxidative stress exhibited no differences in either the number or function of altered genes in both the OM and COR. These results suggested that OTA induced DSB and cell cycle progression at the target site. These events other than oxidative stress could trigger genotoxicity leading to OTA-induced renal tumorigenicity.

Ochratoxin A induces oxidative DNA damage and G1 phase arrest in human peripheral blood mononuclear cells in vitro

Ochratoxin A is one of the most abundant food-contaminating mycotoxins worldwide, and its immunosuppressive effects in human caused more and more concern in biomedical field. In the present study, the toxicity of OTA on human peripheral blood mononuclear cells (hPBMC) was explored by analyzing the involvement of oxidative pathway. It was found that OTA treatment led to the release of reactive oxygen species (ROS) and the increase of 8-hydroxydeoxyguanosine (8-OHdG), an important biomarker of oxidative DNA stress. Moreover, we found that OTA treatment induced DNA strand breaks in hPBMC as evidenced by DNA comet tails formation and increased γ-H2AX expression. In addition, OTA could induce cell cycle arrest at G1 phase by down-regulating the expression of CDK4 and cyclinD1 protein, as well as apoptosis in hPBMC in vitro. Pre-treatment of hPBMC with antioxidant, N-acetyl-L-cysteine (NAC), could reduce OTA-induced ROS release and DNA damage, thus confirming the involvement of oxidative DNA damage in the OTA genotoxicity in hPBMC. NAC pre-treatment could also significantly prevent OTA-induced down-regulation of CDK4 and cyclinD1 expression in hPBMC. All the results demonstrated the involvement of oxidative pathway in OTA mediated cytotoxicity in human immune cells, which including the ROS accumulation-oxidative DNA damage-G1 arrest and apoptosis. Our results provide new insights into the molecular mechanisms by which OTA might promote immunotoxicity.

Ochratoxin a and mitotic disruption: mode of action analysis of renal tumor formation by ochratoxin A

The mycotoxin and food contaminant ochratoxin A (OTA) is a potent renal carcinogen in rodents, but its mode of action (MoA) is still poorly defined. In 2006, the European Food Safety Authority concluded that there is a "lack of evidence for the existence of OTA-DNA adducts" and thus insufficient evidence to establish DNA reactivity as a MoA for tumor formation by OTA. In reviewing the available database on OTA toxicity, a MoA for renal carcinogenicity of OTA is developed that involves a combination of genetic instability and increased proliferative drive as consequences of OTA-mediated disruption of mitosis, whereby the organ- and site-specificity of tumor formation by OTA is determined by selective renal uptake of OTA into the proximal tubule epithelium. The proposed MoA is critically assessed with respect to concordance of dose-response of the suggested key events and tumor formation, their temporal association, consistency, and biological plausibility. Uncertainties, data gaps and needs for further research are highlighted.

Mycotoxins in grapes and wine in Europe: occurrence, factors affecting the occurrence and related toxicological effects

In 2006, the European Commission has established maximum levels for ochratoxin A in wine and grape products, using occurrence data up to 2001 and toxicity data up to 2006. This paper presents an up-to-date overview of the occurrence of mycotoxins in grapes and wine produced in Europe in the period 1995-2010. In addition, for the most frequently occurring mycotoxins, factors influencing the occurrence, and the toxicological effects are presented. To evaluate possible trends in occurrence, contamination data were grouped into three periods of time, i.e. 1995-1999, 2000-2006 and 2007-2010. Most of the available contamination data on mycotoxins in grapes and wine refer to ochratoxin A, but occurrence data on this toxin from 2006 onwards are very limited. The occurrence of ochratoxin A is higher in the southern European countries than in the northern countries, and higher in red and sweet wines as compared to white wines. Fumonisins occur frequently, but in low concentrations. Data on the natural occurrence of Alternaria toxins are not available. The most important factors that influence ochratoxin A contamination of grapes and wine include: temperature and relative humidity in the month before harvesting the berries, the type of wine (maceration), and the percentage of damaged berries before vinification. Applying good agricultural practices in the vineyard, including minimizing damaged berries and chemical or biological control of the fungi, are the best methods to limit mycotoxin formation in grapes and wine. Ochratoxin A, Alternaria toxins and fumonisins are toxic to animals. These toxins are of concern to human health, but clear evidence on their relationship with human disease is not available yet. Therefore, more research in this area would be desirable.