Ochratoxin A activates opposing c-MET/PI3K/Akt and MAPK/ERK 1-2 pathways in human proximal tubule HK-2 cells

Membrane Receptor-Mediated Disruption of Cellular Homeostasis: Changes in Intracellular Signaling Pathways Increase the Toxicity of Ochratoxin A

Organisms maintain their cellular homeostatic balance by interacting with their environment through the use of their cell surface receptors. Membrane based receptors such as the transforming growth factor β receptor (TGFR), the prolactin receptor (PRLR), and hepatocyte growth factor receptor (HGFR), along with their associated signaling cascade, play significant roles in retaining cellular homeostasis. While these receptors and related signaling pathways are essential for health of cell and organism, their dysregulation can lead to imbalance in cell function with severe pathological conditions such as cell death or cancer. Ochratoxin A (OTA) can disrupt cellular homeostasis by altering expression levels of these receptors and/or receptor-associated intracellular downstream signaling modulators and/or pattern and levels of their phosphorylation/dephosphorylation. Recent studies have shown that the activity of the TGFR, the PRLR, and HGFR and their associated signaling cascades change upon OTA exposure. A critical evaluation of these findings suggests that while increased activity of the HGFR and TGFR signaling pathways leads to an increase in cell survival and fibrosis, decreased activity of the PRLR signaling pathway leads to tissue damage. This review explores the roles of these receptors in OTA-related pathologies and effects on cellular homeostasis.

Estrogen receptor α mediates alternariol-induced apoptosis and modulation of the invasiveness of ovarian cancer cells

Mycotoxins are secondary metabolites of fungi that may affect both human and animal health. Some of them possess estrogenic activity, due to direct binding to estrogen receptors (ERs) and hence disturb the hormonal balance of the organism. Alternariol (AOH) was previously reported as genotoxic, estrogenic and immunomodulatory agent. However, detailed mechanism of its action has not been fully elucidated. Estrogen receptor α (ERα) was previously reported to modulate the proliferation and invasiveness of ovarian cancer cells. Thus, we decided to verify whether estrogenic-like mycotoxin may affect ovarian cancer cells via ERα. The results showed that AOH induces apoptosis and oxidative stress and that these effects are partially modulated by ERα. Moreover, AOH decreases the invasion and migration of ovarian cancer cells and promotes changes in the expression of genes and proteins that are associated with the invasiveness of cancer i.e. MMP9, SNAIL1/2, ZEB1/2, VIM, CDH1 and CDH2. In conclusion, we postulate that AOH might significantly affect the viability and invasiveness of ovarian cancer cells via modulation of ERα and therefore possibly act as an endocrine disruptive agent in ovarian cancer cells.

Protective Effect of alpha-Tocopherol against Ochratoxin A in Kidney Cell Line HK-2

Food safety is a top priority for the protection of infants and young children. Ochratoxin A (OTA) is an emerging concern due to its high toxicity and occurrence in a wide range of agricultural crops and their derived food products including those foods and snacks destined for infants and young children. OTA is considered as a possible human carcinogen and its main target organ is the kidney. The objective of this study was to investigate the protective effect of α-tocopherol against oxidative stress induced by OTA using human proximal tubule epithelial cells (HK-2). OTA showed dose-dependent increase in cytotoxicity (IC₅₀ = 161 nM, p<0.05) at 48 h, while treatment up to 2 mM α-tocopherol did not change cell viability. Levels of the reduced form of glutathione (GSH) were decreased with α-tocopherol treatment, although the ratio of the oxidative form (GSSG) to GSH remained the same. Among several genes associated with oxidative stress, expression of superoxide dismutase 1 (SOD1), catalase (CAT), glutathione reductase (GSR), and kidney injury molecule-1 (KIM-1) were significantly up-regulated by OTA treatment. CAT and GSR showed decreased expression at 0.5 - 2 mM α-tocopherol and OTA at IC₅₀ value, KIM-1 was decreased at 0.5 mM α-tocopherol and OTA at IC₅₀ value, and nuclear factor erythroid 2-related factor 2 (Nrf2) was decreased at 0.5 - 1 mM α-tocopherol and OTA at IC₅₀ value. In addition, the levels of malondialdehyde (MDA) were increased significantly by OTA while significantly decreased by α-tocopherol. The results show that α-tocopherol may alleviate potential OTA-induced renal damage and oxidative stress through reducing cytotoxicity and enhancing the antioxidant defense systems.

Protective and detoxifying effects conferred by selenium against mycotoxins and livestock viruses: A review

Animal feed can easily be infected with molds during production and storage processes, and this can lead to the production of secondary metabolites, such as mycotoxins, which eventually threaten human and animal health. Furthermore, livestock production is also not free from viral infections. Under these conditions, the essential trace element, selenium (Se), can confer various biological benefits to humans and animals, especially due to its anticancer, antiviral, and antioxidant properties, as well as its ability to regulate immune responses. This article reviews the latest literature on the antagonistic effects of Se on mycotoxin toxicity and viral infections in animals. We outlined the systemic toxicity of mycotoxins and the primary mechanisms of mycotoxin-induced toxicity in this analysis. In addition, we pay close attention to how mycotoxins and viral infections in livestock interact. The use of Se supplementation against mycotoxin-induced toxicity and cattle viral infection was the topic of our final discussion. The coronavirus disease 2019 (COVID-19) pandemic, which is currently causing a health catastrophe, has altered our perspective on health concerns to one that is more holistic and increasingly embraces the One Health Concept, which acknowledges the interdependence of humans, animals, and the environment. In light of this, we have made an effort to present a thorough and wide-ranging background on the protective functions of selenium in successfully reducing mycotoxin toxicity and livestock viral infection. It concluded that mycotoxins could be systemically harmful and pose a severe risk to human and animal health. On the contrary, animal mycotoxins and viral illnesses have a close connection. Last but not least, these findings show that the interaction between Se status and host response to mycotoxins and cattle virus infection is crucial.

Mycotoxins in food and feed: toxicity, preventive challenges, and advanced detection techniques for associated diseases

Mycotoxins are produced primarily as secondary fungal metabolites. Mycotoxins are toxic in nature and naturally produced by various species of fungi, which usually contaminate food and feed ingredients. The growth of these harmful fungi depends on several environmental factors, such as pH, humidity, and temperature; therefore, the mycotoxin distribution also varies among global geographical areas. Various rules and regulations regarding mycotoxins are imposed by the government bodies of each country, which are responsible for addressing global food and health security concerns. Despite this legislation, the incidence of mycotoxin contamination is continuously increasing. In this review, we discuss the geographical regulatory guidelines and recommendations that are implemented around the world to control mycotoxin contamination of food and feed products. Researchers and inventors from various parts of the world have reported several innovations for controlling mycotoxin-associated health consequences. Unfortunately, most of these techniques are restricted to laboratory scales and cannot reach users. Consequently, to date, no single device has been commercialized that can detect all mycotoxins that are naturally available in the environment. Therefore, in this study, we describe severe health hazards that are associated with mycotoxin exposure, their molecular signaling pathways and processes of toxicity, and their genotoxic and cytotoxic effects toward humans and animals. We also discuss recent developments in the construction of a sensitive and specific device that effectively implements mycotoxin identification and detection methods. In addition, our study comprehensively examines the recent advancements in the field for mitigating the health consequences and links them with the molecular and signaling pathways that are activated upon mycotoxin exposure.

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.

Human Proximal Tubule Epithelial Cells (HK-2) as a Sensitive In Vitro System for Ochratoxin A Induced Oxidative Stress

Ochratoxin A (OTA) is a mycotoxin that is potentially carcinogenic to humans. Although its mechanism remains unclear, oxidative stress has been recognized as a plausible cause for the potent renal carcinogenicity observed in experimental animals. The effect of OTA on oxidative stress parameters in two cell lines of LLC-PK1 and HK-2 derived from the kidneys of pig and human, respectively, were investigated and compared. We found that the cytotoxicity of OTA on LLC-PK1 and HK-2 cells was dose- and time-dependent in both cell lines. Furthermore, increased intracellular reactive oxygen species (ROS) induced by OTA in both cell lines were observed in a time-dependent manner. Glutathione (GSH) was depleted by OTA at >48 h in HK-2 but not in LLC-PK1 cells. While the mRNA levels of glucose-6-phosphate dehydrogenase (G6PD) and glutathione peroxidase 1 (GPX1) in LLC-PK1 were down-regulated by 0.67- and 0.66-fold, respectively, those of catalase (CAT), glutathione reductase (GSR), and superoxide dismutase 1 (SOD) in HK-2 were up-regulated by 2.20-, 2.24-, and 2.75-fold, respectively, after 72 h exposure to OTA. Based on these results, we conclude that HK-2 cells are more sensitive to OTA-mediated toxicity than LLC-PK1, and OTA can cause a significant oxidative stress in HK-2 as indicated by changes in the parameter evaluated.

Ochratoxin A-Induced Nephrotoxicity: Up-to-Date Evidence

Ochratoxin A (OTA) is a mycotoxin widely found in various foods and feeds that have a deleterious effect on humans and animals. It has been shown that OTA causes multiorgan toxicity, and the kidney is the main target of OTA among them. This present article aims to review recent and latest intracellular molecular interactions and signaling pathways of OTA-induced nephrotoxicity. Pyroptosis, lipotoxicity, organic anionic membrane transporter, autophagy, the ubiquitin-proteasome system, and histone acetyltransferase have been involved in the renal toxicity caused by OTA. Meanwhile, the literature reviewed the alternative or method against OTA toxicity by reducing ROS production, oxidative stress, activating the Nrf2 pathway, through using nanoparticles, a natural flavonoid, and metal supplement. The present review discloses the molecular mechanism of OTA-induced nephrotoxicity, providing opinions and strategies against OTA toxicity.

Selective Activation of Endoplasmic Reticulum Stress by Reactive-Oxygen-Species-Mediated Ochratoxin A-Induced Apoptosis in Tubular Epithelial Cells

Ochratoxin A (OTA), one of the major food-borne mycotoxins, impacts the health of humans and livestock by contaminating food and feed. However, the underlying mechanism of OTA nephrotoxicity remains unknown. This study demonstrated that OTA induced apoptosis through selective endoplasmic reticulum (ER) stress activation in human renal proximal tubular cells (HK-2). OTA increased ER-stress-related JNK and precursor caspase-4 cleavage apoptotic pathways. Further study revealed that OTA increased reactive oxygen species (ROS) levels, and N-acetyl cysteine (NAC) could reduce OTA-induced JNK-related apoptosis and ROS levels in HK-2 cells. Our results demonstrate that OTA induced ER stress-related apoptosis through an ROS-mediated pathway. This study provides new evidence to clarify the mechanism of OTA-induced nephrotoxicity.

Ochratoxin A induces ERK1/2 phosphorylation-dependent apoptosis through NF-κB/ERK axis in human proximal tubule HK-2 cell line

Ochratoxin A (OTA) is a food contaminant mycotoxin with hazardous effects on human and animal health, primarily affecting the kidneys. OTA's mode of action is not well understood. OTA activates both MAPK/ERK and PI3K/Akt signaling pathways, which play role in apoptosis and cell survival, respectively. OTA is also known to induce toxicity by activating the NF-κB pathway in immune cells. However, its role in determining the cell fate upon OTA exposure in a human kidney cell line (HK-2) has not been fully explored. We made use of pharmacological inhibition of NF-κB to define its role in viability of OTA-treated HK-2 cells. We show that OTA-induced p65 NF-κB subunit translocation into the nucleus in a time-dependent manner using both Western blotting and immunofluorescence (IF). We also document the DNA-binding and reporter gene expression activities of NF-κB by electrophoretic mobility shift (EMSA) and luciferase reporter assays, respectively. Our results indicate that, following 6 h of exposure, OTA fully activates NF-κB pathway and its downstream effectors in HK-2 cells. In addition, Bay11-7085 treatment causes attenuation of the relative levels of OTA-mediated ERK1/2 phosphorylation, suggesting a cross-talk between NF-κB and the MAPK/ERK pathway. Critically, co-treatment of HK-2 cells with OTA and Bay11-7085 leads to the inhibition of OTA-induced apoptosis in a time-dependent manner. Our results support a robust association between NF-κB and the MAPK/ERK pathways in the modulation of apoptotic effects of OTA in HK-2 cells.

Ochratoxin A induces nephrotoxicity in vitro and in vivo via pyroptosis

Ochratoxin A (OTA), a prevalent nephrotoxic mycotoxin contaminant in food and feedstuff, has been reported to induce renal injury. To disclose the nephrotoxicity of continuous administration of OTA and to investigate potential mechanisms related to pyroptosis, male C57BL/6 mice were intraperitoneally injected with 1.0 and 2.0 mg/kg B.W. OTA every other day for 14 days. At 2.0 mg/kg B.W. OTA administration significantly increased histological injury and renal fibrosis molecules (α-SMA, Vimentin, TGF-β) and activated the NOD-like receptor protein 3 (NLRP3) inflammasome and induced pyroptosis compared with control. In the in vitro tests, Madin-Darby canine kidney (MDCK) epithelial cells were exposed to 0-4.0 μg/ml OTA for 24 h in serum-free medium. Data showed that OTA dose-dependently affected cell viability and significantly up-regulated renal fibrosis genes (α-SMA, Vimentin, TGF-β). 2.0 μg/ml OTA significantly induced NLRP3 inflammasome activation and caspase-1-dependent pyroptosis, increasing the expression and secretion of pro-inflammatory cytokines (IL-6, TNF-α) and pyroptosis-related genes (GSDMD, IL-1β, IL-18) in MDCK cells. These outcomes were significantly abrogated after inhibiting NLRP3 activation with inhibitor MCC950 and silencing NLRP3 with small interfering RNA (siRNA). Furthermore, knockdown of caspase-1 also ameliorated OTA-induced renal fibrosis via the inhibition of pyroptosis. Collectively, the chosen doses of OTA-triggered nephrotoxicity through NLRP3 inflammasome activation and caspase-1-dependent pyroptosis both in vitro and in vivo.

Mycotoxin Alternariol (AOH) Affects Viability and Motility of Mammary Breast Epithelial Cells

Mycotoxins are present in everyday diet as common food and feed pollutants. A part of them is still concerned as so-called emerging mycotoxins. Due to the lack of toxicity data, the safety limits and detail molecular mechanism have been not established yet for all of them. Alternariol (AOH), as one of these mycotoxins, produced by Alternaria species, is so far reported as an estrogenic, genotoxic, and immunomodulatory agent; however, its direct effect on human health is not known. Especially, in the case of hormone-dependent tissues which are sensitive to both endogenic, as well as external estrogenic agents, it might be crucial to assess the effect of AOH. Thus, this study evaluated how exposure to AOH affects viability and motility of the human normal mammary gland epithelial in vitro model. We observed that AOH significantly affects viability of cells in a time- and dose-dependent manner. Moreover, the induction of oxidative stress, DNA damage, and cell cycle arrest in the G2/M cell cycle phase was observed. The motility of 184A1 cells was also significantly affected. On the molecular level, AOH induced antioxidative stress response via activation of Nuclear factor erythroid 2-related factor 2 (NRF2) signaling pathway agents, as well as decrease in the phosphorylation of protein kinase B (Akt) and p44/42 (ERK 1-2) molecules, indicating that AOH might affect crucial signaling pathways in both physiological and pathophysiological processes in breast tissue.

Ochratoxin A induces reprogramming of glucose metabolism by switching energy metabolism from oxidative phosphorylation to glycolysis in human gastric epithelium GES-1 cells in vitro

Ochratoxin A (OTA) is a ubiquitous mycotoxin with potential nephrotoxic, hepatotoxic and immunotoxic effects. We previously demonstrated that OTA could cause mitochondrial function disturbance in GES-1 cells in vitro, which lead to the presumption that the glucose metabolism of GES-1 cells will be altered by OTA. Therefore in the present study, we explored the toxicity of OTA on glucose metabolism of GES-1 cells and the molecular mechanism. We found that OTA could induce aerobic glycolysis, evidenced shown by increase of glucose consumption, lactate production and cellular ATP concentration. We further detected expressions of GLUT1 and glycolytic enzymes including HK2, PFK1, PKM2 and LDHA as well as tricarboxylic acid (TCA) cycle-associated enzymes including IDH1, OGDH and CS. The results showed that expression of GLUT1 as well as the activities and expressions of HK2, PFK1 and LDHA were significantly increased while IDH1 and OGDH were reduced by OTA. As to PKM2, western blot showed that OTA could elevated the phospho-PKM2 Ser37 protein level and induce the nuclear accumulation of PKM2, which was further supported by immunofluorescence analyses, in addition, pyruvate kinase activity was reduced by OTA. In conclusion, these findings suggest that OTA exposure induces the metabolic shift from oxidative phosphorylation to aerobic glycolysis via regulating the activities and expressions of glycolysis and TCA-cycle associated molecules in GES-1 cells.

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.

C-MET-dependent signal transduction mediates retinoblastoma growth by regulating PKM2 nuclear translocation

Mesenchymal epithelial transition (C-MET) factor overexpression has been found in many types of cancer and has served as an important molecular target for therapeutic intervention. However, the role of C-MET in retinoblastoma remains largely unclear. The present study aimed to investigate the potential role and mechanism of C-MET in Y79 retinoblastoma cells. We found that C-MET was highly expressed in Y79 retinoblastoma cells, and, in addition, the levels of C-MET were positively correlated with cell proliferation and retinoblastoma growth. Inhibition of C-MET suppressed Y79 retinoblastoma cell proliferation and tumour growth. Mechanistically, we showed that HGF-induced C-MET-dependent signal transduction resulted in ERK 1/2 phosphorylation, which subsequently promoted the nuclear translocation of PKM2. Nuclear PKM2 further interacted with histone H3 and contributed to C-MET-dependent cyclin D1 and c-Myc expression and cell proliferation. These findings highlight the role of C-MET in Y79 retinoblastoma cells and reveal a C-MET-dependent signal transduction mechanism. C-MET may be a potential therapeutic target for retinoblastoma. SIGNIFICANCE OF THE STUDY: We demonstrated a new target of retinoblastoma, C-MET. C-MET-dependent signal transduction promotes Y79 retinoblastoma cell proliferation and tumour growth through ERK 1/2/PKM2/histone H3 signalling pathway. C-MET may be a potential target for retinoblastoma therapy.

Transcriptome Analysis of Ochratoxin A-Induced Apoptosis in Differentiated Caco-2 Cells

Ochratoxin A (OTA), an important mycotoxin that occurs in food and animal feed, has aroused widespread concern in recent years. Previous studies have indicated that OTA causes nephrotoxicity, hepatotoxicity, genotoxicity, immunotoxicity, cytotoxicity, and neurotoxicity. The intestinal toxicity of OTA has gradually become a focus of research, but the mechanisms underlying this toxicity have not been described. Here, differentiated Caco-2 cells were incubated for 48 h with different concentrations of OTA and transcriptome analysis was used to estimate damage to the intestinal barrier. Gene expression profiling was used to compare the characteristics of differentially expressed genes (DEGs). There were altogether 10,090 DEGs, mainly clustered into two downregulation patterns. The Search Tool for Retrieval of Interacting Genes (STRING), which was used to analyze the protein-protein interaction network, indicated that 24 key enzymes were mostly responsible for regulating cell apoptosis. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) analysis was used to validate eight genes, three of which were key genes (CASP3, CDC25B, and EGR1). The results indicated that OTA dose-dependently induces apoptosis in differentiated Caco-2 cells. Transcriptome analysis showed that the impairment of intestinal function caused by OTA might be partly attributed to apoptosis, which is probably associated with downregulation of murine double minute 2 (MDM2) expression and upregulation of Noxa and caspase 3 (CASP3) expression. This study has highlighted the intestinal toxicity of OTA and provided a genome-wide view of biological responses, which provides a theoretical basis for enterotoxicity and should be useful in establishing a maximum residue limit for OTA.

Ochratoxin A Sequentially Activates Autophagy and the Ubiquitin-Proteasome System

Ochratoxin A (OTA) is a carcinogenic mycotoxin, which is produced by Aspergillus and Penicillium genera of fungi and commonly contaminates food and feed. We and others have previously shown that OTA causes sustained activation of PI3K/AKT and MAPK/ERK1-2 signaling pathways in different cell types and animal models. Given the close relationship between cellular signaling activity and protein stability, we were curious whether increased PI3K/AKT and MAPK/ERK1-2 signaling may be the result of OTA-stimulated alterations in proteolytic activity. We show that both of the major proteolytic systems, autophagy, and the ubiquitin-proteasome system (UPS), are activated upon OTA exposure in human kidney proximal tubule HK-2 and mouse embryonic fibroblast (MEF) cells. OTA stimulates transient autophagic activity at early time points of treatment but autophagic activity subsides after 6 h even in the sustained presence of OTA. Interestingly, OTA exposure also results in increased cell death in wild-type MEF cells but not in autophagy-halted Atg5-deficient cells, suggesting that autophagy exerts a pro-death effect on OTA-induced cytotoxicity. In addition, prolonged OTA exposure decreased ubiquitinated protein levels by increasing proteasomal activity. Using purified and cellular proteasomes, we observed enhanced chymotrypsin-, caspase-, and trypsin-like activities of the 26S but not the 20S proteasome in the presence of OTA. However, in the cellular context, increased proteasomal activity depended on prior induction of autophagy. Our results suggest that autophagy and subsequent UPS activation are responsible for sustained activation of PI3K/AKT and MAPK/ERK1-2 pathways through regulating the levels of critical phosphatases VHR/DUSP3, DUSP4, and PHLPP, which are known to be involved in OTA toxicity and carcinogenicity.

MiR-122-5p and miR-326-3p: Potential novel biomarkers for early detection of cadmium exposure

Cadmium is a common environmental and occupational pollutant and can produce toxic effects in a range of organs, especially in kidneys, after long-term exposure. MicroRNAs are ideal candidate biomarkers for various types of disorders, including renal diseases. In this study, we profiled the global miRNA expressions in rat kidneys using miRNA microarrays and found a collection of differentially expressed miRNAs induced by cadmium exposure. Among all of the candidate miRNAs, we identified miR-122-5p and miR-326-3p as early biomarkers for cadmium-induced nephrotoxicity. The two-miRNA signature was validated by quantitative real-time PCR in HK-2 and NRK-52E cells, rat kidney, serum and urine samples, and serum of an occupational population. Our results indicate that miR-122-5p and miR-326-3p may be potential biomarkers for cadmium exposure.

Zinc supplementation alleviates OTA-induced oxidative stress and apoptosis in MDCK cells by up-regulating metallothioneins

AIMS

The present study was to investigate the protective effects of Zn supplementation in OTA-induced apoptosis of Madin-Darby canine kidney (MDCK) epithelial cells and explore the potential mechanisms. Aiming to provides a new insight into the treatment strategy of OTA-induced nephrotoxicity by nutritional regulation.

MAIN METHODS

Initially, through MTT and LDH assay revealed that Zn supplementation significantly suppressed OTA-induced cytotoxicity in MDCK cells. Then, the production of reactive oxygen species (ROS) was detected by using a DCFH-DA assay. Annexin V-FITC/PI, Hoechst 33258 staining and Flow cytometry were used to detect the apoptosis. The expressions of apoptosis-related molecules were determined by RT-PCR, Western blotting. Interestingly, OTA treatment slightly increased the levels of Metallothionein-1 (MT-1) and Metallothionein-2 (MT-2) by using RT-PCR, Western blotting assay; while Zn supplementation further improved the increase of MT-1 and MT-2 induced by OTA. However, the inhibitive effects of Zn supplementation were significantly blocked after double knockdown of MT-1 and MT-2 by using Small Interfering RNA (siRNA) Transfection method.

KEY FINDINGS

Our study provides supportive data for the potential roles of Zn in reducing OTA-induced oxidative stress and apoptosis in MDCK cells.

SIGNIFICANCE

Zn is one of the key structural components of many proteins, which plays an important role in several physiological processes such as cell survival and apoptosis. This metal is expected to contribute to the conservative and adjuvant treatment of kidney disease and should therefore be investigated further.

An in vitro attempt at precision toxicology reveals the involvement of DNA methylation alteration in ochratoxin A-induced G0/G1 phase arrest

Precision toxicology evaluates the toxicity of certain substances by isolating a small group of cells with a typical phenotype of interest followed by a single cell sequencing-based analysis. In this in vitro attempt, ochratoxin A (OTA), a typical mycotoxin and food contaminant, is found to induce G0/G1 phase cell cycle arrest in human renal proximal tubular HKC cells at a concentration of 20 μM after a 24h-treatment. A small number of G0/G1 phase HKC cells are evaluated in both the presence and absence of OTA. These cells are sorted with a flow cytometer and subjected to mRNA and DNA methylation sequencing using Smart-Seq2 and single-cell reduced-representation bisulfite sequencing (scRRBS) technology, respectively. Integrated analysis of the transcriptome and methylome profiles reveals that OTA causes abnormal expression of the essential genes that regulate G1/S phase transition, act as signal transductors in G1 DNA damage checkpoints, and associate with the anaphase-promoting complex/cyclosome. The alteration of their DNA methylation status is a significant underlying epigenetic mechanism. Furthermore, Notch signaling and Ras/MAPK/CREB pathways are found to be suppressed by OTA. This attempt at precision toxicology paves the way for a deeper understanding of OTA toxicity and provides an innovative strategy to researchers in the toxicology and pharmacology field.

Ochratoxin A suppresses proliferation of Sertoli and Leydig cells in mice

Ochratoxin A (OTA) is a mycotoxin originating from Penicillium and Aspergillus. In addition to toxic effects in various tissues and cells, including neurons, immune cells, hepatocytes, and nephrons, it also causes carcinogenesis and teratogenesis. Although the negative effects of OTA with respect to the pathogenesis of diseases and the malfunction of various organs have been studied widely, the biological signaling mechanisms in testicular cells are less well known. Therefore, we determined the hazardous effect of OTA in two types of testicular cells: TM3 (mouse Leydig cells) and TM4 (mouse Sertoli cells). Treatment with OTA led to a significant decrease in the proliferation of both cell lines, as revealed by an increased proportion of cells in the sub-G1 phase. In addition, the phosphorylation of signaling molecules belonging to the PI3K (Akt, P70S6K, and S6) and MAPK (ERK1/2 and JNK) pathways was regulated by OTA in a dose-dependent manner in TM3 and TM4 cells. Furthermore, the combination treatment of OTA and signaling inhibitors (LY294002, U0126, or SP600125) exerted synergistic antiproliferative effects in TM3 and TM4 cells. OTA also reduced the concentration of calcium ions in the cytosol and mitochondria, which disrupted the calcium homeostasis necessary for maintaining the normal physiological functions of testicular cells. In conclusion, the results of the present study demonstrate the mechanism underlying the antiproliferative effects of OTA in mouse testicular cells. Exposure to OTA may result in abnormal sperm maturation and the failure of spermatogenesis, which leads to male infertility.

Effects of ochratoxin A on ER stress, MAPK signaling pathway and autophagy of kidney and spleen in pigs

Ochratoxin A (OTA), a worldwide mycotoxin found in food and feeds, is a potent nephrotoxin and immunotoxin in animals and humans. This research was conducted to evaluate whether endoplasmic reticulum (ER) stress, MAPK signaling pathway and autophagy were induced by OTA in kidney and spleen of pigs. Twenty-seven crossbred pigs randomly allocated to 3 groups were fed for 42 days ad libitum a basal diet without (Con group, 0.00 μg OTA/kg) and with supplementation of OTA at 400 (OTA-L group) and 800 μg/kg (OTA-H group). From each group, 6 pigs were randomly selected for blood collection on days 0, 21, and 42 and 3 pigs were randomly selected for tissue collection on day 42. The results showed that OTA at 400 and 800 μg/kg diets significantly increased OTA concentrations in serum and kidney and spleen induced the histopathological lesions of kidney and spleen, decreased TCR-stimulated T lymphocyte viabilities and IL-2 concentration, increased TNF-α concentration, and decreased T-AOC levels. OTA increased glucose regulated protein 78, p38, and ERK1/2 phosphorylation, and LC3 II and Atg5 protein expression in kidney and spleen of pigs. These results provide new insights into the relationship between OTA and ER stress, p38 and ERK1/2 MAPK signaling pathway and autophagy in pigs.

Ochratoxin A induces nephrotoxicity and immunotoxicity through different MAPK signaling pathways in PK15 cells and porcine primary splenocytes

Ochratoxin A (OTA) is reported to be a potent nephrotoxin and immunotoxin in animals and humans. However, the mechanisms underlying OTA toxicity have not been clearly determined until now. Toxicity of OTA and its mechanism was investigated in PK15 cells and in porcine primary splenocytes. The results showed that OTA at 2.0-8.0 μg/mL for 24 h induced cytotoxicity and apoptosis in a dose-dependent manner in PK 15 cells. OTA at 0.5-4.0 μg/mL for 24 h induced cytotoxicity and apoptosis in a dose-dependent manner in porcine primary splenocytes. In addition, OTA induced p38 and ERK1/2 phosphorylation both in PK15 cells and porcine primary splenocytes. Knock-down of p38 instead of ERK by their specific siRNA significantly eliminated the nephrotoxicity induced by OTA. Contrary, knock-down of ERK1/2 instead of p38 by their specific siRNA significantly eliminated the immunotoxicity induced by OTA. The observed effects indicate that OTA induced nephrotoxicity by p38 signaling pathway in PK15 cells and immunotoxicity by ERK signaling pathway in porcine primary splenocytes.

A Review: Epigenetic Mechanism in Ochratoxin A Toxicity Studies

Ochratoxin A (OTA) is a natural contaminant that has displayed nephrotoxicity and hepatotoxicity in mammals. It contaminates a great variety of foodstuffs and threatens people's lives. The molecular mechanism of OTA-induced toxicity has been studied since 1965. Moreover, epigenetic mechanisms are also studied in OTA-induced toxicity. Additionally, the mode of OTA epigenetic research has been advanced in research hotspots. However, there is still no epigenetic study of OTA-induced toxicity. In this review, we discuss the relationship between these epigenetic mechanisms and OTA-induced toxicity. We found that studies on the epigenetic mechanisms of OTA-induced toxicity all chose the whole kidney or liver as the model, which cannot reveal the real change in DNA methylation or miRNAs or histone in the target sites of OTA. Our recommendations are as follows: (1) the specific target site of OTA should be detected by advanced technologies; and (2) competing endogenous RNAs (ceRNA) should be explored with OTA.

Neutrophil gelatinase-associated lipocalin production negatively correlates with HK-2 cell impairment: Evaluation of NGAL as a marker of toxicity in HK-2 cells

Neutrophil gelatinase-associated lipocalin is an extracellular protein produced mostly in kidney. Recently, it has become a promising biomarker of renal damage in vivo. On the other hand, the validation of NGAL as a biomarker for nephrotoxicity estimation in vitro has not been characterized in detail yet. Since the HK-2 cells are frequently used human kidney cell line, we aimed to characterize the production of NGAL in these cells and to evaluate NGAL as a possible marker of cell impairment. We used heavy metals (mercury, cadmium), peroxide, drugs (acetaminophen, gentamicin) and cisplatin to mimic nephrotoxicity. HK-2 cells were incubated with selected compounds for 1-24h and cell viability was measured together with extracellular NGAL production. We proved that HK-2 cells possess a capacity to produce NGAL in amount of 2pg/ml/h. We found a change in cell viability after 24h incubation with all tested toxic compounds. The largest decrease of the viability was detected in mercury, acetaminophen, cisplatin and gentamicin. Unexpectedly, we found also a significant decrease in NGAL production in HK-2 cells treated with these toxins for 24h: to 11±5%, 54±5%, 57±6% and 76±9% respectively, compared with controls (=100%). Our results were followed with qPCR analysis when we found no significant increase in LCN2 gene expression after 24h incubation. We conclude that extracellular NGAL production negatively correlates with HK-2 cell impairment.

Ochratoxin A: Molecular Interactions, Mechanisms of Toxicity and Prevention at the Molecular Level

Ochratoxin A (OTA) is a widely-spread mycotoxin all over the world causing major health risks. The focus of the present review is on the molecular and cellular interactions of OTA. In order to get better insight into the mechanism of its toxicity and on the several attempts made for prevention or attenuation of its toxic action, a detailed description is given on chemistry and toxicokinetics of this mycotoxin. The mode of action of OTA is not clearly understood yet, and seems to be very complex. Inhibition of protein synthesis and energy production, induction of oxidative stress, DNA adduct formation, as well as apoptosis/necrosis and cell cycle arrest are possibly involved in its toxic action. Since OTA binds very strongly to human and animal albumin, a major emphasis is done regarding OTA-albumin interaction. Displacement of OTA from albumin by drugs and by natural flavonoids are discussed in detail, hypothesizing their potentially beneficial effect in order to prevent or attenuate the OTA-induced toxic consequences.

Pre-clinical risk assessment and therapeutic potential of antitumor lipopeptide ‘Iturin A’ in an in vivo and in vitro model

Microbial lipopeptide “Iturin A” is a versatile bio-active molecule with potent antitumor action. Pre-clinical study of this lipopeptide showed very minimum toxicity in rodent model.

Recent progress in fungus-derived bioactive agents for targeting of signaling machinery in cancer cells

It is becoming increasingly understood that tumor cells may have different mutations and dependencies on diverse intracellular signaling cascades for survival or metastatic potential. Overexpression of oncogenes, inactivation of tumor suppressor genes, genetic/epigenetic mutations, genomic instability, and loss of apoptotic cell death are some of the mechanisms that have been widely investigated in molecular oncology. We partition this multicomponent review into the most recent evidence on the anticancer activity of fungal substances obtained from in vitro and xenografted models, and these fungal substances modulate expression of oncogenic and tumor suppressor miRNAs. There are some outstanding questions regarding fungus-derived chemical-induced modulation of intracellular signaling networks in different cancer cell lines and preclinical models. Certain hints have emerged, emphasizing mechanisms via which apoptosis can be restored in TRAIL-resistant cancer cells. Reconceptualization of the knowledge obtained from these emerging areas of research will enable us to potentially identify natural agents with notable anticancer activity and minimal off-target effects. Integration of experimentally verified evidence obtained from cancer cell line gene expression with large-scale functional screening results and pharmacological sensitivity data will be helpful in identification of therapeutics with substantial efficacy. New tools and technologies will further deepen our understanding of the signaling networks that underlie the development of cancer, metastasis, and resistance to different therapeutics at both a personal and systems-wide level.